BIGGERTurbo?

[DA BIG ONE]

Been researching this on the web w/o any luck.

I have the GM-8 and would like to upgrade to something larger to burn all that extra fuel, and beat back egt's.

Who out there even offers upgrades for our turbo turbines and compressors?

[markrinker]

How about BIGGER FUEL first?

I was told by Bill Heath that his Maxi-Torque 2.0 chip 'approaches the limits of the DS4 injection pump'.

Don't see alot of black smoke, unless I mash the pedal, so I don't think I need more turbo - YET :D

[BigDiesel]

I'm going to use a PDR HX35 Turbo when I get around to intalling my new engine.

http://www.piersdiesel.com/Hx35.htm

[DA BIG ONE]

If I could get more than 14psi out of my GM-8, say 17/18 lbs that may do.

[rjschoolcraft]

Should be able to... I was running 18 psi with my GM-4. However, it is not as efficient at that level as a bigger unit would be.

[grape]

don't ever change turbo's, just run more boost........that's why they make more than 1 inlet wheel and design for turbos. :rolleyes:

[rjschoolcraft]

For those of us less-enlightened individuals, would you care to explain that statement? A turbo charger is made up of three modules: a centrifugal compressor, a support housing and a drive turbine. The compressor and the turbine must be properly matched to work as desired. Yes, components can be mixed and matched, but you still have to wind up with a compressor and turbine that are matched mechanically and aerodynamically. They also make different turbine wheels and turbine housings...

[grape]

it's like talking to a wall in here. I think i'm done talking, you can move more air through the same engine WITH LESS BOOST, with a different compressor wheel. People here still can't comprehend that so I'm done beating a dead horse.

[rjschoolcraft]

That's right, I'm an idiot. Boy, I feel better.

When calculating flow in a system, the control volume concept is used. Consider the intake plenum and draw an imaginary control volume around it. Flow in to the control volume has to equal flow out during steady state conditions, otherwise pressure would increase uncontrollably until something breaks to relieve it.

Consider the mass flow through a compressor impeller and housing running at 10 psi outlet pressure (boost pressure in our engine). Now consider the mass flow through our engine at some rpm with 10 psi manifold pressure (boost pressure). For the pressure in the intake manifold (boost pressure) to remain at the 10 psi level, the mass flow through the impeller and the mass flow through the engine must be equal.

Two things affect the pressure in the plenum (our control volume): mass within the volume and temperature of that mass. The more mass in the volume the higher the pressure. The higher the temperature, the higher the pressure.

Centrifugal compressors move mass through centrifugal force as they spin, flinging the mass outward. The faster the impeller spins, the more mass gets moved and the more pressure gets built up down stream (to a point, where mechanical and aerodynamic limits take over).

Compressors are designed to operate over a particular speed range and pressure ratio range and are rated by the mass flow rate (lbm/sec). When a compressor is operated off design point to move more mass, the outlet temperature increases accordingly, due to the lower efficiency of the compressor at that point. For instance, let's say our impeller has a certain tip diameter and a certain design speed. For these conditions it moves a certain amount of air (mass). Now let's say we want more mass moved. We can increase the speed of the compressor to accomplish this. We could also introduce a new impeller with a larger tip radius and run it at the previously established speed. Other parameters would likely change as well, such as the curvature of the blades and the shape of the inducer. The first approach is less efficient than the second, therefore, more work must be put into the compressor in the first instance than in the second. However, the first instance is much cheaper and easier, since no hardware changes were necessary. The outlet temperature will be higher in the first case, which can affect outlet pressure.

In our control volume, the temperature of the charge can be controlled via charge air cooling so that in either case the actual temperature of the air in the plenum (control volume) is essentially the same. Therefore, boost pressure is purely a function of the mass flow rate...in and out...period.

Grape,

You can quit if you want to, won't hurt my feelings. It'd be best if you didn't. Maybe some of us idiots could learn something. But, you'd have to learn to explain your comments rather than just laying them out as law or inviolate pronouncements.

Hope you choose to stay on board.

Edited for spelling error. 3/5/2005.

[ 03-05-2005, 07:28 AM: Message edited by: ronniejoe ]

[patrick m.]

not everyone, my truck is the perfect example of just that.
more power from a different turbo, but less pressure.

heres an example, i used to have the GM-4, (blah)it would max at about 15 psi (overcome the vac pull against w.g.)

the Borg warner i have now easily makes more power at say....9psi that the factory "4". im comfortable saying the Borg makes more power at 10 psi, than the factory unit at 15 psi.

of course, im still looking for more :D

[rjschoolcraft]

Patrick,

You're talking power... Grape is talking moving air. There's a difference.

If you read what I wrote, you'll see that I said the efficiency is a factor. Your bigger unit is more efficient than the factory unit at the conditions you're operating...therefore, you have more useable power at a lower boost pressure.

[DA BIG ONE]

Ok, Who has a selection of larger compressor wheels and housings for the GM-8?

[gmctd]

I cannot quite understand how putting a larger fan on the input will increase the engine's mechanical displacement = bore x stroke, or flow rate = bore x stroke x unit of time.

It is impossible for this 400cuin engine to pump - displace - more than 400 cubic feet of air per minute at 3000rpm, without increasing rpm.

Do the math, grape.......

Now, I can understand increasing the turbine wheel diameter and\or nozzle area to improve the intake-exhaust differential pressure ratio.

Right now, we got 8psi in, 22psi out - not bad, but not good, because it steadily climbs from there, and I ain't talking linearly.
Exhaust pressure climbs much faster than Boost.

Reduce exhaust back-pressure, increase power from same intake charge (Boost Pressure).

That is the ONLY way to improve flo thruput at same input pressure - still does NOT increase displacement - 400cuin, or rate - 400cuin x rpm x time period.

[Jim P]

Grape, could you please explain this a little further.

I am no expert on turbos so this is just a stab in the dark

If the size of the compressor wheel is increased, then the turbo would not have spin as fast to make the same amount of boost. Since it is spinning slower it would not require as much exhaust pressure to drive the turbo. This decreased exhaust pressure would allow more air to get in the engine and make more power.


Now this part I am pretty sure about but I still open to corrections from anyone that actually knows.

Lets assume an engine has 10 psi of exhaust pressure. The piston moves up in the exhaust stroke forcing the exhaust out the exhaust valve. When the valve closes the cylinder still has 10 psi of pressure inside it. Then the intake valve opens and the boost pressure tries to cram air into the cylinder. The only problem is that this cylinder already has 10 psi to begin with. So the boost has to have more than 10 psi before any air will begin to flow into the cylinder. So anything we do to increase the effeciency of the turbo would allow more of the boosted air to make its way into the cylinder. Lets assume that we do something to increase the turbos effeciency and now the engine only has 5 psi of back pressure. Now , when the intake valve opens, the air will start to flow in at anything above 5 psi instead of 10 psi. So the engine should now run like it has 5 psi more boost eventhough it stayed the same.


I have a gm-8 turbo that the compressor housing is chewed up on. I asked a turbo rebuilder about boring out this housing and installing a bigger wheel and he said it would work and the engine would have more power. I posted this on this forum and some people didn't think it would work so I never did do it. I just may do it though to find out for my self.

[rjschoolcraft]

Jim,

Your comments about a larger compressor impeller are right, but your comment about the turbine not working as hard isn't necessarily. It takes a certain amount of work (read energy) to compress air and move a certain amount of mass. The work the turbine has to do will be more than the amount of work required to compress the air because of efficiency issues. If impeller B is more efficient than impeller A, the turbine will need to do less work. However, if impeller B is so much larger that its speed is much less than the design speed of the turbine, it will take more energy to drive because the turbine is so far off of point.

Your idea about remaking a GM8 should work, as long as you get the shroud profile relatively similar to whatever impeller you use. The turbine will now be working off design point, but there is quite a bit of flexibility.

[Jim P]

Ronniejoe,

I understand what you are saying. I realize that the larger compressor wheel will require just as much enengy to drive it. I was just thinking that maybe the smaller wheel is wasting some of the exhaust wheels' energy. This energy could be used up doing nothing more than producing heat. Since it has to spin so fast to produce the required boost, it is causing much more friction with the air and producing heat instead of boost.

I am not trying to dispute what you are saying, just trying to look at it from a different angle and maybe get Grape to fill in the blanks. He knows something, I personally would be very interested in what he has to say.

I have not done any turbo swapping on a truck but I do have experience helping a guy with his pulling tractor. The rules limit the size of their turbo but one thing he does is experiment with different sized exhaust housings. The smaller housings make real good boost right off the line but act like an exhaust brake at the end of the track. The bigger housings make the turbo lazy at the start but if you can get it spooled up, it makes more power. The idea is to find that happy medium.

[ 01-18-2005, 04:45 PM: Message edited by: Jim P ]

[rjschoolcraft]

You're correct.

If you were overspeeding an impeller to make a particular level of boost, a larger impeller turning slower would take less energy to drive and bring the turbine back into its speed range.

I'd like for grape to explain, too. That's why I asked. He seems to be put off by my ignorance, though. I can't help that.

[patrick m.]

i believe im going to adapt the opinion that there is no perfect turbo....just the NEXT turbo :D


see related post....DA, if you would like to "test drive" a different turbo, i have a couple. I could box one up and send it to you (if you paid the postage)

[RT]

This turbo stuff is all quite confusing. I changed from a GM1 to a GM4 just because the GM1's seals were shot. The GM4 makes more power, spools sooner and seemingly feels stronger with less boost. This doesn't make any sense unless it is simply less restrictive than the GM1 and less "backpressure" between the turbine and exhaust ports means more power? I would like to experiment with other turbos and was looking at a Holset from a Cummins. Problem is I have heard the stock Holset's don't flow enough on the exhaust side, something about a 12cm or 14cm exhaust housing. Since the 6.5 is approx. 10% larger than the 5.9 I figure this will just exacerbate the problem. Granted my truck is pretty stock so I don't know what gains if any I would see from the turbo swap anyway. If I could find a wastegated Holset with a 16cm housing I would like to give it a try just to see though. Too bad more people don't seem to know what really should be done to improve the 6.5's turbo. RT

[dieseldummy]

Bigger = better right? Not always. I'm with Patrick on this one. There is no perfect turbo, just the next experiement... I've tried: GM-3, GM-4, Garrett with 2 exhaust housing sizes, different Garrett with 1 ehxaust size, M&W (RayJay I think), and a Holset. Currently I am satisfied with the Holset although I am looking into compressor upgrades... The GM-3 was stock on my pickup wouldn't make more than 14 lbs of boost and would choke the engine up above 2700 rpms no matter what. GM-4 was better would make 15+ lbs of boost, but would still choke the engine up at higher rpms. Both the GM series would run high egts as well. The first and second Garretts with either exhaust housings was somewhat laggy and wouldn't make more than 10-12 lbs of boost. It did however make more power than the GM series because of less backpressure but still had exsessive egts. The M&W was off of a JD 4020 tractor, 404 cu. 2100 max rpms. It was just something I found in the neighbors shed and was screwing around and tried it. It would make 15 lbs of boost and would pull strong up to redline, once again however high egts. The Holset I currently run is a WH1C (which is basicly a HX-35) will make 24+ lbs off boost, pulls stong up to the rev limiter and keeps cool doing it. What does all this mean? Take it for what it's worth, but to me more boost made efficiently means more power, but I'm no expert, just a tinkerer that found ebay... :D

[DA BIG ONE]

Perhaps, the lack of any real efforts by aftermarket sources to offer ugrades for the "turbocharger" on the 6.5 lies elsewhere?

I see plenty of offerings for ford, and cummins.

[DmaxMaverick]

Supply will meet demand. All the parts are out there. Someone has to put them together and offer it as a package. They are available. Just not as popular. Several DP advertisers offer them.

[eracers999]

Isnt what grape is trying to say is that decreasing drive pressure equals more exhaust flow, with a little less boost pressure more power is achieved. Heck i dont know, maybe he doesent either. If he had a school of thought on the issue he could spell it out.
Kent

[ 01-19-2005, 05:58 AM: Message edited by: Kent ]

[DmaxMaverick]

Kent

Grape is correct.

By decreasing exhaust restistance, less boost is required to produce the same power output. Less exhaust pressure means less effort to remove the exhaust gases from the cylinder. There is a delicate balance, and you need to select the turbine and compressor to suit your needs. Else, use an "off the shelf" turbo that has predictible results.

More boost does no good if it increases exhaust pressure to defeat it.

I really didn't want to get into this mess, but you guys are all arguing the same side.

[EWC]

Here's some number's , from Donaldson Exhaust , to go with the theory :

Navistar 6.9L 3000 RPM 170 HP 330 Intake CFM
Exhaust Temp and Flow = 1000* F and 892 CFM

Cummins 6BTA5.9 2500 RPM 180 HP 449 Intake CFM
Exhaust Temp and Flow = 900* and 1131 CFM

Detroit Diesel 16V-149TI 1900 RPM 1600 HP
5500 Intake CFM Exhaust Temp and Flow = 850 *
and 13343 CFM

[eracers999]

Dmaxmaverick:

I think i put into words what grape was saying. And you and i are saying the same thing. I dont find that hard to understand. And, im not on one side or the other.
Its about respect, thats all. So maybe my comment was innapropriate. But when you say that ( people on this board cant comprehend )and it is left to others to spell out what you are saying then obviosly they can comprehend. There are a lot of very intelligent members on this board, and the smartest one can learn somthing from the dumbest one.

[ 01-19-2005, 05:57 AM: Message edited by: Kent ]

[More Power]

Bigger turbo? You bet. Here's one Ken Klemm thought ought to do the trick. :D

http://www.thedieselpage.com/images/klemm.jpg


MP

[DA BIG ONE]

Well, I had forgot about pressure drop across my IC (B&D) so boost is higher than thought. Yep, still in a learning curve here.

Porting the turbine housing outlet should help some, anyone try this?

[DmaxMaverick]

ANYTHING you do to decrease resistance in the air tract will help, on either side. Just be careful not to change the geometry of the outlet in the process, unless that is your intent.

[gmctd]

Ok, MP - looks like I'm gonna have to modify the turbine housing-to-intake manifold bracket, and go with a cowl-induction hood, for a little more turbo-to-hood clearance, right? ;)

[grape]

I have a CFM riddle for you guys who like the CFM method. Figure out how it was possible for our last 356" craftsman truck engine to make 715 hp at 8900rpm with a 390CFM holley carburetor. CFM measurements without a test pressure are as useless as Penninsular's bogus dyno sheets. Displacement is displacement, CFM is air movement by either being sucked, or blown through an opening. For you to know what you have, you have to know how much force (psi or inches of water/mercury etc.) is being applied to the air that is either being blown or drawn through the opening. Saying that the 6.5 will only displace a certain amount is one thing, but it has nothing to do with the amount of air moved through the engine. If you have 200 hp worth of air at 12lbs of boost, 24 lbs with the same compressor doesn't give you enough air for 400hp, I promise.

There are so many factors with the CFM stuff........such as air has a weight which gives it inertia. So guess what happens when the piston is starting to travel up from BDC, while the intake valve is still open. Air continues to fill the cylinder untill the valve shuts or the force of the piston coming up overtakes the force of fresh charged air. Another factor is the negative pressure created in the combustion chamber just before the intake valve opens.....do you think that it is realistic to think that ONLY atmospheric pressure is pushing air into the cylinder when the intake valves first open on a naturally asprirated engine, while there is actually a vacum present on the backside of the vavle?

where I'm going with this, In our engines the test pressure for CFM or airflow is boost. Some guys have a boost pressure of 14 pounds, others have 8. Turbochargers do two things, 1 is a result of the other. 1st, they move air, 2nd they heat the air they are moving (or not moving) when out of the efficiency islands. Different turbos are capable of moving the exact amount of air at different boost pressures. Banks little red truck is a good example to look at, he is using the same math I am, He used 1 turbocharger designed for the specific power output of somewhere in the 700hp range while not needing more boost than the low 30's with the HX60. So how come all the dodge boys use two turbos and 90 pounds of boost to make 200hp less than Banks................LACK OF MATH.

[ 01-20-2005, 06:24 AM: Message edited by: grape ]

[gmctd]

Vacuum is a reduction in pressure from atmospheric pressure, grape - not an effect unto it self.

Otherwise, that engine would run in the total vacuum of outer space - which it will not.

30"hg is 15psi Barometric atmospheric pressure, or 0"hg vacuum.

0"hg is 0psi Baro is 30"hg vacuum.

15" vacuum inside the cylinder is 7.5psi inside the cylinder, with 30"hg 15psi outside the cylinder.

Pressure always seeks a lower level - fuel at 15psi in the carb is pushed out the jet, with a little help from a small pressure reduction across the venturii (that means more than one, as in the Dominator)into the 15psi air flow rushing in to fill the reduced 7.5psi pressure area above the piston.

An area in which the piston had "displaced" the air volume at TDC, and which the piston will very soon displace again, creating much higher than 15psi inside the cylinder - or, what's left of it at TDC, creating the effect known as compression.

This basic fact must be understood, or at least accepted, before we can relate 400CFM displacement at 15psiA, vs 400CFM at 15psiG.

Don't believe it?

Cut the valve stem outta one of your tires, and see how fast that 60psi tire pressure seeks the lower 15psi atmospheric pressure, outside the tire - will not require any vacuum.

Vacuum is a term for 'a reduction of atmospheric pressure'.

[ 01-20-2005, 08:41 AM: Message edited by: gmctd ]

[rjschoolcraft]

Originally posted by grape:
...do you think that it is realistic to think that ONLY atmospheric pressure is pushing air into the cylinder when the intake valves first open on a naturally asprirated engine, while there is actually a vacum present on the backside of the vavle? Yes!

Air moves from higher pressure to lower pressure. In a naturally aspirated engine, atmospheric pressure is what pushes the air through the valve opening. Now, the movement of the piston downward on the intake stroke quickly increases the volume in the cylinder, which creates a vacuum (or pressure lower than atmospheric). For a particular mass of air (or any gaseous substance), an increase in the volume of its container will decrease the pressure of the air (and its density). There is still a positive absolute pressure in the cylinder, it is just lower than the surrounding atmosphere.

Sorry to argue, but there's more than math to understanding how the world works... there's thermodynamics, physics, chemistry, aerodynamics, etc. Practical experience can get you part of the way there and is extremely valuable, but you also have to appreciate the laws of the engineering sciences. I don't make this stuff up.

[grape]

You guys have just proven that by your ideas and logic that an engine will never operate above the 100% efficiency level naturally aspirated, which is false. And still no explanation as to how 700+ hp happens through a 390cfm carburetor.

[rjschoolcraft]

I'm really sorry to break this to you...

Operating at 100% efficiency is impossible, let alone operating above 100% efficiency. There is something wrong with your equations and definition of efficiencey if you come up with greater than 100% efficiency for anything. The second law of thermodynamics comes into play here, and what you just said violates it badly. There are no known exceptions to the second law of thermodynamics. Lot's of folks have thought they found one, but none actually did when scrutinized further.

By the way, I would like a reply to the e-mail that I sent you. You have a really cool web site (if I found the right one).

[grape]

our race engines operate in the 120-125% efficiency range everywhere above 7200rpm. When we are on the dyno there is an airflow meter that sets above the carburetor and at any point beyond peak torque, there is more air going through the air meter than the engine displaces.
www.superflow.com (http://www.superflow.com)

[ 01-20-2005, 10:05 AM: Message edited by: grape ]

[rjschoolcraft]

Like I said, there is something wrong with your definition of efficiency. I didn't come up with this. The second law of thermodynamics has been around for a long time. There is absolutely no way that your engines are operating at the efficiency levels you claim. You would have to be creating energy out of nothing to do that...and that is impossible (violates the first law of thermodynamics).

I don't doubt that you've found a way to make power. But I'm certain that you are not operating above 100% efficiency. It's an indesputable fact.

[ 01-20-2005, 10:52 AM: Message edited by: ronniejoe ]

[nvmtnlion]

I work right across the street from Hunt-Spiller Globe Turbocharger and I will have to go take a picture of the turbo they have on the 18 wheeler trailer and post it here. Maybe that would be big enough?? tongue.gif

[gmctd]

A Flowmeter placed in the inlet path of a turbo pumping 15psi into a 400cfm engine will show much greater than 400cfm in order to make 15psi.

A Flowmeter placed in the intake path of the 400cfm engine will show 400cfm.

A Flowmeter placed in the exhaust path of the 400cfm engine will show much greater than 400cfm, because the Boost 15psiG is added to the original 15psiA, which then expands into atmospheric pressure as double the flow rate of the engine.

One cubic foot at 30psiA expands into two cubic feet at 15psia - the cubic foot is a rigid measurement, and does not change.

Only the content changes.

[ 01-20-2005, 03:21 PM: Message edited by: gmctd ]

[David Brady]

Grape,
I see what you are saying about the dynamic forces at work in a high speed gas. So... What pressure differential is used to measure that 390 CFM Holley? These static gas type illustrations we've been thinking about are good at certain things, but not every situation. I'm still looking for the hot tip on the turbo, and I'm watching the others who have time to experiment. I still am wondering about the exhaust side restriction at high rpms. This is the first diesel I've seen that has this "power" range of 1500 - 3500.

[Peter J. Bierman]

I have to go with grape, but I looked up the right way to call it and it's called volumetric efficiency.
This can be more then 100% but to do so you would need cam profiles that are allmost impossible with diesels couse off the lift and duration needed.Next to that you would need high RPM's to get the high air flow that you can gain from the mass.
Since we use a turbo to push the air in we can get more then 100% at 2000 RPM :D
Thing with turbos ( or any engine component ) is that it's disigned for certain RPM to work at it's best, so there allways be compromise.
A 750 HP car engine will not be so driveable on the street as a 150 HP low torque engine, which would offcourse look stupid at the race track tongue.gif
Just think what you want and then start looking for equipment to reach that.
The LLY Dmax turbo with variable pitch would be a good place to start :D

Peter

[rjschoolcraft]

Now that I read Grapes post again, I can see that he implied volumetric efficiency. However, I read overall efficiency, which includes thermal efficincy and mechanical efficiency as well. All of my comments are directed at overall efficiency and probably do not apply here.

And yes, there is a ram effect when air moves at high speed that will over charge a cylinder from momentum and +100% volumetric efficiencies can be achieved...again because of the definition. Much like torque converter efficiency, which is often defined as the output speed over the input speed. When decelerating the turbine is running faster than the pump, resulting in plus 100% efficiencies.

The motivating force for the filling of a cylinder in a naturally aspirated engine is still atmospheric pressure, but you can get it moving fast enough that momentum plays a role.

I apologize for my misunderstanding of what we were talking about and wish that Grape had clarified it sooner.

[grape]

I get lost in my own little world sometimes. smile.gif

[dieseldummy]

The part about banks race engine making 700hp with low boost is partially due to the fact that they ported and polished every aspect of the head. If I remember correctly they even made a custom intake plenum for better flow. They can make 700 hp on 30lbs of boost because the 30 lbs is made cool and efficiently and doesn't face much restriction going into the engine. The guys who run 90lbs to get the same results are adding the 60 lbs to overcome some restrictions in their system. It has also been said that banks over advertises their products... This is my weak understanding of their project at least. If I had the time or money to keep messing around with turbo's I would, but I have found what currently works for me and it makes me happy as a clam. smile.gif When the rest of you who are more mathematicly inclined figure this out I think we'll all be better off for it. :cool:

[David Brady]

Has anybody researched the garratt variable nozzle turbo for this application? Where can I find more information on this - is it expensive?

[Peter J. Bierman]

I am not sure about the garrett you mention but usualy on everyting variable you need a way to control it, I think that would be the hard part.
Same with variable intake runner lenght, would be cool to have massive low end torque and still get a lot high RPM horses.
Physicaly it's not that hard but the control would be tought :confused:

Peter

[rjschoolcraft]

Originally posted by grape:
...you can move more air through the same engine WITH LESS BOOST, with a different compressor wheel. This statement simply is not true.

Consider two different trim configurations of T04B compressors: H-3 and V-1/V-2. Maps for these are available at Turbonetics web site. (http://www.turboneticsinc.com/compressor.html?action=display) If our 395 CID (6.5 liter) engine is running at 3000 rpm and 15 psi cdp (compressor discharge pressure ), the pressure ratio will be 2.06 (assuming .5" Hg depression at inlet) and air flow will be 35.2 lb/min. This is true no matter which trim is used. The difference? The H-3 trim will do it at about 75% efficiency while the V-1/V-2 trim will do it at about 72% efficiency.

Now consider two different engine speed points. At 3000 rpm and 19 psi cdp, the pressure ratio is 2.33 and the flow is 39.8 lb/min. At 3500 rpm and 15 psi cdp, the pressure ratio is 2.06 and the flow is 41.1 lb/min. Here the compressor... [i]the same compressor... can move more air at a lower pressure ratio because the engine, or downstream pump, is running faster!

What we have here is a dynamic compressor (or pump) feeding a positive displacement compressor (or pump). Operating conditions of one affects the operating conditions of the other and vise versa.

Flow through a dynamic compressor can be increased two ways. If you increase the engine speed while keeping pressure ratio constant, you will move horizontally to the right on the map and increase flow. If you increase the pressure ratio while keeping engine speed constant, you will move diagonally up and to the right on the map and increase flow.

The whole job of matching a compressor to an engine is a matter of calculating the various speed vs. pressure ratio conditions that you want to run, then selecting a map that will encompass them all. The flow and pressure ratio are established independently of the particular impeller/housing combination.

Consider two other points: 1) 2000 rpm and 12 psi cdp; 2) 3500 rpm and 12 psi cdp. At the first condition, for our 395 CID engine, the pressure ratio is 1.85 and the flow is 21.2 lb/min. At the second condition, the pressure ratio is 1.85 and the flow is 37.0 lb/min. A T3 50 trim compressor can operate at the first point and do so with about 71% efficiency. However, it cannot even come close to the second point because it chokes at about 27 lb/min. It physically is not large enough to do the job. On the other hand, a T76 compressor cannot flow the first point because the compressor will surge. This compressor can flow the second point at about 76% efficiency.

Hopefully this will help to illuminate this discussion. Spend some time and study the maps referenced above. There are several "calculators" available to crunch the numbers. I would also recommend Hugh MacInnes' book Turbochargers. All the basics are laid out there.

[DA BIG ONE]

Originally posted by ronniejoe:
</font><blockquote>quote:</font><hr />Originally posted by grape:
...you can move more air through the same engine WITH LESS BOOST, with a different compressor wheel. This statement simply is not true.

Consider two different trim configurations of T04B compressors: H-3 and V-1/V-2. Maps for these are available at Turbonetics web site. (http://www.turboneticsinc.com/compressor.html?action=display) If our 395 CID (6.5 liter) engine is running at 3000 rpm and 15 psi cdp (compressor discharge pressure ), the pressure ratio will be 2.06 (assuming .5" Hg depression at inlet) and air flow will be 35.2 lb/min. This is true no matter which trim is used. The difference? The H-3 trim will do it at about 75% efficiency while the V-1/V-2 trim will do it at about 72% efficiency.

Now consider two different engine speed points. At 3000 rpm and 19 psi cdp, the pressure ratio is 2.33 and the flow is 39.8 lb/min. At 3500 rpm and 15 psi cdp, the pressure ratio is 2.06 and the flow is 41.1 lb/min. Here the compressor... [i]the same compressor... can move more air at a lower pressure ratio because the engine, or downstream pump, is running faster!

What we have here is a dynamic compressor (or pump) feeding a positive displacement compressor (or pump). Operating conditions of one affects the operating conditions of the other and vise versa.

Flow through a dynamic compressor can be increased two ways. If you increase the engine speed while keeping pressure ratio constant, you will move horizontally to the right on the map and increase flow. If you increase the pressure ratio while keeping engine speed constant, you will move diagonally up and to the right on the map and increase flow.

The whole job of matching a compressor to an engine is a matter of calculating the various speed vs. pressure ratio conditions that you want to run, then selecting a map that will encompass them all. The flow and pressure ratio are established independently of the particular impeller/housing combination.

Consider two other points: 1) 2000 rpm and 12 psi cdp; 2) 3500 rpm and 12 psi cdp. At the first condition, for our 395 CID engine, the pressure ratio is 1.85 and the flow is 21.2 lb/min. At the second condition, the pressure ratio is 1.85 and the flow is 37.0 lb/min. A T3 50 trim compressor can operate at the first point and do so with about 71% efficiency. However, it cannot even come close to the second point because it chokes at about 27 lb/min. It physically is not large enough to do the job. On the other hand, a T76 compressor cannot flow the first point because the compressor will surge. This compressor can flow the second point at about 76% efficiency.

Hopefully this will help to illuminate this discussion. Spend some time and study the maps referenced above. There are several "calculators" available to crunch the numbers. I would also recommend Hugh MacInnes' book Turbochargers. All the basics are laid out there. </font>[/QUOTE]Hello, perhaps you can post a chart for the 6.5
showing VE up to 3,500 rpms w/o boost, then show VE in 5 lb increments up to say 25 psi so everyone can better understand this?

[gmctd]

Couldn'ta said it better, myself, rj........... ;)

If flowrate of compressor is greater than flowrate of engine, excess flow rate will stack up in intake as pressure, and vise versa (without all them confusin' numbers!)

[Cowracer]

I am an electrical engineer. I can move the little electrons from one place to the other.

I am not so good on fluid dynamics.

But it seems that any turbo will be a compromise. Any unit that frees up exhaust back pressure will make boost slower. Any unit that makes boost quickly will increase you exhaust backpressure dramatically.

So, the ideal would be a series-parallel twin-turbo setup with GM4's. Or perhaps a big honking un-wastegated turbo, with compressed air jets to increase spoolup rate (like WRC rally cars of a few years ago)

There. Problem solved. I thought of it, now someone else will have to make it. I cant do it all myself :D

Tim

[rjschoolcraft]

A few months back, I was contemplating these issues. Thought, "What if we added an electric motor to assist the turbine at low engine speeds and exhaust pressures. Could have near instant boost at low speed and let the exhaust pressure take over at high speed."

Decided, "Naw, it wouldn't be practical."

Holset is working on this very technology (see page 11 of the HTi magazine (http://www.holset.co.uk/pics-related/3-media/3-1-magazines/HTi-issues-3.pdf) available on their website). In fact, plan to use the motor as a regenerative electrical power source and eliminate the alternator.

Always a day late and a dollar short.

[grape]

with one particular engine we made 540ish power with 17 pounds from a 60-1 with the air fuel ratio at 12.2 across the board. Same engine with no changes other than a T76 at 12 pounds required 50 pound per hour injectors instead of 42's to keep the air fuel ratio the same without having 100% duty cycle on the injectors. (more air coming from somewhere even though boost is lower right?) This engine lasted for about 30 minutes worth of tuning on the dyno before the block split in half. The last run before it broke (which we knew it would) it made in the high 650's.

so we had 100 more hp and 5 lbs less boost. Everybody post up real world situations like this of your own, with your own experiences of changing turbo's around on the same engine. Maybe only the engines down here in texas that I know of react like this.

[gmctd]

Has to do with air velocity at 8000rpm, and Boost temperature.

Be really handy, knowing engine displacement and rpm, involved in those posted numbers...........

We're dealing with 397cuin, 3700rpm max, with 347swept\displaced cfm at 3000 naturally aspirated rpm

One 303cuin engine you mentioned was flowing 695cfm at 7700rpm - highly unattainable in any of the 6.5 scenarios, wouldn't you think?

Flowrate in cfm is a highly important figure, in figuring lbs\hr flow capability in any engine comparo.

If flowed cfm rate - swept volume - cannot be increased, pack more oxygen in each flowed cubic foot with pressure - Boost.

[grape]

306 cubic inches made peak power at the rev limiter 6200 with both turbos, one curve was just above the other one at every point on the graph with lower boost. All runs compared were from 3000 rpm to 6200. Both turbos were at their respective max boost setting......12 with the 76 and 17-18 with the 60-1.

[gmctd]

Can we assume charge-air cooling?

[grape]

same intercooler used with both turbos.

[gmctd]

Good - what about Intake Air Temperature at\in the intake manifold - post c-a cooler - for 12psi run and 17psi run?

And, I don't suppose y'all were monitoring Exhaust(back)Pressure in the manifold\turbine? :cool:

[rjschoolcraft]

Here are compressor maps plotted for the conditions you've presented so far: Compressor Maps. (http://www.schoolcraftpowertrain.com/CompressorMaps/GrapeComparison.pdf)

These maps show that if boost was held constant during the accel, one of the points cannot be run because it's left of the surge line. I assume that boost built during the accel, but that was not reported.

The points, from left to right on both maps, are for 3000, 4000, 5000, 6000 and 6200 rpm engine speed respectively.

Pressure ratio for 17 psi boost (19 psi cdp) is 2.33 while pressure ratio for 12 psi boost (14 psi cdp) is 1.99 for standard day conditions of 59F and 14.7 psi ambient.

Air flow for the 17 psi case is 66.9 lb/min and for the 12 psi case is 57.3 lb/min.

Fuel flow for the 17 psi case is 5.48 lb/min. Assuming 80% injector duty cycle, the required size is 51.4 lb/hr. Fuel flow for the 12 psi case is 4.69 lb/min. Again, assuming 80% duty cycle, the required injector size is 44.0 lb/hr.

This is using a specific gravity of .735 for gasoline and the stated air/fuel ratio of 12.2:1.

Now, if the conditions changed between the runs the following could have happened.

If the 60-1 was run on a hot day (95F) and low barometric pressure (28.70" Hg):

Pressure ratio for 17 psi boost (19 psi cdp) is 2.39 and the air flow is 61.2 lb/min. A 42 lb/hr injector running at 90% duty cycle could flow the required 5.01 lb/min to give a 12.2:1 air/fuel ratio.

If the T76 was run later on a cooler day (70F) of high barometric pressure (30.97" Hg):

Pressure ratio for 12 psi boost (14 psi cdp) is 1.95 and the air flow is 57.2 lb/min. A 50 lb/hr injector running at 72% duty cycle could flow the required 4.69 lb/min to give a 12.2:1 air/fuel ratio.

You didn't report the ambient conditions, but this is one scenario that could explain the differences that you observed.

Another point of observation: the 6200 rpm point on the 60-1 is very near the choke line. Barometric conditions could have pushed the operating point beyond the choke line meaning that the compressor could not actually deliver the flow. If this happened, you should have seen boost drop some if you stayed at the 6200 rpm point for very long.

Looking at the T76 map, there should have been a lot more pressure ratio available at 6200 rpm. Had you used that, you would have blown the block apart much sooner. ;)

Tell me what I've missed here.

[ 03-04-2005, 01:25 PM: Message edited by: ronniejoe ]

[DA BIG ONE]

I still think a chart would help, start @ 100% VE show cfm up to 3,700 rpms like in 500 rpm increments, then boosted in 5lb increments, up to what would be considered practial for the 6.5TD

Perhaps, real world we are looking at only 70% VE, just guessing here.

The following site will give ya all an idea of what I am talking about relating to chart:
http://www.stealth316.com/2-turboguide.htm#c

[rjschoolcraft]

At present, I have no data to determine volumetric efficiency at different engine speeds. I have assumed 80% for all the calculations. I've used 65% compressor adiabatic efficiency and 80% intercooler efficiency. These are reasonable. While the compressor varys between about 65% and 75% in most cases, I've done several comparison calculations and found the effect to be fairly small. So I left the compressor efficiency at 65% for these calculations.

The maps in the link that you referenced would not look much different if the VE had not been changed. As I said earlier, constant engine speed curves are straight lines running diagonally up the map as pressure ratio increases (as shown in the referenced maps).

There is one sentence in that write up in the link that I want to quote here. "At a given RPM and at the same plenum air pressure and temperature, the same amount of airflows regardless of which turbo is used."

The point I made earlier about varying ambient conditions is specifically why the Standard Conditions were established in the first place. If you'll notice, most maps (if they're done right) have corrected airflow on the x-axis and have corrected rotor speed lines plotted on the map. These corrections bring everything back to standard day conditions so that accurate comparisons can be made. I suspect that neglecting these corrections is what has led grape to his conclusion.

I don't know if you can tell, but I've spent a lot of time thinking about this and running calculations over the past few weeks. Grape's comments come from a fairly good level of experience and I've worked hard to square them with theory. If he's still following this thread, I hope we can both come away more knowledgable. I know I have.

[ 03-04-2005, 03:59 PM: Message edited by: ronniejoe ]

[gmctd]

So - what you're saying is the T60 was producing much more flowrate than engine required, which resulted in greater Boost than required, which resulted in higher IAT and lower density air charge, and the extra turbine power needed to produce that higher Boost, resulted in higher exhaust (back) pressure, choking flow?

Increasing the compressor fan diameter resulted in actual required Boost at lower rpm, which reduced the turbine power required to make the Boost, thereby lowering the exhaust (back)pressure, with resultant increase in overall engine flowrate?

See - I knew something hadda change - either that, or snake oil really works. ;)

Now, how do we apply that to an engine that only makes ~3000rpm, where workable rpm range is 1200 to ~3000-3500, with most folks prefering to keep it down around 2200?

And btw - most Diesels make ~100% volumetric efficiency, normally aspirated at 15psia.

Simply add a turbo and 15psig Boost, and volumetric efficency goes up to ~200%.

Gasser VE formulas don't exactly apply, here - you get to fudge, a bunch.

[DA BIG ONE]

Originally posted by ronniejoe:
At present, I have no data to determine volumetric efficiency at different engine speeds. I have assumed 80% for all the calculations. I've used 65% compressor adiabatic efficiency and 80% intercooler efficiency. These are reasonable. While the compressor varys between about 65% and 75% in most cases, I've done several comparison calculations and found the effect to be fairly small. So I left the compressor efficiency at 65% for these calculations.

The maps in the link that you referenced would not look much different if the VE had not been changed. As I said earlier, constant engine speed curves are straight lines running diagonally up the map as pressure ratio increases (as shown in the referenced maps). Anyone here willing to do a chart for our motors, say at 75%VE?

[rjschoolcraft]

OK.

Here's a map of a turbocharger compressor that very closely approximates a GM-4. I have stripped the numbers off of it because I do not have permission to share them in the public domain...and I will not get it.

Compressor Map (http://www.schoolcraftpowertrain.com/CompressorMaps/Map.pdf)

These calculations are based on 80% VE, 80% IC efficiency and 65% adiabatic compressor efficiency. I used 85F ambient conditions and 29.92"Hg barometric pressure. The diagonal lines are 6.5 TD engine speed lines with varying pressure ratio. This should give you an idea of what the map looks like.

At some point, I could plot this data again on a publicly available map, but I don't have time at the moment. I've spent too much time on this as it is, but it matters to me to get this right.

[DA BIG ONE]

Good man Ron!

[rjschoolcraft]

Originally posted by gmctd:
So - what you're saying is the T60 was producing much more flowrate than engine required, which resulted in greater Boost than required, which resulted in higher IAT and lower density air charge, and the extra turbine power needed to produce that higher Boost, resulted in higher exhaust (back) pressure, choking flow?

Increasing the compressor fan diameter resulted in actual required Boost at lower rpm, which reduced the turbine power required to make the Boost, thereby lowering the exhaust (back)pressure, with resultant increase in overall engine flowrate?

See - I knew something hadda change - either that, or snake oil really works. ;) Not exactly what I was trying to get across.

The 60-1 compressor is a pretty good match for the engine until you get to about 5500-5800 rpm. After that, you're running very close to the choke line. The T76 is actually too big... You flirt with surge at lower rpm and don't come close to its max flow capacity at 6200 rpm.

I believe, unless Grape shares some more data, that ambient condition changes explain the observations he made.

There is something to the argument of improved adiabatic efficiency of the bigger unit, as GMCTD said, that helped it produce more power. But I don't think it can explain everything.

As I said before (and quoted another source as saying), the positive displacement pump (our engine) operating speed is what dictates the mass flow rate for a particular manifold pressure and temperature. All of the applicable equations point to this fact.

[rjschoolcraft]

I've run a few more numbers.

Combining the effects of the estimated ambient changes with the adiabatic efficiency read from the maps, the flow for the 60-1 at 6200 rpm is 60.3 lb/min and the flow for the T76 is 57.9 lb/min. This brings them fairly close together.

[gmctd]

But, would not high exhaust backpressure, way over that required to power the turbine to produce that pressure in the manifold, would that not reduce desired mass flow?

Lowered ebp would explain increased flow with lower Boost at same rpm, as happens in our trucks with a Holset, or some such larger turbo.

Little or no low rpm spoolup, because of reduced exhaust pressure, but increased power at hiway speeds and upper rpm, where exhaust volume and energy is high.

Or, not?

More Power ran into this while testing the 18:1 300hp engine in the Project Truck, using a GM-8, and all the goodies.

[DA BIG ONE]

Originally posted by gmctd:
But, would not high exhaust backpressure, way over that required to power the turbine to produce that pressure in the manifold, would that not reduce desired mass flow?

Lowered ebp would explain increased flow with lower Boost at same rpm, as happens in our trucks with a Holset, or some such larger turbo.

Little or no low rpm spoolup, because of reduced exhaust pressure, but increased power at hiway speeds and upper rpm, where exhaust volume and energy is high.

Or, not?

More Power ran into this while testing the 18:1 300hp engine in the Project Truck, using a GM-8, and all the goodies. Then 2 properly sized and smaller turbos (biturbo) would be the answer for increased power the 6.5 at all rpm ranges, or?

[rjschoolcraft]

Remember, we have a positive displacement pump in front of the turbine. It will push the mass through there and the turbine will spin faster with increasing back pressure... until sonic velocity is reached at the nozle throat. At that point, the flow is choked and no more may pass, period.

Increasing engine speed here will dramatically increase backpressure with no resultant increase in flow through the turbine and no more boost. In fact, as engine speed increases, boost pressure will drop, because the compressor will not turn any faster and the engine will begin to pull down the plenum. Since there is very little valve overlap, you likely won't get much reversion. This will continue until something bursts if engine speed continues to increase, or an equillibrium may be reached and the engine will not speed up any more.

The same problems exist with two turbos as with one. You just base the sizing on half the engine displacement and flow.

[Peter J. Bierman]

I run a twin turbo setup for two years now and yes it's close to perfection; fast spoolup and low rpm boost.
I do not have any hard data but this works best at low and mid RPM, and that's were we use them right? :D
I am investigating ways to get more air in and used gasses out.
I will do messurements on all sides and let you know the results.

Peter

[grape]

so let me get this straight.......a bunch of guys who have never done any of this stuff with their own hands are telling me that what I've done numerous times didn't happen. Of course nobody liked it when I proved that Penninsular diesel was lying to potential customers on their bogus dyno sheets, so what should I care what yall think.

[rjschoolcraft]

Grape,

I've done things with my hands that you will never be able to do, sir. I've designed machines that you cannot even understand. Machines that go straight up (helicopters and supersonic fighter jets). Machines that put 25,000 hp through a bevel gear set. Machines that put 13,000 hp through a single stage planetary set. Transmissions for bulldozers. I was building engines before you were born. Have you ever been issued a patent? Have you ever run a backhoe? A bulldozer? A scraper? A grader? I was operating farm machinery (doing the work of a full grown man) when I was 10 in 1975. Have you ever built an automatic transmission? Wait, I know the answer to that one. Yeah, you've gone around in circles on a race track. Cool.

Has Caterpillar ever called on you to help them solve problems that they can't? Asked you to travel to Europe because you have expertise that they don't? Has Rolls-Royce ever called on you to help them solve problems because of your special expertise?

Guess what kind of compressor is used on the Allison Model 250 Series IV helicopter engine. Don't know? It's a single stage centrifugal...same idea, but much higher technology and capability than our dinky little turbo chargers. Guess what the takeoff airflow is. Don't know? 6.1 lb/sec...that's lb/sec. Here's some math again, that's 366 lb/min. The pressure ratio is 9.2:1. Have you ever worked with compressors that can do that? What's the power to weight ratio of the engines you're so proud of? I bet it can't touch 2.97 HP/lb. That's what the little 274 lb engine made that I've worked on... with my hands and my computer.

I think we can dispense with the "never done any of this stuff with their own hands" crap, at least in my case.

What I'm telling you is that you've missed an observation. Did you account for ambient conditions? Answer the question. If you don't care to expand your knowledge base and your horizons, so be it. Your only response so far has been to ridicule, insult and attack.

You talked about math earlier... Where's my math wrong? I've presented calculations, compressor maps and data to support my position. If you want to continue in your mistaken understanding, fine.

I didn't get to be the best at what I do by accident. Yet, I know that there are things I need to learn. You have much to learn as well, young man.

[Barry Nave]

OUCH :( :rolleyes:
Think I'll move on to another tobic and not go here :confused:
Oh the things that make us men go BOOOOOOOOM :confused:

[gmctd]

No one is indicating that you may have a predilection for prevarication, grape, nor a propensity for persevering in that particular endeavor.

However, tossing out numbers to prove a point requres tossing out ALL the numbers involved in the claimed results.

To wit -
the small turbo produced 17-18psi Boost at 6200rpm
the larger turbo produced 12psi Boost at 6200rpm

This indicates the smaller turbo was puffing into some form of restriction - and I quote me - when the flowrate of the compressor exceeds the flowrate of the engine, the excess flow stacks up in the intake as pressure.

Either the throttle plate(s) was not fully perpindicular to intake flow, or exhaust back pressure was much higher than expected.

Either scenario results in reduced flowrate, with reduced mass thruput - the higher Boost with the smaller turbo is proof of this.

Imo, you should have been monitoring exhaust pressure in the turbine.

The higher Boost pressure would also result in higher Boost temperature - high temp air charge is low density air charge.

You were not flowing as much mass at 18psi as at 12psi.

Air-over charge-air cooling is only as effective as charge-air temperature vs ambient temperature delta.

Water-cooled heat exchanger would be more effective, with repeatable results, if water temperature is controlled, say to world standard 60deg.

Imo, you should have been measuring Intake Air Temperature in the intake plenum.

Or, if you were, those numbers should also have been posted.

ronnejoe stated, and proved, the smaller turbo was stressed at 6200rpm, but was more suited to lower rpm ranges, indicating it would be best suited to street applications, where dynamic range is ~3000rpm to 6200rpm.

He also stated, and proved, the larger turbo was much more efficient at 6200 rpm, but less efficient at lower rpm ranges, indicating it would be best suited for racing application.

What is required, then, to prove or explain your results, are specific numbers indicating ambient conditions - temperature, humidity, Baro - and volumetric efficiency - input-output pressure differential - for each of the indicated runs.

I do not always understand the numbers, but I do understand the concepts, absolutely - thus, you get the simple, practical explanation.

Which is what I understand.

Now - what say you?

[JoeyD]

Ron, Don't break your arm patting yourself on the back. :D

[JohnC]

OK, everyone, take a time out...

[JoeyD]

That sounds about right. In the end we are all on the same side here. ;)

[rjschoolcraft]

Originally posted by Joey D:
Ron, Don't break your arm patting yourself on the back. :D Fine. I've specifically avoided writing anything to attack the young man. I tried to be gentle. I tried to be humble. I've tried to apply sound scientific principles to this discussion. He referred to "math" previously and said that I (among others) didn't know how to "do math." Funny, when the math doesn't favor his opinion, the personal attacks come out and he says I've "never done any of this stuff" and have no business discussing it.

At that point, the arrogance of the young man elicited a rather angry response, which I thought, and still think, was appropriate. Maybe it wasn't, but we're all human and occasionally insults can go too far. If he wants to believe that "you can move more air with less boost with a different compressor wheel," well, that's fine. That doesn't make it a scientifically provable point nor even true.

Going around in circles on a race track doesn't make you an expert at mechanical systems. It makes you good at going around in circles.

I do have specific experience in this field at a level of technology that he cannot even fathom, yet he can flippantly say it's worthless compared to his dizziness. That was simply more than I was willing to take.

I made my choice, now I'll live with the consequences; whatever they are.

[JoeyD]

To be honest Ron, I was laughing while reading. Thats why I wrote what I wrote.

[DA BIG ONE]

So, it seems the variable nozzle compressor would be best for our 6.5 motors, and 300 hp would be a safe level of power w/o having to build the bottom end, or?

[gmctd]

Ford uses variable vane for the PowerStroke 6.0, but seems no one has tried it yet.

Far as the 6.5 bottom end, the only possibly safe build-up is to start with the splayed mains setup, have the crankshaft balanced, tuf-trided, polished, don't grind the journals in any manner which will dimensionally reduce the rolled fillets, which strengthen the cast-iron crank.

Got to balance all this with how long before you convert to DMax or Cummins......... ;)

[Mark Bajus]

not to hi-jack this thread, but can someone point me to the one where the Penninsular dyno sheets were shown to be incorrect?

[rjschoolcraft]

It wasn't Penninsular...it was Marine Diesel USA. The charts they have posted now appear to be correct. I don't know about the previous ones. I never saw them.

[Jim P]

Here is a thread about the dyno sheets but I don't know if the dyno sheet itself was ever posted.

dyno sheet thread (http://forum.thedieselpage.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=006455#000000)

[rjschoolcraft]

Well, I never saw that thread. I only saw the one where Marine Diesel USA was discussed.

[Cowracer]

RJ and Grape:

Criminy!

I still love both you guys, but what's next? Are you gonna start comparing penis sizes? :rolleyes:

The worst sin of an engineer is to think that he is better than anyone else. If you think you are the best, you stop listening to the other guy.

If you stop listening, you stop learning. And an engineer that stops learning is just about useless. I have fired more than a couple engineers that think the shop personell are "beneath" them and refuse to listen to them, just because they are engineers, and the shop guy isn't.

It's okay to disagree, and even argue, but lets keep it civil. Make your point, present your data, and trust the rest of us to be smart enough to follow along.

This is not a compitition. Nobody gets bonus points for being right.

thanks!
Tim

[rjschoolcraft]

Originally posted by Cowracer:
RJ and Grape:

Criminy!

I still love both you guys, but what's next? Are you gonna start comparing penis sizes? :rolleyes:

The worst sin of an engineer is to think that he is better than anyone else. If you think you are the best, you stop listening to the other guy.

If you stop listening, you stop learning. And an engineer that stops learning is just about useless. I have fired more than a couple engineers that think the shop personell are "beneath" them and refuse to listen to them, just because they are engineers, and the shop guy isn't.

It's okay to disagree, and even argue, but lets keep it civil. Make your point, present your data, and trust the rest of us to be smart enough to follow along.

This is not a compitition. Nobody gets bonus points for being right.

thanks!
Tim Thanks. That is the specific philosophy that I live by. The guys on the manufacturing floor at Allison Plant 5 know me and trust me for that very reason. I'm just a dumb old farm boy who happens to have a degree. The attack came from the other direction...I merely tried to set the record straight. I never accused anyone of lying either. If I thought I was above him, I wouldn't have spent four weeks doing calculations in my spare time to generate the data. I would have just made a pronouncement and left it at that.

I have tried to contact Grape off-line to work this out. He will not respond. There is nothing I can do about that. I'm willing, and able, to forgive and forget, but I will not be ashamed of the truth.

As for the other issue, mine's not very big, so I rarely try to compare.

[ 03-09-2005, 02:26 PM: Message edited by: ronniejoe ]

[Marty Lau]

Sheese, I followed along with some of this and even understood parts of it. I just don't understand how more power with less boost, it goes beyond my simple basic mind. From my basic understanding to produce power first you need to burn more fuel. To burn more fuel you need more O2 for combustion. With your intake it will only allow a certain volume (CF) of O2 per intake stroke all this equates to oxygen molecules. They only way I can see to increase the oxygen molecules in a given volume is to increase the pressure, ie more boost. So what am I missing how do you get more O2 in a given volume with lower pressure by changing Turbos???? :confused:

I'm also with Tim on this bubble bee's do fly in reality but not on paper. :rolleyes:

[JohnC]

Having made no attempt at all to follow the math, even though I may be able to, I'd like to throw out the following. Maybe I'm completely off base, or maybe I really missed something along the way. My attention span isn't what it used to be...

Anyhow, imagine a turbo producing "more' boost, say 20 psig for sake of argument, that developes say 30 psig of backpressure. This back pressure will surely affect cylinder scavenging and could even force exhaust gasses back into the intake plenum during valve overlap.

Now, imagine a different turbo, producing less boost, say 14 psig, with say 12 psig of backpressure. Isn't it possible that the second setup could flow more pounds of air than the first, even though the manifold pressure is lower? More air -&gt; more fuel -&gt; more power, no?

Problem as I see it is that the difference between the two turbos would more likely be in the turbine wheel, not the compressor wheel...

[gmctd]

Simply stated - and I'm simpler and older and maybe more senile than ya'll maybe are, so bear with me. ;)

The exhaust gas turbine is a motor, which develops horsepower to run an air compressor.

Compressing air requires power - the more pressure required, the more air required, the more power required, the faster the turbine must spin to develop that power.

More required power is due to increased resistance of high volumes of air being converted into pressure.

This increased resistance is felt in the turbine wheel, resulting in turbine wheel being more difficult to turn, which requires more exhaust pressure to turn turbine wheel.

The result is higher exhaust back pressure against more resistance - for higher Boost pressure - more resistance.

By running a larger compressor wheel on same turbine wheel, required lower Boost could be developed at lower turbine rpm and with lower ebp, with resultant increased flow-thru.

The ~18psi with the smaller wheel indicated a restriction to flow-thru, as well as higher Intake Air Temperature, which would reduce intake air density.

Reducing ebp and increasing intake air density would result in more power at same engine rpm, with lower Boost.

Gm-X series turbos on 6.5 engines are excellent daily example of the problem.

[ 03-08-2005, 03:28 PM: Message edited by: gmctd ]

[Cowracer]

In simple terms...

BOOST AIN'T FREE!

It takes power to make boost.

Say a given N/A motor makes 100 hp. If you had an electric motor driving a blower pumping 6 lbs boost into the engine, it would then make 125 hp. Ramp the electric driven blower up to 10 psi, and this engine would make 135 hp.

So far, so good. But install a turbocharger instead of the electric blower. The engine exhaust gases drive the turbine. The cylinders push out the gases. It takes engine power to push out the gases against the restriction that is the turbo.

So back to our theoretical 100HP N/A motor. Now with a turbo running at 6lbs, it still makes 125 HP BUT it takes 10 hp to run the turbo. Net output of the engine is now 115 hp

If we set the turbo to run at 10 lbs, the engine will still 'make' 135hp, but lets assume its a really in-efficient turbo (GM-4 anyone?) for the application. It takes 25 hp of engines output to make the 10 lbs of boost. Net engine power is now 110HP.

I know that these numbers are theoritical, but that is exactly how a mis-matched turbo can cause an engine to produce less NET hp with more boost.

Tim

[Marty Lau]

okay makes more sense now , I knew engine driven superchargers ran into this problem but I never thought about Turbos since your pushing the exhaust out anywho, but it does make sense that it would cause back pressure to turn hence power.

[patrick m.]

im certainly not an engineer, just a mechanic who now tries to run a small company.

being a mechanic (automotive) has led me to performance, started as a teenager, thought i out grew it till i found this place ;) . All of us have a "butt dyno", we know there is some kind of scientific explaination for everything, (we're talking autos), most of us enjoy getting the explaination. We come on a problem, find the problem, repair the problem, but do not fully understand the problem.
we know what was wrong, what "fixed" it, but dont know the details of what failed, you develope a skill at this (at least i have).
See i was "trained" to be a mechanic, went to school for it, had to apprentice at a local dealership to graduate.
They dont teach what makes things work, they teach what makes things work again....the repair.


I am a very good mechanic, thats why i do what i do, i stil cant explain alot of things, and i dont fully understand alot of things, cant, dont need to, dont have time to , gotta get the car fixed and out the door. Why did that alternator fail? dont know, check this, this, and this, if all o.k. replace it. Get the car back to the customer.

This is my world, and i expect the same for many others. Capitolism demands it. If you cant do it now, someone else can!

The engineering world is different i would imagine. The most important factor is WHY. instead of NOW.

I'm sure Grape is in the NOW world, with me. Doesnt matter WHY, all that matters is more power, other people in his group were responsible for the WHY. His job was to "fix this", "set up that", "run this one". and record everything, which he did.


i personally long for the WHY. like "why do the posts fall out of Delco batteries ETC". "Why does the EGR path stop up on a 4.6L ford"? Too late now, my path is set. Repair it, and get it out the door! If you've read many of my posts, you will know i use commas a lot and i look for posts by GMCTD, and RJ. Because they always have the "WHY".

Grape, if you read this, realize no one doubts you are an accomplished person, we can see that. everyone just wants to know more about what intrests them. If you cant explain it, explain that and ill bet these guys will figure it out, and explain it for all of us :cool: