Boost Pressure Vs. RPM [Archive] - TheDieselPage.com Forums

Amianthus

04-30-2002, 09:27

Okay, here's the deal. Boost is not a function of RPM. Let me repeat that. BOOST IS NOT A FUNCTION OF RPM!!!
The turbine section of the turbo-charger is not a pinwheel and blowing air across it is not what makes it spin. What makes it spin is heat. Heat from the combustion process. Heat from the expansion of gasses as they pass through the turbine blading.
If you were to look at two thermocouples, one pre and one post turbo, you would see that there is a differential temperature across it. It can be more than a 500 degree difference. You aren't losing that heat to ambient. The turbo is taking the thermal energy rejected from the engine and transforming it to rotational mechanical energy. That rotational mechanical energy is used to drive the compressor to make boost. That is how boost is made.
Now it stands to reason, based on what I said above, that the only way to get the turbo to make more boost is to make more heat. How do you make heat in these engines? By adding more fuel. You add more fuel by pressing down on the throttle. Make sense?
I have been at 1500 rpm and made 50 psi boost. I've also been at 3300rpm and made just 15 psi boost. There isn't any correlation between the two.
So saying that you don't have boost at a certain RPM really doesn't mean anything. Now if you have it floored, and you aren't making boost, then, I would say, you have a problem.
Based on what I think you were trying to say, I would think that the computer is acting to limit stress on the engine. I am basing this on the age of your truck, and a guess about a pre-programmed break-in program I seem to recall reading about here (although, it is just a guess). It could also be your injection pump isn't able to keep up until your engine hits higher RPM (again, just a guess). Let us know more about smoke, idle, behavior, oil consumption (and smell). There could be more to this. Keep an eye on it after you do your first oil change and see what happens.

(editorial note-the above description should not be used as an indication that RealBigTruck is an idiot of any kind and was not meant to belittle him in any way, just an explaination for future reference for those that didn't know)

RealBigTruck

04-30-2002, 11:32

Amianthus,

Thanks for your post. Yes, I realize that boost is not a function of rpm. I guess what I didn't make clear is that at 2000rpm with the diesel pedal floored, going up a 6% grade towing an 8k# 24ft enclosed trailer at 60mph in 6th gear, I'm only getting 13.5psi.

This seems strange to me, since I would think that with a large load (and 2/3 of the way to redline, I should see maximum wastegate regulated boost. It almost feels like the turbo is too big for the application if I can only generate max boost in the last 600rpm of the rev range with a big load.

I haven't noticed any smoke. Idle behavior seems normal (but I think I have a slight tick). I'll check oil consumption later today. What should I be smelling for?

Thanks!

[ 04-30-2002: Message edited by: RealBigTruck ]

Amianthus

04-30-2002, 12:21

What you should be smelling for is Diesel. Hopefully you won't find it.

I kinda figured that was what you were getting at. The reason I went on like that is that most people assume that the turbo spins because you are forcing air through it like a pin wheel or windmill. That's not really the case. I thought you might've know that, but just wanted to elaborate. Nothing personal, you see.

I would lean towards your injection pump being weak (provided there is no computer intervention) or a weak injector. Something that would cause a lack of fuel delivery to your engine (regulator perhaps). You may also have a bad map sensor too. Although, you should get a code if this were the case. I am also assuming that your indications are correct, and that the truck is suffering from what you would consider a lack of power. Your mileage would also reflect the lack of power problem. Other than that, do you have another Dmax to compare it to? That might give you a better idea on how it is supposed to behave. Let us know how things are coming along.

mdrag

04-30-2002, 12:24

The Dmax is my first diesel, so therefore my first turbo diesel. I own and heavily modified a '89 Supra Turbo, including a MUCH large turbo/intercooler/exhaust/fuel injectors etc.

I do not know if there is a substantial difference in the design principles of a diesel vs. gasser turbo.

I believe that a turbo gasser's boost is a function of BOTH the engine RPM (more exhaust volume/velocity) AND EGT's. The turbine speed and hence boost level is affected by both of these parameters.

This would seem to be contradictory to the information posted by Amianthus, so I respectfully disagree with his assertion that heat is the only factor involved in making boost.

If the diesel turbo setup is completely different than a gasser and operates under different principles, than I would like to know where I can do some more research on this subject and learn more.

gun runner

04-30-2002, 13:44

Mdrag, I'm with you. My limited use has always needed rpm.

Realbigtruck- I've got a 3500 cc 6-sp that doesn't run fast. I think you've found the problem. No boost , no power. Now I have to figure out how to make the Dealer fix the boost problem!

RealBigTruck

04-30-2002, 15:44

Before I can go to the dealer I need some evidence that something is wrong with my truck.

Can someone provide information about their truck? What is the lowest RPM to achieve full boost with a heavy load at full throttle and what is that peak boost pressure?

Thanks very much!

mackin

04-30-2002, 16:26

RealBigTruck,

No load no BOOST I can verify that....Went out in driveway in park...revved it to 2500 RPM..NO BOOST........Not sure you want my BOOST readings.........On the "JUICE" with wastegate disconnected.......Nice beefy acceleration 2800+ RPM, hill or no hill, on the interstate, I'll see 28 PSI empty...... :D :D Off course I wouldn't accelerate like a MAD MAN with a load........Cruising around town 30-35 speed limit 5 psi/0 psi boost...........All depends on your foot...........All the real boost readings are about LOAD ........IMHO........You can have it in cruise as you approach a hill you can just see the BOOST come up slightly, along with EGT'S not much change in RPM..........I think the lowest you will begin to see BOOST, while accelerating is when it reaches 1800 RPM pretty sure......I'll double check tomorrow.......My peak, hold on to your HAT, seen a 30 PSI ouch....LOVING IT......... :D :D I think stock max. BOOST is 22 PSI ? Someone will correct me..........
MAC
My truck is an "ANIMAL" HOPPED UP ON "JUICE"

[ 04-30-2002: Message edited by: mackin ]

mackin

04-30-2002, 16:27

Crap, I did it again...DAM...SORRY :rolleyes: :rolleyes: tongue.gif

[ 04-30-2002: Message edited by: mackin ]

mackin

04-30-2002, 16:29

I double clutched sorry................ :D ;) ;) tongue.gif :cool:
Well read this if you want---->http://www.howstuffworks.com/turbo.htm

[ 04-30-2002: Message edited by: mackin ]

Desert Diesel

04-30-2002, 16:32

mackin,

Just an observation...

It would seem at times, as though you may have a majority ownership of stock in the Edge Juice :rolleyes:

mackin

04-30-2002, 16:35

Desert Diesel,

Wish I did ,,,,,which stock exchange? Are they public? I'll take 100 share's ...LOL tongue.gif
MAC :D :D

RealBigTruck

04-30-2002, 17:00

Okay, let's try this. Can someone give me an idea of what boost they are seeing at wide open up a hill with a load at 2000rpm?

It's got to be numbers under the conditions above or it doesn't really apply.

Thanks!

Kennedy

04-30-2002, 17:02

The key here is airflow. It's kinda tricky, but the MAF sensor signal directly affects the fuel delivery. If you do not move more air, you will not deliver more fuel, and therefore will not make more power/heat and boost. The ECM basically rules here.

Turbine sizing also comes into play in that the OE turbo is sized to run very strongly right to the top, rather than hit peak efficiency somewhere in the middle, and back things up at the upper rpms.

RealBigTruck

04-30-2002, 17:35

John,

So, are you telling me that the pressure I'm seeing is normal? Or are you theorizing? I'm not sure which you mean.

I agree that a smaller turbo that allows earlier spool-up would become a restriction at top rpm. But I also think it should be possible to have a turbo that produces full boost before 600rpm before redline that is not excessively restrictive at the top end.

Someone must know what the numbers are, right? This shouldn't be very difficult.

I never had this issue with my 94 IDI turbodiesel or my WRX racecar. I never needed to be that high up in the rev range to achieve full boost.

Also, how can the motor provide max torque prior to max boost? Max torque in this motor is supposed to occur at 1,800rpm. I would think that under load at full throttle the boost should be wastegate regulated at peak torque.

Colorado Kid

04-30-2002, 17:53

Nobody with an Allison is going to be able to tell you anything about full throttle and 2000 RPM, cause it will turn faster than that standing still with the pedal on the floor. I can't help because I don't have guages.

How can it achieve max torque without max boost, easily, if torque is limited by the fuel curve rather than the airflow. The steep climb and wide flat curve suggest that the Duramax is not air limited, at least above 1800 RPM. The reason our (stock) trucks do not smoke is that, using the Mass Air Flow sensor (MAF) fuel is limited to non-smoking quantities...fuel and air increase together to a point right about peak torque, where air continues to increase, but fuel is trimmed to achieve desired (limited) torque. This is why there is so much power, and especially torque, availible simply by adding a "box" that adds more fuel, to take advantage of the available air.

Amianthus

04-30-2002, 20:48

mdrag, if you were to look inside a turbine, you will see that the blading is not a fixed pitch. It is a variable pitched turbine wheel. It starts out narrow where the exhaust enters the blades and opens up as it gets to the turbine outlet. What this does is it allows the expansion of the gasses passing through the turbine to cool. That is the heat energy that is used. It works the same way as a jet turbine works. The same as a steam turbine, gas turbine etc. Except that the pressure drop across those turbines are handled over several stages to increase efficiency.
Now, yes, the turbine will spin from air just flowing over it. But that is not where boost is primarily generated.
Try this. Drive your truck up to the top of a hill and let it coast down. How much boost does it make? Not much. But your RPM is considerable. Now using your argument, it would be because you have the throttle closed. If you find a throttle on your Dmax, I'll buy you a new truck every year for life (if my wife okay's it). The reason you have no boost is because you are not adding fuel.
If you go up the hill, you will have plenty of boost because you are adding fuel.
This also coincides with kennedy's observation that load is what makes boost. With more load (going uphill, towing a trailer, etc.), you need to add more fuel.
This was more evident by the guys who have added fueling boxes and are now getting 30 psi boost. They can't make any more RPM than before, but they have added more fuel. Hense more heat, more boost. Does this make sense?
One thing I forgot to add. Gasser turbine, diesel turbine, steam turbine, etc. are all based on the same physics. So they work the same (basically).
Also, in a gasser application, you have a throttle plate along with fueling so that can confuse things a little bit. But they still work the same.

[ 04-30-2002: Message edited by: Amianthus ]

mdrag

04-30-2002, 21:38

Amianthus,

Thanks for the additional explanation.

Here is a link I found to a great explanation of turbochargers and how they work. It contains a fairly detailed description of turbocharger operation, with enough technical descriptions to put most of us to sleep:

http://www.turboclub.com/aturbo.htm

Amianthus

04-30-2002, 22:05

mdrag, Dennis Grant put into words what I could not. Excellent article. Thanks for the research to find a better explaination.
Too bad he didn't address the operation of a VGT. Now that's mind-blowing!

imported_

04-30-2002, 23:46

vnt...variable nozzle turbocharger...allied signal (A.K.A GARRETT)good reading there

vgt...variable geometry turbo... borgwarner or KKK or borgwarner 3k .. not near the site of allied signal but ok nonetheless

TURBOLADER......VNT....VGT....same $h_t different pile.....hmmm good though ... lower axial inertia
and a kennedy 4" exhaust....edge juice box....can we say SCHWING!!!!!!!!! AAAAAAAAAHHHH I WANT ONE!!!of each..thank you for listening to this dementia.

imported_

04-30-2002, 23:54

BTW...as corky bell wrote ..a turbo does NOT need does NOT require backpressure to operate... the bigger the exhaust the faster the high pressure (due to the high enthalpy of burning fuel) HOT exhaust gasses will move from the small exducer outlet to the larger exhaust (low pressure) outlet
this will cause the turbo to spool at a much faster rate. of course there is a limit to the size of the exducer opening and of course the requisite damage from compressor overspeed (out of map efficiency range) but that is handled by a mechanical wastegate. in closing; with a vnt turbo we could all run a turbo that is 1.5 times larger than our engine does now with greater performance..less lag ... and no danger of overspeed or wastegate failure....wanna know the downside?..... ***COST***

hoot

05-01-2002, 07:23

Amianthus,

If I put a blow torch to my turbocharger and heated it to 1200 degrees, will it start spinning? I don't think so. Yes, heat is what generates expansion and air movement through the turbocharger so although what you are saying is true, the bottom line is moving air molecules are what pushes the turbine blades. Heat in the exhaust stream immediately coming out of the heads is rapidly expanding causing a rush of "wind" from the ports out of the cylinders. That is why load generates spool-up. Yes it's the heat, but it's the expansion (causing air molecules to "push" the turbine) that causes rapid air movement to the point of least resistance being the end of the exhaust system. Simply heating up the turbo won't spin the turbine.

I'm not disagreeing because I know what you are saying is correct, it's just confusing to think just heat makes the thing spin.

The turbine works alot like an air conditioner expansion valve. Allowing the refrigerant to go from a liquid to a gas through a small orifice to a larger space, the resultant gas is cold because it's the same number of molecules in a larger space. Just like if you blow compressed air through an air nozzle. The air is compressed and warm going in but gets cold on the way out because of the expansion. Expansion is the "work" created but it is in the form of moving molecules pushing against a surface.

I know I'm bouncing around here but all I'm saying is the expansion is what causes the "movement of air" that pushes the impeller blades and the larger spaces at the ends of the impeller is what allows the expansion/cooling.

From mdrag's link....

"As it passes through the diffuser and into the turbine housing, it moves from a small space into a large one. Accordingly, it expands, cools, slows down, and dumps all that energy - into the turbine that we've so cleverly positioned in tho housing so that as the gas expands, it pushes against the turbine blades, causing it to rotate. Presto! We've just recovered some energy from the heat of the exhaust, that otherwise would have been lost."

[ 05-01-2002: Message edited by: hoot ]

imported_

05-01-2002, 07:44

hot gasses have more kinetic energy than cold gasses

Kennedy

05-01-2002, 07:49

RBT,

I haven't watched things super close on the T2, but will say this. The fuel curves are driven by APP (accelerator pedal position) and MAF (mass air flow) to maintain emissions.

Basically, the ECM will only allow so much fuel delivery based on thge MAF signal, so if that amount is insuficient to create more power/acceleration, it will not continue to add fuel.

Also consider this: 2,000 rpm is basically 33% lower than peak HP RPM. Naturally, HP will be substantially lower so less exhaust energy is being produced (notice how nicely I skated around the heat/airflow debate) and since the turbine is designed to run freely to peak, you just dont have enough speed to produce the wind at this point.

Open the exhaust/air cleaner, and you move more air, and flow more efficiently, getting you more fuel earlier. Now add a power box, and this peak begins to come on earlier yet as more fuel than the ECM sees is being delivered.

On my 17k tow, I seldom passed 50% APP. In the lower gears at lower wind loads, the truck would walk right away, fan clutch engaged, until 45ish mph where the wind load took over. Going beyond 50% APP madelittle/no difference as the airflow did not increase sufficiently to get more fuel. In short, she was whipped. If I were to wind to redline prior to shifting, then it would have possibly been over the hump, but I knew that I had a tremendous wind load, and that at 52-57 mph it was most comfortable. Once I learned how to coax it into OD, I found max EGT occurred at below 1800rpm as the engine RPM was dropping, and I was maintaining as much APP as I could without causing a downshift which occurred at 1600 RPM without fail. Peak EGT was 988 on a 60

hoot

05-01-2002, 08:22

JK,

I do notice EGT's going up under load as I go into fourth and fifth gear. That's where they are the highest, under a lugging load. Nothing new here but yes, more air flow as in HP aircleaner and larger exhaust should help.

Amianthus

05-01-2002, 09:04

hoot, if you stick your torch into the inlet of your turbo charger, it WILL start to spin. Just not really quickly because the volume of the expanding gasses won't be enough for any appreciable use. (I know we are talking the same thing here.)

How do the gasses expand? By heat of course. And how do you get heat, by adding fuel.

Here's a neat example of a guy who's taken this to task.

http://www.asciimation.co.nz/beer/

It all boils down to gas laws. They are all the same. There is no way around it.
The point I was trying to make was that turbos spin independently of engine RPM. There is no correlation between the two. Heat is what makes it spin (by causing expansion of the gasses passing through the turbine). And the only way to make a turbo spin faster (make more boost) is to make the gasses expand more. And to make the gasses expand more, you need heat (fuel).

Now, since we've gotten way off topic. RealBigTruck, have there been any new developments? Does the MPG still suck? How's the performance? I'm still leaning towards a faulty fuel pressure regulator or a bad injection pump. I would assume that you should be able to apply full fueling at any RPM (based on what the computer would allow for the given boost level). SO I would think your truck is not able to deliver the fuel your foot is asking for. Just my guess.

hoot

05-01-2002, 09:35

Amianthus,

Yes we are on the same page. Guess I had some learning to do myself.

Bad fuel mileage could be related to quality of fuel.

Could have a leaky injector that's not bad enough to be obvious.

Lead foot does a job on fuel mileage too.

These trucks need good break in before mileage creeps up from what I've been reading. Maybe breakin is all that's needed.

[ 05-01-2002: Message edited by: hoot ]

Kennedy

05-01-2002, 09:57

My trip mileage sucked (16 empty @ 72-75mph) and 6ish loaded. I kinda suspected the pump failing scenario myself, BUT, if I run empty 1/4 mile, I get 16.8 seconds, and flipping on the VA (TS programming) I drop that to 15.2. The pump is obviously working...

What I have found is that at 70mph in cruise if I step it down, even with the VA box on, it accelerates just fair, as this box folows the stock fuel curve. With the reflashed ECM (pulse width) the curve is reshaped, and the truck becomes VERY assertive staying in OD.

In other words, the pressure type mods likes RPMs and the pulse width type likes to grunt.

RealBigTruck

05-01-2002, 10:26

Amianthus,

I'm thinking it's not a fuel problem, unless it's one that is RPM dependant. On the flats the truck would pull the same 8k# load over 80mph with no problem. Not that I tow that fast, but I wanted to see if it would pull harder as boost increased at higher rpm under load increased. It pulled fine.

When this truck is at full boost, it pulls great! If I'm traveling at 70 in 6th and hit a good incline, the truck slows down and boost decreases as rpm decreases, even though I've got the go pedal floored. Once it gets down to 60mph, I'll shift into 5th. RPM's go way up, boost goes way up, and oh, look, I can accelerate up this same hill up to 70mph. Of course, it's around 3000rpm!

I understand the basics of turbochargers. I'm just curious if the low boost at 2000 rpm under heavy load is a function of the computer opening up the wastegate to regulate power at lower rpms for longevity, or if it's the inherent functioning of a system that is designed for peak flow at peak rpm and low rpm boost suffers, or if this thing is just not working right.

Don't get me wrong, the power is great in this truck when on full boost. I just wish I had full boost a bit lower in the rev range so I didn't have the thrash this motor to get it to go.

Gary

hoot

05-01-2002, 10:46

I believe this motor is designed to do as you stated, RealBig. If you lug it with a lot of boost, I'm afraid the EGT's might be unacceptable. I think in 2004 when they go with the variable geometry turbo, they may give it a little more on the grunt side because they'll have some more control.

Kennedy

05-01-2002, 10:54

THE key, as stated in the intro of a form mail many of you have seen is AIRFLOW. If you can get the air flowing in/out freely, the ECM will fuel, and you will make power and boost...

hoot

05-01-2002, 11:08

So then let's talk about what to do about airflow. Are we restricted by the turbo? After all some have 4" exhaust and have not seen any incredible gains because of it. Many of us are also using the Amsoil hi-flow 2-stage air filter and have swiss cheesed the intake box. Also no significant changes. I have the air filter, swiss cheese, but stock exhaust. Running propane I see up to 25 psi post intercooler. I also see 1200+ egt's under real heavy throttle.

BIGGER TURBO HUH?

I also noticed the exhaust manifolds seem pretty puny. Not much in the way of flow there. The heads are pretty busy and as someone stated in another thread, the valves are about the size of a quarter. What am I getting at? There may be some designed in restrictions that might be difficult to contend with.

JK, we're watching your experiments closely. ;)

imported_

05-01-2002, 12:00

Hoot imho the turbo is the largest restriction that we have. this turbo is designed for appx 78% efficiency at 24-26 psi at...hmmm i have to go and find that link at home to show you..i cannot remember the exact cfm. suffice to say that a larger compressor housing on both sides of the equation would result in both higher boost pressure and volume (and less heat in the charge air pre intercooler) and thus more power. But now lets talk about how much fuel we can get out of this injection system. without increasing the fueling there will be no power increase ...these must go hand in hand. changing exhaust manifolds will not help us at this point even with a larger turbo....but there is still the issue of fuel... and with a larger turbo....MORE TURBO LAG...which is the whole reason behind VNT or VGT turbos; this larger compressor can operate in its 'powerband' (given efficiency vs.rotational speed vs axial inertia) by using vanes to enhance the angle of attack of the exhaust gasses on the exducer impeller.

SoMnDMAX

05-01-2002, 12:33

Hoot, if we went to a bigger turbo, when all else remains the same, there would be more "turbo lag", which is definitely undesirable. For us to utilize a larger turbo, or even the one we have now, the fuel curve needs to be much much more agressive!! I personally think the turbo is the proper size, if not too big for a BONE STOCK TRUCK. Once all of the high HP mods start coming out, we will need to increase turbo size, just as the D/C boys do with their Holsets. Amianthus can explain more about the Holset I'm sure.

Increasing the size of the manifolds wouldn't help us out much either, at least not until some of our trucks start making some BIG horsepower. By BIG I'm taking 450-500+ HP. At those power levels, the manifolds probably still wouldn't need much improvement (except for the drivers side). The manifolds are built and sized with velocity in mind. If you would see one off the truck, you'd know what I'm talking about. Velocity and retention of heat energy is the key to making a turbocharger work properly. No heat, no velocity, no boost....

Much of the EGT issues can be traced back to the stock fuel curve. Advancing the timing of the fuel shot will reduce EGT's. IIRC, one of the tuners on here stated one time that the Dmaxs' injection timing was quite retarded, hence the tendency to run a higher EGT. Also, propane can contribute to higher EGT's as well, more so that a fueling box would. I would be very interested in seeing some EGT examples from an Edge Juice or TTS reflashed ECM, to see exactly how the Dmax reacts to a change in injection pulse width.....

My opinion.

tongue.gif tongue.gif Flame On... tongue.gif tongue.gif

imported_

05-01-2002, 12:48

ours is the twin scroll turbo
here is the efficiency link.
http://www.ihi-turbo.com/turbo_chart.htm

imported_

05-01-2002, 12:56

turbo wish list...follow the link
http://www.egarrett.com/products/gt_30_45***p

Texasoilman44

05-01-2002, 15:06

Hello all,

I read the turbo article someone posted on here, and it all falls into line with my observations of the turbines that use here in the refinery. All of the ones we use, are a driver for either a pump or a compressor. Some of the ones that are drivers for compressors, work in the exact same principal as the ones in our truck. On a "Cat Cracker" unit, the compressor pushes air into the regenerator. This air is used for combustion to regenerate the catalyst in the regenerator. The flue gas off of the regenerator is then routed to the inlet of the turbine driver on the same compressor that pushes the air into the regenerator. Just like the article states, there is a tremendous amount of heat 1300+ degrees fahrenheit upstream of the driver. Downstream of the driver, the temperature is lower by several hundred degrees. Also, there is a considerable pressure drop across the turbine. 13 psig down to around 9 or 10 psig. So my experience with these big machines would tend to indicate that temperature and pressure are the main functions that affect the efficiency of these guys. Maybe this helps, I don't know, but the article that was posted made perfect sense to me. However working around this stuff all the time may also contribute to my understanding.

Kind regards,

Kevin

Kennedy

05-01-2002, 16:45

Well, I will not have it on for the Rendezvous, but with any luck I'll have the turbo back to display. They left some easy airflow on the table with the compressor wheel...

FWIW, I was just out with a very small 2k load, and could hit 20-23 psi boost in the 1800-2200 RPM range. This WAS with extra fueling... I could not test stock, as I had the reflash in.

Amianthus

05-02-2002, 10:32

RealBigTruck, your problem has me perplexed. Although, I'm one of those "gotta see it" people, so that may be why I'm confused.

I will say this. I don't think it's your wastegate. The reason I say this is because they are usually mechanical devices and are set to operate at one point and one point only (I know they gradually open, but they are set to open at around 20 psi and open more to maintain that set boost pressure). So I don't think the wastegate has anything to do with it.

The way you describe it, it sounds like you're lugging it. I don't know why your truck would do that with that low of a load. Something in the ECM is forcing it to defuel. Perhaps it does have something to do with break-in programming, if there is such a thing. Or lastly (and don't take this badly), the truck isn't able to handle that much load at that engine RPM (torque vs. HP). Although, that wouldn't explain the lack of boost (unless the ECM is programmed to defuel to keep EGT's in check, that doesn't make sense to me).

Anyone else have some ideas for this?

Kennedy

05-02-2002, 11:41

For a stock truck, I believe it is right where it is supposed to be.

gun runner

05-02-2002, 11:42

realbigtruck- I keep watching this forum, hoping someone reveals a good condition or reason to inform the dealer , how to fix our underpowered new trucks. One thing that seems to be happening,all 3500 6-sp appear to be slow.

anyone disagree?

MaxRock

05-02-2002, 13:49

I have a 2500HD DMax/6 speed and when I'm running it hard, I can bark the tires in 5 of the 6 gears...and yes I have the G80 locker.

When climbing a hill, the RPMs are steady but as the load on the engine increases, you can hear the turbo whine getting louder. Analysing how my truck operates in a load/no load situation, I believe the turbo's output is a function of both RPM and load, with load being the major contributor.

RealBigTruck, I hope someone/something helps you to remedy your problem.

MaxRock

RealBigTruck

05-02-2002, 18:37

MaxRock,

Do you have anything you can tow and a steep hill to see if you are getting the same psi that I am at 2000rpm with pedal to the floor?

Thanks,

Gary

MaxRock

05-03-2002, 13:26

RealBigTruck,

I do not have anything heavier than around a 6k pound load and when I say hills I'm referring to North Texas hills, not streets of San Fransisco hills. Unfortunately I do not have gauges...yet, so I really can't give you an exact boost measurement.

But what I can tell you is what I have experienced. On my way home I climb a couple of relatively tall (North Texas tall) hills. The engine RPMs (around 1900 to 2000) are constant, but the turbo whine gets louder as the load (climbing up the hill) increases. I also notice when I'm accelerate hard and shifting thru the gears the truck really pulls hard from around 1300 on up. Below 1300, there isn't much punch. Once the turbo starts whinning, the truck really pulls.

MaxRock

RWHP

05-03-2002, 19:25

RealbigTruck,

I am amazed how every answer to your post has completly avoided giving you one. Lets see if I can help you, without going into needing aftermarket products. ;)

The boost pressure on this truck is computer controled, from what I understand the fuel gets regulated to ensure that the boost proper. There have been several posts on this in the past and the results are same as yours.

Boost builds with RPM, I dont remember the exact link to this but the boost did not reach max of 18 until 3200rpm. 18 you ask? But I am seeing 20? Well that is because you are reading at turbo rather than inlet manifold. At the manifold you will loose 2 psi to pressure drop.

Hope this helps.