Theoretically speaking...

[Spindrift]

...if you were able to significantly reduce IAT on a 6.5TD that hasn't been modded by a performance chip, would it be possible to reach boost levels in the 12-14 psi range? Or, is fuel delivery always going to be a limiting factor?

[gmctd]

20psi max with a GM-8, no charge-air cooler, during Winter R&D - IAT climbs rapidly.

You can run 12-14psi all day long, GM oem chip, mechanical boost controller, electronic boost fooler may help with Wastegate DTC's.

Fuel rate at 62-63cmm OBD-1 - your OBD-II '98 may do better.

The 'chips' deal with the DTC's, alter fuel rates and timing.

[rwpierce]

Bill Heath gave a talk at Rendevous 2 at Bigleys and stated, if I remember correctly,that 12# boost was maximum with the 21.3:1 compression that you can run.I don't remember the reasons why well enough to repete but if you e-mailed him I bet he would fill you in .

[gmctd]

High exhaust back-pressure in the GM-X series of turbos limit productive boost to 12 psi.
12psi also keeps Intake Air Temperature within operable limits where a charge-air cooler is not installed.

[Spindrift]

jd,

Sorry, I'm still a little confused. Are you saying that the truck can run at boost levels in the 12-14psi range without a chip but with the chip, in addition to fooling the computer so that it doesn't throw DTC's, it also increases power by supplementing fuel delivery and altering timing?

I was under the impression that there is a direct relationship among boost, torque, HP, and fuel delivery, or, you can't have an increase in boost without a proportional increase in fuel delivery. An oversimplification or I'm just way, way too far off base.

I apologize if I'm tapping you for a crash course in Boost Dynamics 101.

[gmctd]

I don't mind questions, long as they're not about 'where do babies come from'. ;)

Your understanding is correct - it's how much increase to which parameter that is the limitation.
And the GM-X series of turbochargers is sized small, to function in a low exhaust volume confiiguration, providing 'driveability', or - no turbo-lag.

Based on my observations -

The PCM is constantly limiting boost - at 7psi, the wastegate is bleeding off exhaust flow needed to make boost above that pressure.
Exhaust volume is there, or PCM would not need to limit vacuum to wastegate.

Step on the loud pedal, and the PCM reduces vacuum to the wastegate even more, limiting boost to around 6-7psi.

Fuel delivery is there, to 63cmm, but the PCM is limiting boost, and will cut back on fuel delivery to match boost level. You'd see lots of black smoke, if this did not occur.

Purpose is to keep Intake Air Temps within a range that doesn't reduce power.....

....for the average production line truck, with cramped exhaust, limited cooling, poor quality fuel, etc - all things that also drive EGT upward during power demand.

A mechanical wastegate controller removes PCM limitations, and can be adjusted to allow 12-15psi.

PCM sees 12-15psi, you get 63cmm fuel - stock oem chip. Your OBD-II may get more fuel than my OBD-I EFI.

Hot chips boost fuel to above 78cmm, vary timing, hide several DTC's - these require a charge-air cooler to keep IAT at near ambient to take advantage of the fueling increases.

But, then, most all of our trucks could benefit from charge-air cooling, to reclaim the power lost to hot air.

[JohnC]

Counterpoint:

The PCM has a map in it that relates throttle, RPM, boost and fuel rates. Adding boost without modifying the fuel rate will provide only minimal performance gains. Going to 12 psi is probably no better than 9 psi and may be worse due to the added backpressure associated with holding the wastegate closed longer. The PCM maintains minimal control over boost, only caring if it exceeds safe levels. Fuel on the other hand, is controlled with an iron fist. No chip change, no fuel change. the PCM is still going to reduce the fuel rate at higher RPMs regardless of whether the boost falls off as expected or not.

On a gas engine, fuel is metered according to airflow, so increasing boost increases fuel and power. On our Diesels this is not the case. Fuel is metered according to throttle setting and is only minimally related to boost pressure.

The PCM never giveth; the PCM only taketh away...

;)

[gmctd]

Excellent counterpoint, JohnC, most closely aligned with my previous thinking.

I'm still at the mine, working the salt, so hold that thought. I shall prepare and submit a paper in response, later. ;)

[patrick m.]

This is my kind of reading, in fact, i'll give the professors another situation to explain, (should you decide to accept) :D
i have four (4) turbos, ive been playing with them to see how they perform, and how they perform differently. The first is the original GM-4, came on boost very quickly, and maxed out at 15psi evenwith unregulated vacume applied to the wastegate.
The second is a Garrett with a 1.0 A/R turbine, .60 A/R comp (and lots of other specs we can get into later if we need to).
The third is a Garrett (both non-wastegated) with an .89 A/R turbine.....comp the same as the first.
The last one is a Schwitzer, about the same turbine as the second Garrett, but with a smaller compressor.

The Question is: why do all of them peak at 15-16psi, and all except the GM-4 wont "spool" up before 2000rpm
three different turbos, all come in at the same time, all sound just alike, all produce the same max psi.
Only the GM-4 has a wastegate.

I had a turbo shop tell me that any of the last 3 should easily produce 25-30 psi.

Peninsular told me i would not get that much boost with stock compression.

one of you guys can explain this i am confident. :cool:

[rjschoolcraft]

I have to disagree with the comment about max productive boost is 12# with the GM series turbos.

Mine runs up to 13.5 to 14 psi around here under load. It definitely keeps the EGT's down lower than if the boost were lower, so that is very productive. Furthermore, I think it makes the engine more efficient (lower egt would indicate that) because it reduces pumping losses in the engine (improves volumetric efficiency) thereby putting more useable power to the ground. This is not instrumented data, but it is seat of the pants feel.

When running at elevation, my Suburban will boost to 16 - 17 psi...compensating for the thinner air at altitude (thank you "BARO" sensor).

[freddys]

From what I have been told is that if you don

[gmctd]

Taking a break from my 'paper'...

Far as the turbos go, Patrick, it's a matter of required exhaust energy, in volume, heat, and velocity.

Install the .89 Garrett and wrap cross-over pipe to retain the required heat. Keep engine rpms up to get the volume and velocity.
And\or, go to a .69 turbine housing, .80 compressor to produce at lower engine rpm.

And, don't try for those over 15psi levels - the stock 6.5L cannot handle those pressures for very long.
freddys is correct about the fuel, but that should only be attempted with the 18:1 street motors.

Ronnie, the problem with the GM-X series turbo is exhaust back-pressure rises somewhat drastically above 12psi boost, much worse above 15psi, as can be observed by plumbing a pressure gage into the exhaust manifold. BD has a kit for that, IIRC, for their exhaust brake - seems like Tanker installed one on his 18:1 Sub - brake and gage.

My truck was tapped, plumbed, and gaged but had to remove it to pass state inspecion - all 'dooleys' are considered commercial in Texas, and subject to DOT spot inspection by hiway patrol.
No exhaust source allowed in the cab, 304ss tubing and fittings, not withstanding.
I was seeing in excess of 20psi ebp pre-turbine below 12psi boost, stock chip, -1.5TDC offset, GM-4, 3.5" exhaust.
Could have been that TDC offset was incorrect for the way heavy 3500, needing closer to -0.5.
But, that's what I observed.

So - still correlating pre-chip data for the previous discussion. Slowly, as I did not write it down while testing. :(

[ 04-17-2004, 09:23 AM: Message edited by: gmctd ]

[gmctd]

2). I've been using a Tech-II, attempting to answer some EFI questions, using winter temps for reduced Intake Air Temps to allow some experimentation with Boost levels

Why does Boost spike to 12, then hang at 7-8 psi, when demanding power, as from 45 to 70mph in overdrive?
Does the PCM reduce fuel for control purposes, or just for over-limit protection?
Can I get max oem fuel rate with just a boost increase, and is it useable?
What is this thing really doing, anyhow?

Wastegate Duty Cycle starts at 63%, at idle or normal driving. Under power demand, fuel rate increases, but WDC drops, both according to demand.
Heavy power demand, fuel rate increases to 62%, WDC drops to 47%, then to 40%, then to 35%, as low as 20%, trying to limit Boost to 7-8psi. Does this on long hills.
Fuel rate has dropped to 55cmm, then somewhat lower as WDC drops, but PCM does not always reduce fuel as WDC drops.
Why? Not sure yet. Temp, rpm, mph, desired vs actual advance, APP position? Fuel temp?
The Tech Menus take some time to manipulate, and opportunity is fleeting in traffic.

Also, the Menus are formatted rather inanely, as tho parameters were added as they 'popped' into someone's mind. Wish they were user formattable - vehicle speed, engine rpm, boost, wg duty cycle, IAT, ECT, fuel temp, fuel rate, injection pulse width, injection timing, TDC would be in good ordered succession.

Anybody see a need for glow plug voltage and glow plug relay status to be stuck in the middle of operating\driving parameters? Anyone??

But, I digress -
Modify Boost to max out, kick it, and Boost goes to 20psi, fuel rate goes to 63cmm and stays there until I back off, keeping an eye on IAT and EGT.
WDC still drops, tho defeated, but fuel rate does not.
If I don't back off, wastegate DTC-78 occurs in ~20 seconds.

Fuel rate never decreases at higher Boost levels prior to DTC - only when PCM is normally controlling (limiting) to 7psi.

Does appear as tho PCM can reduce fuel for other than hi IAT, hi ECT, hi Boost, etc.
Does appear as tho wastegate is always 'wasting' exhaust.
Does appear as tho a mech boost control is functional to full oem fuel rate at 12-15psi.

As per JohnC, to get more fuel, you will need a 'chip' .
And cooling, and exhaust, and charge-air cooling via mist or heat exchanger.

So, kick up the boost to 12psi, and it will perform better than 7psi, particularly if IAT can be maintained to ambient..

I had more data such as inj timing, inj pulse width, and such, but I installed Bill Heath's Max-E-Tork last week, and those oem numbers are going vague. Just shoulda wrote them down, first.
I've seen over 73cmm fuel on the one run, so far, and it was truckin' - all 8500lbs of it!
(You were right, Bill Heath - it's a good chip for my old Bud Draft Horse - thanks!)
Saw some other stuff, but I'll need some more runs before the new numbers sink in.
Hell, my palms were sweaty, it was so much fun! I wasn't reading - I was smilin' and drivin'!

And, I'm dyin' if I'm lyin'! ;)

Also verified the truck gages accuracy with the Tech

Again, 20psi is pointless with the GM-8 because exhaust back-pressure is greatly higher than boost at that level, but I was getting numbers.

So - Slings? Arrows? Outrageous fortune? Anyone.......

[ 04-19-2004, 03:29 AM: Message edited by: gmctd ]

[JohnC]

Originally posted by gmctd:
So, kick up the boost to 12psi, and it will perform better than 7psi, particularly if IAT can be maintained to ambient..I read the whole post carefully, and don't understand the basis for this statement. Are you finding the PCM holds the fuel rate higher longer if the boost is not allowed to drop down to the PCM setting?

Don't confuse wastegate duty cycle with boost. the duty cycle controls the force pulling the wastegate closed. It fights against the force pushing it open which is dynamic, as you know. But, as the exhaust flow goes up you need a lot more wastegate action just to keep boost in check.

A system with a completely open wastegate will still develope a couple pounds of boost under even moderate loads.

Years ago I did a lot of testing to get to the bottom of DTC 78. When boost excceds the PCM's idea of right, the PCM starts reducing the duty cycle in an attempt to control the manifold pressure. It'll keep reducing the duty cycle until the fault has been present for 20 or 30 seconds, at which point duty cycle drops to 0 and maximum fuel rate drops. this is to handle the case where the wastegate is stuck shut.

Up to the point where it goes into fault mode, it seems to me that it is running off the normal fuel rate curve, and is not adding fuel to match the extra boost.

Oh, I've lost my train of thought...

Set the Tech 2 to record and analyze the data later, rather than trying to mess with it at the stoplight.

[gmctd]

Correct - and syntaxal concept correction - defeat PCM control with a mechanical, or other, wastegate controller, and the advantage is 63cmm fuel with 12psi boost, compared to 63cmm with 7psi boost.

Want more fuel - ya gotta get 'chipped'.

p.s. I see what you mean, John, after re-reading it again. And again. And....
Did a little re-structuring - maybe it's not so muddy, now.

[ 04-17-2004, 05:38 PM: Message edited by: gmctd ]

[gmctd]

Spindrift - I see you have a boost controller installed.

I've been wondering why you posted?
Was it the instructions regarding springs vs PCM upgrades, or some other factor?

[ 04-18-2004, 07:08 AM: Message edited by: gmctd ]

[Spindrift]

jd,

[QUOTE] I've been wondering why you posted?
Was it the instructions regarding springs vs PCM upgrades, or some other factor?

Can't seem to get that darn quote thingy to work.

I'm trying to see how much "punch" I can get out of my current set-up before I look at investing in either an IC or mist injection, or the chip. I'm really interested in determining if the incremental value of each mod can be pushed to the limit before I go to the next stage. How much can I push the Turbo-Master? If I tighten the spring past 7psi I get the SES.

What if I ground out the MAP sensor? I think this will solve the fault code, but at what "cost"? If grounding out the MAP doesn't cause the sky to fall, then I should be able to tighten the T-M spring even more for greater boost. Right?

Just got back from a trip towing a 9,600# trailer. Saw a lot of nasty, long climbs. I was probably averaging EGT's in the 900-1100 range. Without first getting more boost, I won't be able to get those EGT's down to something a little more to my liking.

So jd...the $10,000 question is: What's my next mod? I'm just chompin' at the bit to go mist, but whether I go that route or the IC route, do I have to chip the truck first?

Oh yeah, on out trip this weekend I had the pedal to the metal quite a few times for short periods of time (until I saw 1100-1200EGT), then I would back out a little. When the pedal was floored...6-6.5 psi. When I backed off the accelerator a tad...boost would climb to 7, maybe 7.5psi and that's as high as I saw. What's up with that? Thought I would have seen the highest boost when pushing the pedal thru the floorboard.

[DmaxMaverick]

If you are trying to fool the PCM as to the MAP readings, do not ground it. You will get the SES for lack of boost (or it will think so).

Best solution to fool the PCM is to install a resistor on the sender wire, between the sender and PCM. You can do this with just about any "variable" type of sender. What happens is the signal is "buffered", meaning it is changed, up or down, in correlation with the sender's output. The selection of the resistor would depend on the range of the sender. For example, if the sender has a range of 100 ohms (ie: 180 ohms to 280 ohms), a 10 ohm resistor would have a 10% effect on the output that the PCM sees, theoretically speaking. Just find a range that both you and the PCM likes.

Another option would be to install a vairable resistor (or reostat). As long as the reostat is capable of the range you need, it's just a matter of turning a knob or screw to make adjustments.

Definately keep an eye on the EGT's. You may get the "it's not nice to fool the PCM" results.

Good luck.

[gmctd]

Grounding the map sensor will cause Boost Sensor Fault DTC's immediately you crank the engine, and will not go away.

Solution - A 10k linear potentiometer installed across the Boost sensor, between pins A-B-C, adjusted to about 1/2 rotation, will give you 10-12psi with no DTC.
John Kennedy and others sell this setup.

I soldered up the parts and wired them in, for playing.

Or, Bill Heath offers the Max-E-Tork PCM upgrade, for use in conjunction with his boost controller.
John Kennedy, BD, and others offer similar upgrades. Hides the good stuff from the PCM police - no DTC's.

I haven't tried the others, but for right now, I'm satisfied with Bill's chip, installed a week or so, ago.

I also have a 100-325deg Isspro Oil Temp gage, with modified probe installed in the intake, to keep an eye on Intake Air Temps when I'm playing.
It matches the Tech-II in response and accuracy.

Even with oem chip, it indicates some type of charge-air cooling is required when Boost levels are increased.
Observed over 700mile trip thru Texas Hill Country, even 7spi would get slightly over 200deg, and ambient was only 60-70deg. Did not burn the a\c at any time, engine coolant 180-200deg, EGT 750-1000deg, no downshift from overdrive, 2.99 effective final drive, 8500lbs + passengers and tools.

Oem fuel rate is 63mm max in my '95 OBD1 - your OBD-II should be at least equal.
Fool the Boost sensor, crank up the Boost controller to 12psi, and efficiency will increase.
More oxygen blows thru the cylinders, and quicker, at 12psi than at 7psi.
IAT can run 200deg and up even at 7psi, so cool it, or keep an eye on it.

I'm still puzzled at PCM reducing fuel rate, with temps and other parameters normal, no DTC, at 7psi boost.
According to most wags (me included), OBD-1 is not that smart, altho I see the correct parameters being monitored to allow that function.

In your case, hi IAT could be responsible.
Could also be fuel rate, as I observed.

So, try the PCM faker-outer - everyone seems to like it, and it's only a dollar two-ninety-eight if you build it.

Charge-air cooling, maybe next - recovers the energy lost to 200deg compressed air. Mist or heat exchanger - your choice. (Chill the water for mist, get 60deg charge air, lowers all the operating temps, inclusive. Block of ice, insulated tank - oh, yeah!)
Charge-air cooling paves the way to further upgrades.

All as a matter of honest opinion, of course.

[JohnC]

Originally posted by gmctd:
Correct - and syntaxal concept correction - defeat PCM control with a mechanical, or other, wastegate controller, and the advantage is 63cmm fuel with 12psi boost, compared to 63cmm with 7psi boost.OK, I think what you're really trying to say is that if you hold the boost higher while the PCM is trying to reduce it, the PCM will hold the fuel rate farther into the RPM range than it ordinarily would. This would result in a performance increase, but surprises me given the goals of the programming (Reliability and emissions).

If this is not what you're saying, then I still can't figure out where the performance increase would come from. Simply adding air without changing the fuel rate only improves performance if the engine is already over fueled, an unlikely scenario given the emmissions constraints.

[gmctd]

Correct, John. I observed that an increase in boost keeps the fuel rate up.
(How's that, for succintness?) :rolleyes:

Altering programmed limits can also alter restrictive goals, right?

Had you tried any of the suggested "improvements", prior to your JK upgrades? If so, your results would add to the knowlege base, pro or con.

I still have some puzzles that require answers.

[Turbine Doc]

I too have been collecting data via a Snap On MT2500 which does not have all the bells and whistles of the Tech 2 but has most of them, my data is pretty similar to what JD is finding, including the backpressure readings at higher boost levels.

I'm still working on the Heath PCM reflash for optimization of my hybrid L56/65 set up, some of my results differ from expected results from Bill's experience, we theorize the bottlneck is the L56 intake which will be retired for a L65 intake once my extended warranty goes away.

[Spindrift]

Given the results of the testing which has been completed by those posting on this thread, is there any hard data that would suggest lower IATs are necessary before you would gain maximum advantage of reprogrammed timing and fuel delivery?

[JohnC]

My thoughts on most "upgrades" I tried are pretty pessimistic, so I think I'll keep them to my self. Suffice it to say I ended up with what's showing in my sig. One thing I did that was very positive, before the aftermarket stuff, was change the L56 chip for the L65 chip.

Most of my experimentation has been an attempt to devine the inner workings of the PCM, which to a large extent still remains a mystery...

[Turbine Doc]

High IAT is one of those things PCM does attempt to limit by clipping boost and or fuel. PCM is blind to EGT so GM in defensive mode from what I can glean from the manual description and looking at parameters on scanner, the PCM program looks at baro, IAT, MAP (boost), WG, RPM, and (MAF in L56) and clips fuel/boost to make sure all stay on the programs algorithm(curve) for a given set of conditions.

Spend some time with Bill Heath and he can better describe what the interaction is between all of them.

Are the mods worth the buck depends what you are doing with the truck, as a daily driver probably not do the longevity stuff, if you are going to do some HD towing a resounding yes IMO.

FSD mods yes for both tow and DD, the rest more to benefit for towing improve airflow inlet/exhaust 1st, gauges after that, then boost control which will improve driveability for both.

Then as speed addiction grows or need for more power then start adding fuel, chip/reflash depending on PCM type, injectors, IC or WMI order of preference is yours, but if adding more boost maybe IC/WMI before fuel that is the way I did it.

Some other mods for longevity 97+ water pump & dual therm, early engage fan clutch, bypass dual oil filt, deep trans pan, hi cap diff cover, aux trans cooler, frame rail pre lift pump fuel filt, long dwell glow plugs, Parker replacement oil cooler lines GM prone to leak. Those sort of along how deep is your wallet mods.

Those are the easy bolt on mods, rest require going into engine.

[Spindrift]

but if adding more boost maybe IC/WMI before fuel that is the way I did it.

Now I'm confused! Isn't there a more or less direct relationship between higher boost and increased fuel rate, i.e. can't have higher boost without more fuel delivery? A chip will provide an additional 6-8 psi, and more fuel. Will lower IATs provide that same kind of "return"? That's why I'm thinking to chip first, lower IAT second. Or, did I misunderstand you? Always possible at this time of day.

[gmctd]

Spindrift, the turbocharger on your truck is sized for a 250 to 300 cubic inch engine.

Because of this, your 400 cubic inch engine will make 20psi Boost, guaranteed, with the oem program.

Your truck will return Wastegate DTC within 20 seconds at 20psi Boost, guaranteed.

Your truck, running 20psi Boost, will achieve Intake Air Temperatures approaching 300 degrees, guaranteed.

Your truck Exhaust Gas Temperatures will go thru the roof at 20psi Boost, guaranteed.

Install a Boost offset control, adjusted to around 12 - 14psi, will control the DTC.

At 12 - 14psi, you will need some type of charge-air cooling, as IAT will always be in the 200 degree range.

And, if you have not, do a 'search' here for more information on boost, intercoolers, upgrades, etc.

Some informative information on fueling and turbocharging is also on the 6.2L forum.

Do a 'search' there, also. It's about mechanical fuel injection, but the engine doesn't know what technology is feeding it. The fueling and timing improvements apply.

Should be more than enough information to help with your decision.

If not, post back.
And remember - I do better with multiple-choice questions! ;)

[ 04-20-2004, 09:47 PM: Message edited by: gmctd ]

[Turbine Doc]

Hey Spin,
go to this thread on how stuff works.com scroll thru the turbo info it's got a good bit of info including why low IAT is desired.

http://auto.howstuffworks.com/turbo5.htm

[Spindrift]

Thanks to everyone for your patience. This is fun!