Ronniejoe any input?

[7.4 VORTEC]

Good Day,

Getting ready to bump up the power a little in a 1999 Hummer with a 6.5TD. At this point, I want to run without a intercooler because it's a major undertaking with a Hummer.
I followed Ronniejoes build up and am very impressed with the overall outcome. Here is where my boost question comes into play. Most GM trucks on the board with overdrives probably run anywhere from 1800 to 2200 rpm at 65 mph. In overdrive, my Hummer is at 2500 rpm at 65 mph (thats with 37" tires!!) The gear reduction hubs really drop the gearing down. What kind of boost should I be aiming for at these higher rpm's when cruising down the hiway?? Since I'm running such high rpm's, it just doesn't feel like a "normal" turbo'd truck that boost's up when under load. I understand that the torque peak of the 6.5TD is around 1800 to 1900 rpm, but I'm almost never in that low ballpark unless cruising on city streets. If I keep up with highway traffic, 2700 to 2800 rpm is the norm. I'm just a little concerned that a computer upgrade designed for a truck or suburban may not be right for my constant higher rpm's. Also, my truck weighs approx 7800 lbs.

If anyone else has any experience with this, I'd appreciate any input.

Thanks,
George

[7.4 VORTEC]

Anyone have any ideas regarding cruise boost at high continuous rpm's??

Thanks,
George

[Hubert]

I think you are comparable to a loaded 1 ton service truck running 4:10 gearing or is it 4:11 ? Maybe just a few 100 rpm higher. So its not such a different animal. A reputable program upgrade should work a OK.

I don't know about boost cruise 4 lbs maybe with that weight depends on how much fuel is required to cruise????

[Mark Rinker]

Sounds like a fun project. Here are my thoughts - which tend to be more based on personal experiences, rather than hard science. Hopefully, RJ can chime in with the thermodynamics/science part.

Your gearing and RPM numbers are very similar to my #1 and #2 plow trucks listed below with much smaller rubber. #2 has a Heath chip and Turbo Master. I have experimented with many different settings on both and monitored EGTs, fuel consumption and oil consumption (blow-by).

Boost is a point in time measurement of a very dynamic set of factors in the 6.5 TD. There is no 'optimal setting' for all conditions. There probably is an 'optimal average', but this still requires that you monitor things like EGT in relation to your chosen setting.

My thought, based on your application, is that a nominal setting of 6 to 8lbs when cruising on level ground at 65mph with no intercooler would be safe. You will get some EGT cooling effect at or near your optimal boost setting from the additional airflow. Tuning by EGTs is a good way to go, but there is certainly a diminishing point of return without an intercooler present. More is not always better IMHO, especially if you are not intercooled.

In short, the LOWEST nominal boost setting to produce the LOWEST nominal EGTs at cruise is your goal. With boost settings above that, your air charge temps will start to increase sharply without an intercooler - and most of us aren't monitoring that data. Add to that a hot day towing in the mountains - and things can get ugly quick.

All of this is dependent on a myriad of factors including outside air temperatures, altitude (air density), etc. Your engine needs to be breathing easy (intake and exhaust) before its chipped. Then adjust your boost to match those mods.

[moondoggie]

[font=times]Good Day!

[i]

[john8662]

I think RJ's on vacation...

[7.4 VORTEC]

Thanks for the info guys. The injection pump is controlled electronically, just like all the 97+ GM trucks. I do think that tuning by boost and pyro would be the way to go. It's just tough to explain the "feeling" of the truck. It has a ton of frictional and aerodynamic losses. If cruising at 65 in overdrive and if you instantly let off the fuel, the truck slows down as if you were to drop a normal Chevy pickup from overdrive to drive then to second. It's always full time 4wd, big tires, gear reduction hubs and the aerodymanics of a billlboard:)
When rotating the tires, I get winded just pushing them around front to rear, those suckers are heavy and hard to roll.

The exhaust isn't too hard to open up. The intake is another matter. The snorkel breather is in a good position (high pressure area), but makes very tight and numerous bends into the air cleaner canister and finally to the intake side. I do understand that this is a military based vehicle and a huge compromise to drive on the street, but the challenge of making it work better is part of the appeal to me. I'm just hoping some of the experts here on the board take interest and maybe we can all learn what works.

I'm just trying to learn what the relationship of high rpm vs boost should be in "correct diesel theory". Since a reprogramed pcm is sort of a "done deal", I'd like to know what boosts to request at a given rpm before I jump into one blindfolded. Look forward to hearing from you all. Should be interesting to hear what Ronniejoe thinks when he gets back.

Thanks,
George

[DA BIG ONE]

I'd consider getting the highway hubs for that H-1 to bring down those rpm's, I don't even know where to look for em, but I have read many times that they are available.

I would also consider the heat problem the H-1 has because of it's drivetrain tunnel design, the t-case has it's own cooler (prone to failures) for this reason. Cooling upgrades to the tranny, t-case and differential should be considered a must when going for more power on the H-1.

Perhaps, larger diameter tires are a good idea.

[JohnC]

There is no direct relationship between boost and RPM. Boost should be related to fuel rate. The more fuel you want to burn,the more air you need to burn it. Since you cruise at a higher RPM, the load is less than it would be if at the same road speed but a lower RPM. Basically you are moving the same amount of air and fuel through the engine but doing it in more, smaller "bites", hence lower boost.

I'm sure this doesn't answer your question...

[twaddle]

George (7.4 Vortec)
I think your main problem is the low gearing which is giving you the high revs at cruising speeds.
Is there any spare space between the transmission and the frame to install an overdrive. That would be of more benifit to you if you want the cruising revs to come down a bit.

Regards

Jim Twaddle
Biggar, Scotland

[7.4 VORTEC]

Good Afternoon Guys,

Da Big One - Let me know if you have any source regarding different hubs. AMG went to a lower numerical ring & pinion to drop the rpm's down and my year Hummer already had that. I've thought about having different planetaries made for the hubs, but then you're locked into that gearing for good.

John C - Your comment is exactly what I'm trying to find out. I listed this to RonnieJoe because I thought he talked about this relationship, I just can't find the thread yet. I know under low load, high rpm conditions, there has to be some thought as to what boost you would run (either lower or higher).
I'm figuring it will be strictly based on a boost gauge, egt gauge and maybe a dial as you drive boost controller to find what is optimal. An intercooler would be nice, it is just a major pain on a Hummer. (new fan shroud, possible body lift, etc) Also, I can't run any type of "free wheeling" hub at the wheel, I'd lose my front brakes because the rotors are inward against the diff.

Twaddle - I have researched doing a Gear Vendors overdrive, they don't make one for my transfer case (242) and suggested I change the transfer case to a unit they already have adapters for. (Gear Vendors + new transfer case...yikes!!) The Gear Vendors would be the perfect solution because I've already sourced a front drive shaft quick disconnect so I can run in rear wheel drive only. The transfer case just gets shifted to Hi Lock and you leave it there.

I think your side of the pond has an overdrive from a company called GKN (I think). I'm also told that the Gear Vendors in the USA are made by a UK company, so I wouldn't be surprised if it was them.

Regarding bigger tires, I'd need 40" units to be in a "normal" rpm range. I'd also need a body lift to clear them. The bigger tires will also kill performace, even with corrected gearing. Those suckers are heavy and would take even more energy to keep rolling. I have seen some Hummers with them though and from a looks factor, it's awesome.

Lastly, a new Allison 6 speed transmission would be pretty cool, I don't know if it would fit without some dimensions. A unit out of a wrecked truck would be great, assuming you can get the computers to "talk" to each other.

Thanks for all the input.

George

[DA BIG ONE]

40" tires will work ok w/diesel & performance upgrades because the torque will be much higher than stock. The H-1 does use more energy to operate becaue of its flat frontial surface.

See my signature of what things I have done to my burb's motor. Only issue I have is tranny shift points under 45mph, and there are no fixes because I have the NP 246 AutoTrac which uses 3 speed sensors, along w/ABS to operate. When I shift manually there are no issues!

I'll see about getting hub info for ya.

[ronniejoe]

Sorry to be so late in responding...

On the electronically controlled engines, boost is tied to rpm through the computer. Above about 2500 rpm, the computer cuts back on the wastegate solenoid duty cycle allowing the waste gate to modulate boost pressure. The higher in rpm you go above 2500, the lower the duty cycle percent falls. The end result is low or no boost at high engine speeds.

When my Suburban was stock, my boost gage read zero at 80 mph... This equated to about 2900-3000 rpm. By adding a boost control to the BARO sensor, I fooled the pcm into maintaining a higher wastegate solenoid duty cycle and was able to bring up the boost here. Now with all the modifications I've done, I cruise at around 10-12 psi at 80 mph, depending on road conditions. The egt is about 400 degrees cooler now than when stock.

If you can stand to alter the gearing, I'd say that would be a good idea. However, just ensure that you correct the vssb to get the speed sensor right. Also, I would look to increase boost as much as possible to lower egt at the high engine speeds that you must encounter. Gages are critical. I would also highly recommend some form of charge air cooling.

Good luck!

[7.4 VORTEC]

Thanks Ronniejoe,

I'm trying real hard to get a manufacturer to work with me on an overdrive. That would solve a lot of problems. I'll have some more answers this upcoming week to the overdrive situation.

Did you make your own "boost fooler" or is there a commercially available unit?


Thanks,
George

[moondoggie]

Good Day!

"Above about 2500 rpm, the computer cuts back on the wastegate solenoid duty cycle allowing the waste gate to modulate boost pressure." Not to argue, but only to (maybe) clarify: I remember reading quite some time ago in one of the topics that this actually begins to occur at ~ 1800 rpm. This was mentioned by someone of great knowledge, like RJ.

I know that, with my Gear Vendors Aux. OD, I've seen ~ 10 PSI boost at 70 mph, but I'm only turning ~ 1750 rpm @ 70 mph, so whether the PCM starts looking at boost at 1800 or 2500 rpm, I'm in fat city at 70 mph. If I can manage to remember to do it, I'll put it at 60 mph without the GV engaged, which would give me ~ 2000 rpm, & see if the PCM attenuates boost or not.

JK, among others, makes a boost fooler. I think it's probably a pretty simple circuit, just never yet had time (or need) to make my own.

Blessings!

(signature in previous post)

[ronniejoe]

Used Kennedy's.