OK, I have way too much black smoke. I got about 200 miles on the motor and opened her up and ran out of boost. I only got 17 psi of boost out of my T04 turbo. Uncertain of why I have low boost when I should be getting 25 psi, I put the GM-8 on and closed the waste gate.

After running the stock GM8 with a homemade turbomaster that was using a threaded rod and only nuts jammed to hold it closed, no springs to let out exhaust, I only got 11 PSI out of that turbo. I spins free, my crossover has no leaks, I don't get it, I should get 20 psi out that turbo like CR, right? What is make boost on a GM8?

I am thinking a turbo on a diesel needs to be a "diesel" turbo, or am I wrong. My Garrett is VERY large exhaust and a smaller inlet (larger than a GM8 though).

Oh yea, and running my scanner and watching my torque, I got 450 lbft with the T04 garrett @17psi and only 390 lbft with the GM8 @ 11psi.

Seeing you now have 18:1 that GM-8 is probably putting out near the same but your trying to pack it into a larger space, hense less pressure because of more volume required, just a partially educated guess though... its either that or your you turbo just aint up to snuff. Try and load it up by driving up a steep hill without it downshifting or pull a trailer and see if you get more boost, but i'd still be leary of the bottom end without splayed mains or the girdle kit.

Is your crossover pipe mandrel bent and heat taped? Have you smoothed the flow from the exhaust manifolds coming out of the heads, smooth flow coming into the turbo from the exhaust.... just a couple things i've done to get a little better flow.

without a problem i get 15-19 psi out of my GM8 and its as loose as a whore... think we should mount that t4 on mine and see what happens

Put a charge-air cooler on it, then pull a 5000lb - min - loaded trailer....................

I am gonna do the cross over pipe in mandrel bent smooth 2.5. That might help. I kinda was thinking the along the same lines as you are right now with the idea of now having more are to cram air into, which will mean less boost due to a greater pressure loss.

Like JD said, all that boost is no good if it is 250°f+...

2.5" crossover is too big, but then what do I know, mine are only 1-7/8" on the Dmax at 500+ RWHP....

Like JD said, all that boost is no good if it is 250°f+...

2.5" crossover is too big, but then what do I know, mine are only 1-7/8" on the Dmax at 500+ RWHP....
John you sound cranky:lol:

MY IAT only hit 150 C, I was just runing down the road, got the truck up to operating temp and tried to make Max boost and all I got with the GM8 was 11 psi.

Why would a smaller crossover be better? For the higher velocity that it will make?

I do have my intercooler parts on the way. I have all 3" aluminum tubing and a 24X12X4 intercooler, 3 in, 3 out. How bout that, sound OK?

Seeing you now have 18:1 that GM-8 is probably putting out near the same but your trying to pack it into a larger space, hense less pressure because of more volume required...

CR -

Unless he has increased the displacement of the engine, he is still packing in the same volume of air. The "fixed" volume of the chamber has nothing to do with displacement. That fixed volume can be considered "dead space", so I don't think that is the problem.

I am unsure of the cause, but since his compressor outlet temps are so "low", I would surmise that he needs a smaller exhaust housing. The T04 turbo has been used on 466 cubic inch farm tractors turning 3500+ RPM and can easily make 20+psi of boost.

It is hard to diagnose without being there to "see" and "hear" all of the available information. But I suspect that you need more heat energy to run the compressor (via the turbine).

Heat wrapping the x-over may also help, but probably not much.

MY IAT only hit 150 C
150 centigrade is kinda hot 302f :eek:

150 centigrade is kinda hot 302f :eek:

I assumed that was a mis-print!!! Since mine only hit 187 deg F with 10 PSI...

Yes, my bad:D . It is in F, oops.

Yes, my bad:D . It is in F, oops.
150F aint bad

150F aint bad

but it still doesn't make sense, non-intercooled, at 11 psi, unless the ambient was about 0.

killerbeeQuote:
but it still doesn't make sense, non-intercooled, at 11 psi, unless the ambient was about 0.

Killerbee:
the computer reads the boost as 26, 11+15 (atmospheric) if that is what you are talking about with the ambient pressure. But that 150 F is with low boost, when that boost increases to where I want it to be, it will be like 200 F probably.

11 psi of boost raises your ambient air by 140 degrees F. You should be reading close to 240

The LLY's are overheating in tow application because the turbo is outputing over 500 F (over 220 degrees inlet air)! The CAC was not designed to resolve that.

Just FYI

11 psi of boost raises your ambient air by 140 degrees F. You should be reading close to 240

Not according to my truck with the Tech2 reading the parameters.

185 to 187 deg F max IAT at 10PSIG boost in a 88 deg F ambient.

Remember that a boost pressure of 10PSIG is only a pressure ration of 1.7 for the compressor. This SHOULD be the "sweet spot" for the stock GM-8 turbo, since it is factory range of boost pressure. With all of this said, I have yet to find a compressor map for the GM-8...

I'd say you either have an 90% efficient turbo (unusual), or an error. We'll just go with the former.

The 6.5 world is new to me, so if the turbo is especially efficient, as it was designed for low boost, non-intercooled, that it just might be.

Where is your IAT measured, maf sensor?

I'd say you either have an 90% efficient turbo (unusual), or an error. We'll just go with the former.

The 6.5 world is new to me, so if the turbo is especially efficient, as it was designed for low boost, non-intercooled, that it just might be.

Where is your IAT measured, maf sensor?

My IAT is in the stock location, as far as I know. I have not moved it. I will check for the proper location, though...

I would like to lay my hands on the compressor map for a GM-8 turbo, if any has one they would like to share...:D

what I meant was, is your iat measured at the air box, or post turbo?

If airbox, you are comparing apples to oranges, and charge air is over 300 F (I don't know if the 6.5 takes intake from underhood or a cold air source, if your underhood airbox temps are 190, you have issues maybe

If post turbo, then we are back on the same page.

OK, when I say what boost I have, I mean what I see when I look at my autometer gauge saying 11 psi. The computer says 15+11 or 26 psi. That is also running the 3 bar map. Now, when I go and run my truck, I hook up mt matco scanner, go to live datastream and then with the truck just warmed up, I do a holeshot. The truck is a dog at first, lots and lots of black smoke, then the truck kits it up with 11 psi, still black smoke and about a half mile later at about 70 miles an hour, 150 F IAT, stock IAT location.

Why do people get 19-21 psi out of the GM-8 if I only get 11? How is that?

You could have a leak on the crossover or at the exhaust manifold to block surface gasket.

What's closing the waste gate? if it's the vac system, I'd think it was to blame.

Consider the waste gate plugged. I have swagged an aluminum plug into the hole. It ain't comming out. I interference fit the glug .010, shes stuck good and will exhand with the heat now. I did have a home made turbo mater.

The crossover has all new donuts and is not leaking at all. The exhaust manifolds have all new gaskets too. No exhaust leaks for me.

QM, what do you think the boost should be at, if I may ask?

Over 20 psi at WOT if all conditions are right. 300* F IAT uncondensed.

Put a charge-air cooler on it, tow a 5-10k trailer................

Got my boost, 19 right now, still fixing the boo-boo. I have a slit in the boot conector turbo to manifold. I could always hear the hissing, that is why I though the turbo was maxing out. It turns out to be the boot was ripped and with a little duck tape, I got 19 psi. I will have to go to the truck stop tomorrow and see if they have the hi-temp silicone connectors that I need. But hey, she ripped a good run:D .

Sorry, this is a little late, but a boost leak tester is easy to make. Go to the hardware store and buy a rubber fitting that matches the intake side of your turbo, with the other end necked down to accept a pvc bushing. Reduce the bushing size to allow the installation of a tee, on one part of the tee put a 0-50 or so pressure guage, on the other side, a fitting for compressed air. Regulate your air pressure to about 25 psi and hook it all up(don't forget the hose clamps) this will find your air leaks, a very usefull tool especially when you get your intercooler hooked up and have more places for leaks.;)

IAT needs to be measured at high boost levels.

Manifold throat diameters of the 6.5 limit pipe size. If you want a large pipe go for it, but all you are doing is adding a ton of unnecessary volume to the pipe.