Turbo ? GM-4 to GM-8 change over

[chevytrucksonly]

Need some knowledge/experienced based feedback about changing over a GM-4 to a GM-8 on a 1994 6.5;

1) Is there any performance or benefits with going from a GM-4 to a GM-8?
2) It seems physically that the GM-8 has a larger chamber and exhaust neck prior to the downpipe flange? Is there any other difference?
3) If I do make a change over on my 94, what will I need to do as far as operational or set up changes. It seems to be a straight change over, but what about the vacuum set-up, add-ons or alterations or anything else?


Thank you
MDS

 

[daustin]

I swapped out my Gm-3 on my '93 3500 with a GM-8. I noticed that it built boost quicker and seemed to have more power than the -3 i was running. The GM-3 and GM-4 are very similar, both have a restrictive "bend" in them. When i changed mine out, it was a direct bolt-in deal. Only thing i had to fab up was a spring waste gate controller like the -3 had as the -8 is vacumn based. What i did was cut the vacumn tuna can open, got some rod fro home depot, threaded it and used a spring off a drum brake hold down. You'll need a boost guage to accuratly set the boost. When I first fired it up with the -8 it ran up to 16psi QUICK, so some adjustment was needed. lol
One of the best things i've done to my 6.5 TD.
Don

 

[bk95td]

About the only difference hooking them up is the gm8 has a larger vacume hose nipple. Yes a gm8 spools faster.

 

[tanman_2006]

From what I have been told it is a straight change over, I had one but ended up trading it for something else before I could try it out. The exhaust side flows smoother and has the potential to reduce EGT's, you are right the change in design is where it flows into the down pipe.

 

[kimagine]

From what I have been told it is a straight change over, I had one but ended up trading it for something else before I could try it out. The exhaust side flows smoother and has the potential to reduce EGT's, you are right the change in design is where it flows into the down pipe.

I have to agree with the above statement. If you were to go with a turbo master, you will need to cap off the vac line running to it and verify where your spring is set as well as which hole to set the bolt. I too want to get a better turbo for my 94 beit a GM-8 or even better when the funds allow, an ATT!

 

[buddy]

The location of the vacuum hose nipple is different since the wastegate actuator is vertical on the GM8 vs the GM4. But that doesnt matter when using the vacuum setup.

The cobra head on the GM4 isnt so bad, its designed to limit turbulence on a tight bend. It flattens the air in the same cross sectional area so it doesnt swirl and then expands again back to circular cross section. I'm not saying that the GM8 isnt a little better, if its free or has to be replaced the no need to keep the GM4. Its just not one of those things I would pay to change if the GM4 was working fine. Better investment if someone needed a new turbo or wanted an upgrade would be a larger turbo.

 

[DieselCash]

I transfered a GM-3 to a GM-8 with a turbo master and it was easy. No problems and no issues, direct bolt on item.:thumbsup:

 

[Turbine Doc]

It still working good for you Marty ?

MDS if shopping for a new turbo best direct fit bolt on setup is the ATT turbo sold here at discount to TTS members through Walking J Designs one of our site vendors, not only is it plug & play install but it eliminates the vacuum boost regulation system that can leave you stranded.

 

[chevytrucksonly]

It still working good for you Marty ?

MDS if shopping for a new turbo best direct fit bolt on setup is the ATT turbo sold here at discount to TTS members through Walking J Designs one of our site vendors, not only is it plug & play install but it eliminates the vacuum boost regulation system that can leave you stranded.

Thanks for the info will check out
MDS

 

[DieselCash]

It still working good for you Marty ?

MDS if shopping for a new turbo best direct fit bolt on setup is the ATT turbo sold here at discount to TTS members through Walking J Designs one of our site vendors, not only is it plug & play install but it eliminates the vacuum boost regulation system that can leave you stranded.

So far so good, I have not driven it in over 6 months. The wife has not complained any.

I will be home in less than 10 days, cannot wait to drive it.