GM Turbos???

[taznj63]

I would like to know any nad all info on the GM turbos... I have a GM-1 on my 92 and want to know if it is good or is one of the others better? Is there a GM-2,3,4..thru 8???
What are the differences?
Thanks for the info...

[cruzer]

Taznj63, I don't know much about the turbos other than from past post, and it seems the GM8 is the desired turbo ,but there are slight mounting issues.

The reason I'm chiming in is, we have similar engines/trucks except for 4wd. My 1st mod was the stinger system which gave good increased power. The balance of my mods were all done at 1 time, so I don't know the individual effect that each one has. I do know it's like a different truck. I have a ton more power. I pull abount 8500lbs. With the stinger system only, I would have to make runs on the hills of KY. & loose speed towards the top. Now, I can just set cruze on 72mph and there is minimal fluctuations in speed. Maybe I loose a couple mph if any. I did turn the new pump up an 1/8 turn and set the turbo master around 14psi, EGT 950* on the biggest hill and it pretty much holds its speed. The TM seems to be more responsive than the longer arm of the stinger system
FYI.

If a GM8 were to fall in my lap I would have to put it on, but then there are issues w/the turbo master mounting to it.

[Randee of the Redwoods]

Dont' know much either. There is a 1, 4, 2 I think, and 8. There may be a 6 as well. All just revision indicators really. I have a 94, came with the 4. I swapped out for a nice used 8 unit. Fits perfectly, no mods needed. So I was told, the 8 unit is desirable for towing due to it's slightly revised wastegate houseing for less back pressure at high revs. I was also told it's boost came on JUST a hair later than the early units for a better power band in the upper revs for towing/hauling. I can't tell the difference in the 2 really and probably won't know until I tow. The biggest difference so far was the exhaust.

[gmctd]

To enhance the previous posts -

For the GM-5, the turbine housing was redesigned to promote exhaust flow and reduce back-pressure.
The compressor housing was also redesigned for increased flow and compression efficiency.
The cartridge was modified in turbine and compressor flange dimension only.

Minor change in the GM-8 to the wastegate shaft bushing - increased in length to reduce early wear failure.

GM-8 offers improved performance over the early versions. It's not heart-stopping performance, but the increased efficiency helps, reducing IAT and EGT levels below that of the GM-1 thru -4.

If you need to replace one, opt for the -8.
Some modification to the wastegate controller mounting bracket is necessary, but not difficult.

[Randee of the Redwoods]

Hey, gmctd, what mods you talking about? The swap on my 94 K3500 was direct. The turbo fit nicely and contacted nothing. The wastegate bracket also needed no change. The only thing I did when swapping the turbo was to remove the inner fender liner. Makes the job 100000000000000000 times easier.

[taznj63]

So from what I am reading the GM-1 is not the turbo of choice as the later versions have been improved and modified as to promote better applied boost.
I can sustain 13-14 psi on hills with this turbo and on straight highways it is around 5-7 psi at 60-70mph. Now when cold (after startup engine cold) my max boost is 6-8 psi until engine warms up. Not sure if it is because of GM spring return on wastegate letting go early or what.
I am planning on upgrading to 97 cooling and 21" D-Max fan/clutch, injectors, gear drive timing, and possibly a new injector pump for more ponies.
If anyone has done 97 cooling mods on mech injection I would like info on what you did with the throddle cable brackets and any mods to dual t-stat crossover.
Thanks to all...

[gmctd]

Randee, his truck has the mechanical wastegate controller - has a spring in the cannister, where the EFI turbos get a vacuum diaphragm.

His controller, and up to the -4 vacuum controller, is mounted in a low, horizontal, front-to-rear configuration.

Some modification is required to install that cannister and control rod on the later series turbos, and particularly so on the -5 and -8 versions, where the cannister is vertical, above the wastegate arm.

The modification is no hill, for a stepper.

Glad to see your upgrade worked out ok.

[Randee of the Redwoods]

Ahhhh, gotcha. I did see his was a 93, but then I threw myself down a flight of steps so I didn't realize his wastegate was not computer controlled.

[cruzer]

tanzj63, I did the cooling mods to my 92. The best advice to you is get "The 1999 Feature
Articles & product Reviews" from TDP. When you order it be sure to ask for the supplement too. This info tells all you need to know. It also has other good info on mech inj and glow plugs.
I use it quite often. It goes in detail on the T-stat housing & throttle cable bracket. The book has a blueprint of the bracket, but it is like 10% smaller than actual size, so I scanned it and reprinted it 10% larger and used it for a template. You make the bracket out of something like 14ga sheet metal. There is some welding required and cutting of the original bracket. I could't weld the alum housing so I found a shop to do it for me for about $25. Its a little time consuming ,but not difficult.

FYI, I put on the 20" fan and clutch and it works great. From What I recall there's not much diff in the two. Doesn't the 21" fan bolt to the spin on clutch? I can't remember why I opted for the 20" fan, but I know there was a reason.

Hope this helps.