Turbo Swap Question

[duallypilot]

Curiosity question here - Other the the waste gate operation, is there any difference in the 6.5 turbos used from 1993 through 1997?
I'm thinking of swapping the turbo off my 93 6.5 with the one off my 97 6.5 since I bought the older turbo new and know it's history and I don't know anything about the 97 turbo since we've only had the truck a month and I'm going to part the 93 out anyway. I had installed a Turbo-Master when I put the new one on the 93, so that would eliminate me buying another to install on the new truck.
Looking at the pictures online, I can not tell any noticeable difference between the years.
Thanks in advance for any help.

 

[countryboy69]

There are 3 turbos used over the years. GM3, GM4, and the GM8. Your 97 should have the GM8. Your 93 should be a GM 3. There are a small visible difference on the wastegate setup but many more differences inside. If your not worried about performance at all and really just want to save the cash you could run the 3 but it will NOT run as good as it used too!

 

[Jorge6.5]

The gm3 is the worst of all and a complete waste of time swapping it in when there are many other turbos out there that can be had for reasonable amount of money

 

[Jorge6.5]

If funds are an issue just keep running the turbo on the 97, it should be the gm8 which in fact flows the best out of all the gm series turbos. If not already, put a 4in exhaust on your truck to help the turbo breath.

 

[THEFERMANATOR]

There are 3 turbos used over the years. GM3, GM4, and the GM8. Your 97 should have the GM8. Your 93 should be a GM 3. There are a small visible difference on the wastegate setup but many more differences inside. If your not worried about performance at all and really just want to save the cash you could run the 3 but it will NOT run as good as it used too!

Close, the GM-3 and GM-4 are basically identical except the 3 was used from 92-93 and didn't have the vacuum wastegate(just a spring inside of it) and the 4 was used from 94-95 which added the vacuum operated wastegate. 96 brought about the GM-5 which uses the differently mounted vaccum canister, but only a slightly larger exhaust housing. Mid year 98 they went to the GM-8 which looks like the GM-5, but has the largest exhaust housing of all of them and is the prefferred factory turbo to run. And then there was the GM-6 center mount in the vans and hummers from about 96 on.

 

[ak diesel driver]

I have a gm6 on my 96 so not all of them are center mount

 

[L98TPI]

Close, the GM-3 and GM-4 are basically identical except the 3 was used from 92-93 and didn't have the vacuum waste gate(just a spring inside of it) and the 4 was used from 94-95 which added the vacuum operated waste gate. 96 brought about the GM-5 which uses the differently mounted vacuum canister, but only a slightly larger exhaust housing. Mid year 98 they went to the GM-8 which looks like the GM-5, but has the largest exhaust housing of all of them and is the preferred factory turbo to run. And then there was the GM-6 center mount in the vans and hummers from about 96 on.

My 96 came with a GM4. When I say "came with" I mean it was in the back with the rest of the top end of the motor. maybe this was an early one? Or the state monkeys just put on what they had on the shelf?

 

[Jorge6.5]

My 1996 truck came with the gm5

 

[ak diesel driver]

my 96 dually has a gm 5 also. it came with the low flow waterpump and single stat. the gm6 on my dd has the ho waterpump and dual stats

 

[buddy]

For clarification, they are all the same turbos. The only difference is in the exhaust elbow and wastegate actuator. The exhaust housing is the same 9cm^2 on all of them, but the housing is longer on the GM3/4 because the wastegate is in the housing, and it uses a cast cobra 90 degree elbow. The later turbos they put the wastegate lever in the exhaust elbow, so shortened the housing (making it actually smaller "housing" with GM8), but a larger smooth 90 degree cast exhaust elbow.

they will all perform very similar. Just potential flow benefit of a smooth 90 vs the cobra 90 elbows. Better to use a differnt larger turbo if within means.

 

[great white]

Re-posting something from GMCTD of another site from a long time ago that may or may not be relevant. I'm not saying one particular turbo is better than the another. Just puttin' the info out there. I accept no responsibility for it accuracy (or inaccuracy):

Second off - The GM-8 is a definite improvement over the GM-4 on both ends.
Decreased EBP post-turbine, pre-turbine, and increased compressor efficiency are resulted.

The wastegate assy in the GM-4 turbine 'snail' was relocated to the exhaust elbow in the -8.
The reduced 'snail' length allowed opening up the exhaust adaptor elbow by removing the 180deg fold-back
Also opened up the wastegate exit path, allowed freer wastegated exhaust flow.

Result : lower EBP in the elbow, post-turbine, increased flow thru wastegate, and reduced EBP in the turbine.
Not insignificant, when combined with a freer flowing exhaust system and upgraded PCM.

A radial, or centrifugal, compressor housing usually consists of two parts - the scroll housing, and a plate to seal the open side, which is also attached to the center section containing bearings, wheels, and drive shaft..
The plate acts as part of a diffuser, which creates pressure by reducing the gas velocity after it slings out of the high-speed impeller wheel..

The GM-4 is of the parallel-wall diffuser type, meaning the scroll is cast in two pieces, with an integral vertical separator, which will be parallel to the main sealing plate, but spaced apart from it at a dimension depending on designed flow rate and pressure ratio
The -4 compressor has a multi-stepped inducer throat area, and is limited to a more specific flowrate range by the dimensions of and between the parallel walls.

The -8 is of the scroll-diffuser type, where the shape of the scroll acts as the diffuser, and which, with the inducer throat steps removed and smoothed, is more efficient over a broader range of engine flowrates.

The inducer throat area is where linear flow into the compressor begins to whirl, in anticipation of becoming radial flow into and out of the spinning wheel.
Any turbulence here, as caused by the stepped -4 surfaces, can mean easier 'stall', where the compressor wheel, spinning faster than inlet air flow rate, begins to cavitate.

Turbine rpm surges as load decreases, and - well....exploding turbochargers are not generally considered spectator sport.

A compressor wheel and a turbine wheel may be used in various sized housings for various flow rates and pressure ratios, where even the shape of the housing will raise or lower the expected output.

Or, various size housings may be used with same wheels to alter turbocharger output, as required, desired, and inspired..

So - it may be seen that the GM-8 is of improved efficiency over the -4, even with the same size and shape wheels.

Remember - science, without reason, makes no sense.

 

[L98TPI]

my 96 dually has a gm 5 also. it came with the low flow waterpump and single stat. the gm6 on my dd has the ho waterpump and dual stats

My 96 is HO pump and dual stats also. With the GM4 turbo (maybe original)

Good info greatwhite BTW.

 

[great white]

My 96 is HO pump and dual stats also. With the GM4 turbo (maybe original)

Good info greatwhite BTW.

GMCTD almost touches on a point that has long been a pet peeve of mine and that's exhaust rejoin downstream of the wastegate.

Almost every OEM does this very poorly in a wastegated turbo design, which results in "backpressure" in the exhaust.

Really, how much trouble would it be to at least put a "splitter" and smoothing the rejoin between the wastegate and the turbine exit?

A little extra casting material....ah well, gotta cut corners where you can when chasing the almighty buck I guess....

 

[buddy]

Although with my GM4 I was recording lower backpressure values than those reported by user with a GM8, could have been a gauge differnce, but differences were significant. I dont think there is a significant differnce between the 4 and 8, at least they are the same housing size, whether or not one flows through the same wheel better I wouldnt speculate on. The GM4 wastegate opens up into the elbow quite nicely, not a big difference there from the 8, only where the gate pivots from, the housing of the 4 and the elbow of the 8. The cobra head is not a bad elbow design when it come to a 90 degree bend, especially if it starts out turbulent anyway from an open wastegate and wheel flow merging in the same space.

I dont recommend spending money on either one! Get something bigger.

 

[duallypilot]

Thanks to all for the education and information. I'll be looking into a larger turbo now later down the road after the exhaust and computer is upgraded.