GM-8 vs. GM-4 turbo?

[arveetek]

I bought a '97 parts truck a while back. It has the desired cooling upgrades, free-flow intake manifold, etc. It also has the GM-8 turbo. My '95 has the GM-4.

Would it be worthwhile to swap my GM-4 for the GM-8? My Tahoe is my daily driver, that I use occasionally to tow my small camper or my Jeep on a flatbed. I'm pretty pleased with the performance now, but since I have a GM-8 staring back at me... My GM-4 spools quickly to 9-10 psi, but starts to drop off at higher RPM. Any more boost than that and my PCM gets unhappy.

It looks like the waste gates are different between the two as well. If I did swap, could I modify my GM-4 Turbomaster to fit the GM-8?

Thanks,

Casey

[arveetek]

I should also mention that whether I swap turbos or not, I will be swapping over the non-EGR intake, the '97 airbox, and purchasing a Flowmaster crossover pipe, 3" downpipe, and building my own 3.5" exhaust.

[DaveBr]

I did the non EGR manifold switch on my truck. I swapped out the computer as well so it would not throw codes. I also bolted the EGR valve back ontop the non EGR upper manifold so everything looks functional. I also left the mass air flow sensor installed. I just removed the guts so it would not restrict airflow.

If you want more boost you will have too get a reprogramed chip or buy a boost fooler.

Out of the two turbos I would run the one with the least miles on it as long as it passed visual inspection and had no play.

My old truck was a 93 and it was by far more superior in power and milage than my new one. On the upside the 98 has been trouble free for a long time.

[arveetek]

Out of the two turbos I would run the one with the least miles on it as long as it passed visual inspection and had no play.


Thanks for the reply!

Of the two, the GM-8 has about 100K less miles on it that my current GM-4. However, the '97 with the GM-8 has been run hard and put up wet! It was used as a city maintenance truck. It only shows 100K on the clock, but it sat around idling for long periods of time. The engine is bad, as I believe it has a broken piston. It runs but has no compression on cylinder #1.

I would trust my 200K mile GM-4! It's been taken care of very well.

Casey

[john8662]

From what I've read, the GM turbos all have the same compressor wheels and turbine wheels. The only difference I've heard on the GM8 is that is has a little larger A/R on the turbine housing itself. Nothing to verify this. It does have a better flowing turndown casting than the GM1-4's though.

The turbomaster from the -4 won't work on the -8.

[HH]

I went from a 3 to an 8 and my truck tows MUCH better with the GM8 turbo. I would make the switch.