How much noticeable difference does the GM-8 make over the GM-8? I have rebuilt GM-3, and worn out GM-8. Regardless, I going to get the truck running with the GM-3, but is it worth rebuilding the GM-8 and swapping it out later? What's the difference in the turbos, and how much real world HP and torque are we talking about?

I believe member "Dustin" has made the change, if I understand him correctly there is small improvement in EGT's but certainly no night and day difference. I still have the GM-3 and won't be changing unless the 3 gives me problems, I would however consider going to the much more efficient chinese turbo that Turbine Doc and Slim Shady are running and are planning to import. Thier talking several MPG improvement and free's up some hp and likely no intercooler is required because the boost air is much cooler. Sounds win win to me.

From what I read the GM-8 is more efficient than a GM-3.

Read on the other site about the ******* turbo. It is better than any Gm series turbo and cost about the same or less than a new GM-8.

Most of the change between the two is in the turbine housing, so the real gain, of a gm-8 over the 3 would be slightly better flow, so you'd see a slight mpg if at all noticable.

IIRC the gm-8 has a slightly larger compressor wheel major diameter.

Like I said, it'll flow more efficiently.

Thanks for the info. So it seems general consensus is run the GM-3 a while and upgrade to a more effecient turbo. Is the rear exhaust housing the main reason for the GM-X turbos being ineffecient?

Thanks for the info. So it seems general consensus is run the GM-3 a while and upgrade to a more effecient turbo. Is the rear exhaust housing the main reason for the GM-X turbos being ineffecient?

Kinda... It just works in a different rpm range, when gm marketed the 6.5 they ranted and raved about it's agressive low end torque, that was due to a turbo that worked in the torque curve rather then the whole hp curve. The higher the rpm, the more the engine flows, at about 12-15 PSI the GM-X series starts building backpressure at a higher rate to get a higher rpm hence why they have a wg, to flow more to keep the backpressure to compressed air ratio at an effecient rate, making them ineffecient at higher rpms when the wg is closed.

Stateman's mitsu turbo is also designed for a 6.9L (IIRC) diesel, so it flows more at higher rpms, with a bit of turbo lag in the lower rpm I would imagine.

Hey Stateman, have you dyno'd the truck before/after the swap to see how it's changed the torque and hp curve?

Last year i swapped my GM-3 for a GM-8 i got for cheap. The GM-8 built boost a lot more quickly than the GM-3, and seemed to build higher pressure overall. I could feel the difference easily and my EGT's were somewhat lower as well due to the more effecient housing on the GM-8 i think. My truck is a '93, thus toally mechanical and i did fab a "turbo-master" for both the -3 and the -8. If i had the same situation now, i'd do it again in a heartbeat. Aside from the waste-gate actuator being up/down on the -8 (the -3 is side to side) it was a bolt in operation. I checked the GM-3 when i pulled it off, it was in nearly perfect condition i later sold it on flea-bay and had a very happy buyer.

Don