GM 4 turbo vs GM 8 install & performance?

[Crankme69]

Couple of questions about these 2 turbos.

Hunting on the net last I read there is NO difference in performance from the GM 4 vs GM 8 turbo, is that true?

Installing a GM 8 in place of my GM 4 what mods are needed?

TIA 69

 

[1995yukon65]

the only difference btwn the 2 turbos is efficiency. the gm-8 spools up quicker and flows slightly smoother. If you have the choice put the gm-8 in. no mods are needed to switch btwn the two turbos.

 

[buddy]

There is a difference is wastegate actuator position, and I dont expect GM8 spools faster, I think it is slightly larger compressor, so more efficient at higher boosts.

 

[JiFaire]

There is a performance difference between the 2 turbos, largely in terms of exhaust flow restriction and the design of the compressor - as was stated earlier, flow is slightly better in the GM-8.

The biggest difference though, is efficiency - due to differences in the elbow and in the flow design, the GM-8 will generate equivalent boost volume and flow at lower backpressures, and with lower IATs (important factor).

 

[docdray]

swapped 4 to 8 on my 94, seems to run a little lower egt than the 4, and spools a little quicker. I agree, newer design is better. fab'd new boost controller and works good.

BTW, have noticed less black smoke, see above reasons. I think I paid less than 500 from pensacola due to recommendations here (TDoc)- no problems

 

[Crankme69]

Thanks for sharing the info & to all the replies.

Here is a quote from gpopshop.com/dieselturbos.html:

"GM/Chevrolet 6.5 Diesel
Spec #'s GM-1, GM-3, GM-4, or GM-5/GM-8

GM Spec #'s 1, 3, and 4 are all interchangeable and are direct replacements for each other. GM-5's and GM-8's are also interchangeable and direct replacements for each other. You cannot install a GM-1, 3, or 4 in the place of a GM-5 or GM-8, or vice versa, without modifications. There are no advantages, as far as performance, from one spec # to the next. All of these turbos use the exact same compressor wheel and turbine wheel. The only differences in the turbos are the outward designs and wastegate actuator locations."


I'm not in any way shape or form doubting any of the info posted here that the GM 8 flows better then the Gm 4. Just thought I would disclose the source of the info that prompted my comment in my original post.

 

[JiFaire]

Look at the exhaust outlet side... the differences are on that end of things. Visually, there is significant difference between the elbow on the GM-3 and the GM-8. The inlet housing is also slightly different, IIRC - pretty minimal.

Like I said, efficiency. A GM8 will have much lower IATs and backpressure at equivalent flow volumes than a GM3

 

[Crankme69]

Makes me wonder if the GM 8 exhaust spool would bolt on my GM 4?

 

[Odlaw]

Don't know if they just made a typo or what but I will have to call "BS" on the part about there not being any difference in performance between the spec numbers......and the part about them not being interchangeable is probably referring to the wastegate control. I just replaced my GM-3 with a GM-8 - no problem swapping - bolts right up - took less than 30 minutes. GM-8 spools up noticeably faster(and at lower rpm) than the GM-3 and it spools down a lot slower (that suggest to me it's more efficient). The exhaust 90 degree elbow on the turbine is where the big difference is - GM-3 is folded over with a nice 'kink' in it, the GM-8 has a nice smooth bend to the 90.

 

[Crankme69]

Yea but maybe I just read it wrong...it's somewhat vague the way it's worded. I have noticed a few GM 8 turbos on fleabay worn ones for cheap and if all I had to do was change out the exhaust spool onto my GM 4 that would be cool...Then I would have my very own GM 48 LOL :33:

 

[ak diesel driver]

The compressor end is also diff IIRC

 

[JMJNet]

Yes, you can swap it directly.

 

[Crankme69]

Yes, you can swap it directly.

Excellent! Thanks for the reply, I'll have to keep my eye out for a GM -8 core for cheap. I'm gonna pull my turbo off this spring & go through it, be a good time to swap that exhaust spool out.