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gm3/gm8

chevyCowboy

chevyCowboy

I might be crazy but i ain't dumb
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Location
Springfield Nebraska
i found what i think is a gm8 on craigs list but the guys not for sure is the tag in the same place as it is on my gm-3 hes not asking 150 for it says it only about a year old. what differences are there between the gm3 and gm8
 
Good answers, guys.

GM-3 has a horizontally-mounted, spring-controlled wastegate actuator. GM-8 has a vertically-mounted, vacuum-controlled wastegate actuator.

The elbow in the GM-8 is less restricted and has a better radius which leads to a lot less backpressure and better flow... GM-3s will bog up pretty bad when you crank 'em down.

They also have the model stamped on 'em...
 
you can get a lot more boost out of the GM-X turbos, but they aren't effecient. Under heavy load, i boost my GM-3 up to 23-25 psi, but the EGT's get really high
Without a load, it falls on it's face around 3,000
like it was said, the GM-8 will flow better, but I don't think it's anything that you will really notice
 
so for 150 bucks would i see any better performance from my turbo (faster spooling, more boost, higher boost at sustarined rpms) i would like to put an ATT on but funding is limited and was wondering if this would be an improvement

any one have any imput on those heads?
 
Like has been said, you would see more efficiency, and perhaps faster spooling. I think you would get higher boost with lower EGTs, but I doubt you will see higher boost pressure.

Me? If the GM3 was working, I'd save the $150 and put it towards an ATT. One of those WILL give you much better performance. The other alternative is to look for somebody who has just changed their GM-8 over... put a note in the 6.5 'for sale' section.

I hate to see somebody buy a used part off Craigslist when you can't be sure how good it is...

Great price on the heads, IMO.
 
Non Typical said:
you can get a lot more boost out of the GM-X turbos, but they aren't effecient. Under heavy load, i boost my GM-3 up to 23-25 psi, but the EGT's get really high
Without a load, it falls on it's face around 3,000
like it was said, the GM-8 will flow better, but I don't think it's anything that you will really notice
Click to expand...


:eek: Holy crap! 23-25 psi?? Tell me your secret to getting these little gm-3's to make that kinda boost.


grasshopper is all ears. :D
 
I wouldnt boost a GM3 that high, too inefficient, backpressure would be horrendous, detremental.

With my GM4 and vac setup I get boost sensor pressure of 14psi and can sustain 11 psi up long steep hills.

I think you would notice a positive difference in at least efficiency, better fuel mileage, lower boost needed at high speed cruising. This would give you more power available at high rpms when you hit a hill. The same thing GM8 users see when upgrading to ATT.
 
buddy said:
I wouldnt boost a GM3 that high, too inefficient, backpressure would be horrendous, detremental.

With my GM4 and vac setup I get boost sensor pressure of 14psi and can sustain 11 psi up long steep hills.

I think you would notice a positive difference in at least efficiency, better fuel mileage, lower boost needed at high speed cruising. This would give you more power available at high rpms when you hit a hill. The same thing GM8 users see when upgrading to ATT.
Click to expand...

Beautiful thing is, you don't have to. :cheers2:
I know all of the above, and have to disagree that it is detrimental. Not to be an &%* but I did learn some stuff about it. It is inefficient, and that is why I am looking for the HX40.
But the fact is, it is still pushing more air then your GM-4 with it's setup.
I used a spring and wired it to the waste gate. I used different lengths of wire to adjust it.
Fact of the matter is, you can quite easily feel the difference in power with it the way it is, as opposed to boosting 12-15 psi.
I have a video of it sustaining 23+ boost up a rather steep hill while towing around 5,000 lbs, with egt's staying under 1000.

That being said, I know my exhaust pressure is incredibly high. But I am wanting to push this thing as far as I can. :thumbsup:
 
Non Typical said:
Beautiful thing is, you don't have to. :cheers2:
I know all of the above, and have to disagree that it is detrimental. Not to be an &%* but I did learn some stuff about it. It is inefficient, and that is why I am looking for the HX40.
But the fact is, it is still pushing more air then your GM-4 with it's setup.
I used a spring and wired it to the waste gate. I used different lengths of wire to adjust it.
Fact of the matter is, you can quite easily feel the difference in power with it the way it is, as opposed to boosting 12-15 psi.
I have a video of it sustaining 23+ boost up a rather steep hill while towing around 5,000 lbs, with egt's staying under 1000.

That being said, I know my exhaust pressure is incredibly high. But I am wanting to push this thing as far as I can. :thumbsup:
Click to expand...


That's cool - I guess I was always under the assumption that these turbos would only make 12-15 psi - and that was with the wastegate wired shut.

Are you reading those pressures on a boost gauge or some type of scan tool?

Thanks
 
yea, i have a boost gauge on there. put in on the same time i wired up the w/g. i know it works. with the w/g stock, it reads stock boost levels
like it was said, you will have really high backpressure and your egt's will go up quicker
 
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