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The 3.1L and 3.4L V6's are great motors. Mechanically identical other than the bore size. The 2.8L was the same but it had an aluminum bodied oil pump that seemed to wear out and take the motor with it. So they were not as reliable as the 3.1L and 3.4L which had all iron pumps and improved crankshaft oiling. They are one of the best and most used Chevy V6 engine. Their production run lasted 30 years so there is lots of parts and support. One day I wouldn't mind a late 90's 3400 engine in the trooper. I have been contemplating 14:1 compression and propane too. But for now my rock solid 3.1 serves me well.
 

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The 4.3L 5.0L and 5.7L all used the same throttle body. So it does not matter where you find it. Just find one with a tight throttle shaft. I like using the later model cores because they all have the bolt holes for the throttle cable bracket.

The Isuzu version of the GM V6 is actually a Lumina Van engine with an S-10 intake. That is the easiest easiest way to describe it.
 

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The worst thing about the TBI motors was weak cams and low compression. This is true for the V8'S too. If you can get compression closer to 10:1 and get the much healthier cam it really wakes up the motor. More so than external bolt ons that's for sure.

I never had time to CC my engine but from rough calculations I am just over 9:1 compression with mildly ported heads and gasket matched ports and intake. With the comp 252 cam it has lots of grunt to 5500 RPM and I can rev to 6000 if I feel like it. But I built the engine for off idle torque and it does that very well. My 2.8L was fine on the road with 33's. I even had it pulling my utility trailer on some serious highway hills but I was down in 2nd at 4000RPM. With the motor I have now it hauls even more weight in third up the same hill and I usually sit at 3500 RPM doing 50MPH up the hills. I can go faster by tipping into the gas but I don't like winding it out for that long even though I'm confident it can take it.

Thhis engine family take a lot of hate because early 2.8Ls used to spit main and rod bearings and they made even less power. However once they were ironed out they were as reliable as a nail. But they still took crap for being low on power. But feel free to point out to anyone that they made more hp per liter than any of the V8'S offered at the time.
 

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Stock for the 3.1L was 8.8:1 If I remember right. But that's advertised so who knows how much it varied.
 
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