Some 3100 boring/machining performance questions.

[Drunken Sailor]

Hey guys, I'm new here. I just discovered this website and it looks the THE place for the 60* V6 enthusiast. I'm a GM FWD performance nut, but my background is in building and racing L67/L32 (3.8L Supercharged) and now LS4 (5.3L V8 ) engines. I recently came across a '95 Grand Prix Special Edition with the 3100 that I would like to use as a winter/second car.

I am planning a complete rebuild on the 3100 but would like to take it up from it's somewhat low 160 HP to somewhere in the 200's. The engine has 200,000 km on it and I would like to build an engine reliable enough to run that distance again with no major problems. I'd like to acheive most of my gains in the machining/internals area, not with bolt ons, since I will be replacing or servicing pistons/crank/rods/cam anyway.

I've been reading about the .120 overbore that takes this engine to the same bore as the 3400. I know on most GM engines, .060 is the maximum bore, and this is twice that. The 3800s can be bored past spec with little problems, but how about the 3100? Boring over the 3100 and installing 3400 pistons and rings sounds like an (maybe too) easy way to increase compression and power a bit.

This is just an idea that came to mind. I'm going to hang around here and learn more about these engines, and I'm sure the site will be helpful with my rebuild. If anybody would like to share some ideas/methods used to achieve a little better power from a 3100 through machining and internals, please do. Thanks guys.

[bszopi]

In all honesty, you'd probably be better of finding a junked 3400 and using it as a starting point. 0.120" is alot to be taking out of an engine, let along an engine with 200,000kms on it. I'm assuming you live in Canada since you are listing it as KMs, so I'm not sure on pricing for 3400s up there, but I know you can find low mileage 3400s down here usually for under $500. And by starting with a 3400, you get a much better top end as well, which will help put you to (and above) your current HP goal.

[Guest]

In all honesty, you'd probably be better of finding a junked 3400 and using it as a starting point. 0.120" is alot to be taking out of an engine, let along an engine with 200,000kms on it. I'm assuming you live in Canada since you are listing it as KMs, so I'm not sure on pricing for 3400s up there, but I know you can find low mileage 3400s down here usually for under $500. And by starting with a 3400, you get a much better top end as well, which will help put you to (and above) your current HP goal.

Starting with a 3400 will be the best option.

Rated from GM highest rating were in the mid 180s for HP, with stock manifolds, and all intake restrictions in place.

Opening up the exhaust (headers) and having a more free flowing intake system should yeild close to if not above 200 HP, P&P and/or properly matched cam, will help even more to achieve the goal.

[EspanolaGuitarista]

Another question....

Does overboring unshroud the valves any or is it negligable?

[geoffinbc]

Yes it does in all engines. However the Gen II and III engines do have splayed valves which also aid in un shrouding.