307 Olds pistons in Buick 231

[Red79Rat]

Okay so I don't know if this would be better suited in the Before Black section but I think I will try it here: After some thought I have decided it would be fun to see just what kind of fuel economy I can get out of a carb'ed normally aspirated 231. I have decided on going with a COMP High Energy cam (252 advertised/.425 lift), an Edlebrock Performer intake and some custom grinding on the stock (1979) heads. My main question is about pistons, the engine is currently all stock and has 127,xxx miles on it so I'm sure it would be for the best to clean up the bores and probably go ahead and do a .030 overbore. Obviously that means new pistons so here is where my problem comes in: I know higher compression equals both more power and better engine efficiency. The only pistons Summit racing has for a 231 are dished but they have some flattop Olds 307 pistons, I have heard they interchange but I'm not sure. Also what carburetor would you recommend, I'm leaning toward a 450 vacuum secondary Holley but is there a better choice? Remember I'm building this for optimum fuel efficiency so power isn't a huge priority but I do want good throttle response. My goal is 25MPG highway, and somewhere around the 180 horsepower mark. I assume that's a fairly realistic goal so do you think my plan will hit that? I will be running a 200-4R transmission and the stock 3.08 rear gears. Any tips and advice are appreciated. I do also want to try to keep this build under $2500 and its got to run on 87 cheap gas. Thanks and God Bless

 

[TurboDave]

For mileage I would much prefer a Q-jet or a spread bore holley.

 

[charlief1]

Get a stock 4.1 intake and use a Q-jet like Dave said. The smaller primaries will give you good response as well as better mielage.

 

[bison]

I would go with a really small stock replacement cam and advance the piss out of it if i was looking for economy. 180hp will be tough. Id convert to fuel injection with a 3800 series 2.

 

[Red79Rat]

JDPolzin saw this thread and offered to sell me a set of .040 over hyper' pistons, a 4.1 intake with a Q-Jet and an old 204/214 cam for pretty cheap. Does this sound like a pretty good start to my build?

 

[charlief1]

It would work fine. Also go to the B4black section and you can see how to mod the intake and make better power without killing gas mileage. It's a sticky so you should find it easily enough.

 

[77amc]

In my old "how to hotrod a V6" it stated to use the stock 3.0 piston in the 3.8 and that really bumps the comp. Near 10:1 since they're flat tops.
I can't do that since Im going with the 4.1 (040)

You know, i wonder if it would be comparable output between a .040 4.1 and a 030 3.8 using the 3.0 pistons?
In other words, if i do all this work to a 4.1 that's low compression, will it be the same HP level with a high comp 3.8 with same cam, intake, carb yadda yadda..

Thanks E

 

[ek02]

77amc, the 4.1 will have more power. More cubic inches and unshrouded valves with the larger bore work better than the 3.8. You can run more cam with the 4.1 than a 3.8 and still have a decent idle. That's been my experience with both engines. Red79Rat, if you want mileage, the Q-Jet is the way to go. Use the 4.1 intake and advance the cam for more bottom end. Find out what the lobe seperation angle is on that cam. I would want around 112 degrees LSA for mileage and a good idle. If you are going to use 87 octane fuel, you will be limited on the compression. You could keep the egr valve to limit spark knock. I had a loaded 84 Olds Cutlass with a stock 3.8 that got 24 MPG on the highway with a TH350 and lockup converter, so 25 MPG is reasonable. My Cutlass would not get out of it's own way though.

 

[novaderrik]

ditch the V6 and put a torquey 350 Chev in it if mpg's are your major concern.. maybe even step down to 2.56 gears.. with some tuning that's a 30 mpg combination that will have more power than the 231 will.

 

[77amc]

(Ppppsssssst.. Novaderrik. I just built a .060 283 with forged flat top pistons, Comp ex268, Vortec heads (self fully ported w/comp springs) aftermarket carb intake, Ruggles q-jet, 200r4 little higher stall, 3.73 yota rear in a long bed Mighty max.) Kinda excited to finally get it running.
The 4.1 might go into another 'project'
Trying to shoe-horn a LT1 into a 328i vert also.

E

 

[dr_frankenstein]

NA just sucks when it comes to the buick.

i wouldnt expect good gas milage,

it will be such a turd, your foot will be in it all the time. and right out the window went the economy.

A.j.