Overbore...

[Silv6]

anyone overbore there 3.8? what kinda gains could you get?

[Dominic]

There is no room to do this.

[97 30th RS]

Wouldn't you be able to go .30 over and use Grand National pistons from JE?

[camaro_speedemon]

I just did a search about this yesterday actually. I found that overboring is pretty much good for only smoothing out the piston walls. The highest you can go is .030, not .30, and that's really pushing it. Anymore than that, your in the water jacket. The gains you would see would be very very minimal, something like maybe 1 or 2HP.

[Bliggida]

On a stock motor, no aftermarket changes. .030 over would break down to a 235ci motor. That would be worth 3 horsepower.

But on a motor making 250 horsepower. An overbore like that is worth 4 horsepower. In the overall scheme of things. Is it worth it? No. If you are going for that last little bit of power after you have exhausted every other option. Then this may be for you.

Also, if you want to figure in compression, since you'd be adding new pistons anyway. A 10:1 ratio on a 235ci motor, would be worth a total of 208 horses, assuming your engine was previously stock.

At a 250 horsepower baseline, 235ci 10:1 would give you a total of 260 horsepower.

Bore, stroke, and compression don't really become beneficial until you are past 1HP/ci. And at that 1:1 ratio, you'd need a serious overbore and stroke like that of a SBC's capability to be bored .125 over and stroked .125 over. (no you're not reading that wrong)

In our case, you'd really want to have 1.125 horses per cube before compression and boring would really make any significant difference.