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5,030 Posts
Building a '67 Sportside P/U

Building a 292 Turbo, Injected on E85 and Laughing gas
I'm gonna go out on a limb here and say you're talking about a Chevy inline 6 and not a SBC or FoMoCo V8.

What is the safe bore of this engine?

Starts with a 3.875

Can it go to 4?
Very unlikely. You can get a 0.060" overbore safely in most cases, but pushing it to 1/8" is risky and I wouldn't even think about trying it w/o a sonic bore thickness test to see how much material there is in the block- and where the material is located (thrust side of bore or not, for example) due to core shift and manufacturing tolerances.

If this is a drag only deal, you might consider a partial fill of HardBlok to stiffen the block, but even then, at 0.125" over, there's just not going to be enough bore thickness IMHO.

If you're boosting it, forget about pushing the limit of bore size. What you need is a stiff bottom end.;)

878 Posts
Agreed with cobalt327. However, in the '70s, we built a 250 and bored it .125" over and it was fine. A sonic test WOULD show what you need to know.

Just went through a 292 for a work truck. .060" over was the largest available.

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