reboring my 305 V-8 engine

[Alex_W]

Hey I want to rebore my cylinders in my V-8 305 engine to a 350 but the thing I want to know is if i do that, would there be a diffrence between that and a manufactured made 350 engine. I don't even know if this is worth it but I am just brainstorming some ideas. Does anybody know?

[abaird]

305 = 3.740" x 3.48"
350 = 4.000" x 3.48"

I don't think that is possible. Engines that are bored on the extreme side tend to overheat easily. I wanna say that the most you can bore a cylinder is about 0.080" I would just buy a 350.

[MagicRat]

Originally Posted by abaird

305 = 3.740" x 3.48"
350 = 4.000" x 3.48"

I don't think that is possible. Engines that are bored on the extreme side tend to overheat easily. I wanna say that the most you can bore a cylinder is about 0.080" I would just buy a 350.

This is absolutely correct.
GM used smaller cylinder cores when casting a 305 (as compared to a 350 casting)
They did not use 1/4 inches of extra cast iron in the cylinder walls, so there is no extra iron to remove.

[curtis73]

Correct. The thickness of the cylinder walls is about the same on both blocks; about 5/16". So, if you tried boring a 305 by .265", you'd have surpassed the safe 1/4" required for rigidity, combustion pressure, and block rigidity. Even if there were enough meat, it would cost more to bore it out than to buy a brand new 350 block. They're available for $200 these days.

The most you can safely bore the 305 block is .060" over. Its possible to do more if you sonic-check the bores for core shift, but usually no more than .060".