Chevy 350 bored 40 over. Does that change the timing mark from where the stock timing mark is?

A 350 bored .40 over makes it a 357, the timing for this motor with a mild cam would be 10-12 degrees.

The timing mark itself would not change due to being bored oversize. However depending on what other modifications have been made the base ignition timing may need to be adjusted to make the motor run at its best. Like btemple said if it has a mild or RV cam you may find it runs better if you set the base or idle timing at about 12 degrees before top dead center(with the vacuum advance unhooked and the engine idleing). But just boreing the cylinders oversize would not change the timing. You said it has high compression heads. This may cause problems if you advance the ignition timing very much. High compression can cause detonation or "pinging". And to much timing advance will also agravate this. If you have flat top pistons this also raises the compression ratio. Dished pistons lower it. You definately need to run premium fuel to get the most out of this engine and to keep it from "pinging" and destroying itself. I am also curiouse why you rebuilt thye top end. Did you have a blown head gasket? If so that could have been caused by the high compression and "pinging". One last thought we are both assuming that you meant ignition timing mark here. If you meant camshaft timing marks on the timing chain set then that is a different ball game. Give us more details if we haven't answered your question right.

This answer was edited by Monogyny644 47 days ago.

Reason: spelling