Bored engine what octane?

[DTH]

If you bore your engine a couple times can you still use 87 octane(sea-doo)?Even if your compression rises?

[Joe St. Louis]

That depends on how much the compression has risen. Usually the compression doesn't rise that much just by boring but you should really do a compression check when the engine is back together. I don’t like to go over 185psi with 93 octane.

[Bill O'Neal]

Joe,
185 lbs pumping compression is quite high, especially on any large bore motor. It would take well over 14 to 1 compression ratio to reach that high of a pumping compression number on a large bore motor, and that would be destructive to a 951, for instance.
An example would be a smaller motor, such as a 550, could live with this high a number, but a 951 would self destruct in a very short period of time if much over 160 psi, and then it would need .060 or more squish clearances.

[DTH]

It's the 787 engine and I think it's bored one and a half.Cranking compression is around 160.

[Bill O'Neal]

DTH,
Use medimum grade or premimum grade fuel. Don't risk deto damage.

[DTH]

Thank You.