So the motor in my boat is a Harman Marine 405hp,454. As far as I know it's all original (1981) except intake and carb. Tag on the block says run 94 research octane, initial timing at 10 degrees. The heads are open chamber rectangle that I think are 118cc. I havn't had the heads off but by sticking a wire in a spark plug hole with the piston at the top the pistons seem to be flat top. I found an old spec sheet on the motor that says 8.75:1 compression and the flat top pistons seem to comfirm this.
My questions are: is my timing OK at 10 degrees initial and 35 total? And with that timing should I be OK with 91 octane pump gas?
Thanks
Gary