P Offshore

I am curious if there is a formula to determine what octane rating is recommended for a particular compression ratio. I have a set of 12.5 : 1 motors I would like to run this year but have several different answers to the question what fuel.

hillbilly24

There is no set fromula it depends on alot of other stuff including timing, head design, and carb jetting to name a few. at 12.5:1 I would run atleast 100 octane and see how she handles it and go from there. Sunoco and VP both make alot of great fuels these days including some low lead stuff if you want to go that route. The best thing to do is talk to your engine builder and run what he recommends.

WETTE VETTE

I ran 13.2:1 compression in a solid roller aluminum head 496 for 5 seasons on 110 octane with no problems. I would not run unleaded or low lead fuel in that motor. Run 110 leaded and it will be fine. My .02!

Hydrocruiser

Timing advance and spark knock sensors and controllers also factor into this and the comp. ratio is not as important a factor if you are "hi-tech".

WETTE VETTE

Yes, a lot of factors apply, but if the motor is tuned for near maximum power output potential with 12.5:1 compression in a marine environment 110 octane is required. Running the carb fat, super cold plugs and retarded timing will allow you to run lower octane fuels, but at the expense of HP and driveability!

traviss

i run 12.7:1 in my small block.... 110 octane always.. better to be safe then sorry