Pump gas, compression, and boats....
 

OK, opinion time:

How high of a compression ratio do you think is safe for pump (91/93 octane) gas?

No knock sensor, so no safety there.

I'm leaning towards something such as: You need not plan building a boat engine that depends on 91 or higher unless you have your own fuel truck, and or never plan on traveling out of range of said fuel truck and or inland gas station. High compression boats, turbine boats..ect. ect...Having to plan your every move around the fuel guage and present location takes a HUGE! chunk out of the boating fun factor.

Depends on the engine, but with a Big Block Chevy, that would be about 9:1.

Michael

staying small block for this project, didnt want to mess with relocating exhaust and motor mounts and all that comes with it..

If you run a small block, with aluminum heads and keep the temp at 160 or below, a 10-1 compression ratio should be no problem.


Darrell.

If this is a N/A engine build. I have run as much as 11.5:1 on 91 octane with no problems. There are some key factors of course which go with keeping them alive. Aluminum heads , water temp through engine 125-140 , ignition timing, Water volume to engine, and fuel curve. If you want to be very conservative .....not knowing every detail of your set up....stay around 10.0:1

I'm running 9.75 compression 540's. Dyno pulls were made with 93 and 89. 93 was fine of course, 89 could be run comfortably up to 4,000 rpm's. Once approaching 5,000 the knock sensor starting going off. If I'm ever out of range of 93 octane pumps I just need to keep from hammering on the throttles and everything should be fine. This info came from Mark at Precision Marine in New Orleans.

No blowers, N/A for the win... :D

With 64cc heads (which I have not aquired yet) we would be pushing 11:1.... Now I am going to go with larger cc heads to keep the compression down. 10.6:1 pistons and they took .080 off the deck, also had to go .040 over. #8 cyl had a bad taper to it.

i have a 598 with 10:2:1 it runs fine with 93 but i have back the timing down about 2 degrees and that is a 30' boat

i have had no problems with my 454 with aluminum heads at 10.7:1 on 93 octane.