Another octane q?
 

Just wondering what octane should I be running? SB Chevys 9:0:1 compression

Probably 89 octane as long as timing is less than 34 degrees.

What does timing have to do w/it?

I am running 9.9:1 on my SBC with 34 degrees timing and run mid grade which is 89 octane, no problems at all...

Travis

Timing has everything to do with detonation and the need for higher octane gas. More timing and lower octane increase the risk of detonation. Detonation=BOOM!!!!

this may be obvious , sorry,
but higher octane in and of itself does not add power. higher octane burns SLOWER. BUT.......this allows you to add compression ratio, and advance timing before detonation (ie. predetonation before spark (like a diesel) or too far before TDC) in order to get additional power. Alcohol has a very high equivelent octane and therefore racers can run significant timing advance and compression running on alcohol...... for example.

We had a engine experiment station in college that allowed the head to crank center to be adjusted real time while the engine was running(therefore changing the compression ratio). torque/ Hp/ pressure in cylinder were all studied. various octane fuels were tested to show the effect / counter effect of compression ratio and fuel octane.

before the class, all of us 80's highschool motor heads were pissing away every $$$ we had into racing fuel for our stock camaros, till we learned about the true funtion of octane.

boat motors run different head and block temps that vehicles so your question about octane is a good question for this boating forum. sorry I don't have the knowledge to tell you if 89 is appropriate or not, but don't spend $$$$on 92 or racing fuel if you don't need to.

When we ran my engine on the dyno last spring after a fresh upgrading, we did the initial cam break in and several power pulls on the gas that was already in the dyno's barrells. It was racing fuel for a Busch Grand National Engine. Since the engine was only getting about 2 more horspower at 36 degrees total advance as compared the 34 degrees, we locked it in on the 34 degrees for the sake of being conservative. Then we switched to 89 octane fuel that I brought with me. We actually got about 5 more HP with the 89. I am running between 8.5 and 9.0: 1 compression. More octane is not always required.