How small a dome on a new stock motor?

[mplecha]

I've got a stock shee (with fmf fattys) that I want to put aluminum heads on and bump the compression a bit. How small can I go and still use pump gas? I can't check the compression now, because I'm out to sea. Assuming it was barely ridden (as it has been) what would you guys suggest?

[sredish]

The typical guideline is not to go over 155 with 92 octane or super unleaded. If you advanced your timing, subtract that number from the compression number for your max lbs. with super unleaded.

 

For instance:

 

Stock timing with 92 octane, I wouldn't go over 155 max.

 

+5 degrees timing with 92 octane, I wouldn't go over 150.

 

At sea level, 21cc will probably be fine, 20cc might put you over 160, and this I'm figuring this for sea level like you said. If a person was at 4,000 feet, then it'd probably take a 17cc dome to get them up to 150.

 

This is my opinion. Some will probably say that 160 is fine with super, and you could probably run 160 and not have problems, but if you become a little lean or overheat, you'll be more likely to detonate with 160 than with slightly less compression on super. I wouldn't take the chance.

[dlnoss]

Pretty much what sredish said. 21cc would be good at close to sea level with premium pump gas.