Max compression ratio on 91 octane??

[74swingerlover]

What's the max compression ratio I can go with on 91 octane??

91 is generally the best number around my area. I might find 94 from time to time, but I want to be able to drive my car without pinging. I should also mention I live around 700 ft above sea level and in the canadian prairies, car is only driven in the summer on nice dry days, not too humid.

 

[the wall]

this depends on your cam i have run 11.2 without pinging with a large roller cam but to be safe in most cases 10. or so. its more of how much compression in pressure and i have run about 170 psi successfully on 91 octane

 

[swinger340]

can run 11:1 no problem w correct cam choice. You need to be more concerned with you dynamic compression not so much your static. Check out one of the dynamic compression charts and start crunching some #s. You want your dynamic comp. to be @ or below 8.5:1 w iron heads and 8.75:1 w aluminum heads to run fine on pump gas. http://www.wallaceracing.com/dynamic-cr.php

 

[72bluNblu]

With iron heads you're looking at around 10.5:1 for most applications. But as the wall pointed out, it really depends on your cam. A big cam will let you run more compression because the dynamic compression will be lower than the calculated static compression (because of the valve overlap). It also depends on the specifics of the build- type of piston, shape of the chamber, amount of quench etc. With aluminum heads you'd want around 11:1.

But, if you're building an engine with iron heads to always run on 91 and never ping, the safe bet is between 10 and 10.5:1.

 

[K.O. SWINGER]

there are many things to consider as said, also timing and ignition but I dont like riding the edge on this subject and would stay below 170psi to much to lose