How much compression is safe on pump gas?
11-09-2012, 11:42 PM
#1
How much compression is safe on pump gas? I see guys on here running well over 10:1 with these engines which already well exceeds the numbers I'm used to running with the old technology engines. What is a safe ratio with these engines and pump gas?
Also is there a direct correlation between how much is milled off of the heads and the length of push rod you will need?
Also is there a direct correlation between how much is milled off of the heads and the length of push rod you will need?
11-10-2012, 12:00 AM
#2
That's a loaded question about the compression. It all depends on what you have your timing at and the octane of the pump gas. My 84 SS has 12.7to1 compression but I ran it at the strip on pump premium with the timing slowed to prevent detonation. As for push rods, always measure for the correct length. A length checker can be your best friend.
11-10-2012, 02:46 AM
#4
Really depends on the timing and the cam's intake valve closing point (IVC) after bottom dead center (ABDC)
Normally you want your dynamic CR around 8-8.5 max, 9-1 or more on race gas. I have a BBC in the works at the moment with 12.5, but the dynamic CR is 8.0:1.
Wallace racing has many calculators you can use to figure out your dynamic (involves valve events) and your static compression ratio. Keith Black has a calculator on their site as well.
Normally you want your dynamic CR around 8-8.5 max, 9-1 or more on race gas. I have a BBC in the works at the moment with 12.5, but the dynamic CR is 8.0:1.
Wallace racing has many calculators you can use to figure out your dynamic (involves valve events) and your static compression ratio. Keith Black has a calculator on their site as well.
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11-10-2012, 12:20 PM
#12
Hey Zone, Im running 11.4 static comp on my 406SBC with cast iron heads at 37 degrees of advance on timing. The real key,like others have said, is the cams duration and degree. I when one size up on the cam in the 406, just to bleed off some cylinder pressure so I would be safe with pumpgas. Works like a charm. What really suprised me was how responsive that motor is down low. I fully expected the engine to be a slug below 4k ,but it revs like a chainsaw from 2500 to 7100. Just throwing it out there. Good luck OP
11-10-2012, 01:46 PM
#14
Hey Zone, Im running 11.4 static comp on my 406SBC with cast iron heads at 37 degrees of advance on timing. The real key,like others have said, is the cams duration and degree. I when one size up on the cam in the 406, just to bleed off some cylinder pressure so I would be safe with pumpgas. Works like a charm. What really suprised me was how responsive that motor is down low. I fully expected the engine to be a slug below 4k ,but it revs like a chainsaw from 2500 to 7100. Just throwing it out there. Good luck OP
