Compression - Pump Gas

[Mike Allred]

I'm thinking about running pump gas, am not sure of my static compression ratio, but have checked my cranking compression with butterflies open at 175PSI - warm motor. The motor is a 406 with flattops, 38 degree locked timing, World Products 200cc heads, .550/.572 254/260 @.050 flat tappet turning 6000 rpm. Do you guys think I'll be safe with 93 octane on this motor?

I do have the stock tank full of 110 Torco and could begin weaning the motor off of the expensive stuff a few gallons at a time. I top-off before every race...

 

[smitty84monte]

whats the cc on the heads?

 

[Mike Allred]

I wish I knew. I bought motor from a friend that thought they were 72cc...

 

[Damon]

Flattops and 72 cc heads on a 400 would be in the low 10s for compression, at the bare minimum. 175 PSI cranking compression with that big a cam tells me it's probably in the mid 10s at least. Long story short- dicey, but not outside the realm of possibility for pump gas. I'd pull that timing back to about 32* to do some "get acquainted" runs. Then bump it back up a degree or two at a time, being very attentive to your ET, MPH and any signs of detonation on the plugs (aluminum specks). In some cases pump gas burns faster than race fuel and might not even require as much timing to make optimum power. Might also require slightly different jetting. Just be careful and go slow with your tuning changes.