Compression ratios for alky-fuel

Just curious what the range is for compression ratio for A; NA alky, B; Blown alky, C; NA fuel, and D; Blown fuel. Is there a difference in compression with percentage?

Mine is NA alky at 12;1 which seems to be low by what Im reading about others.

 

The NA alky I've helped with is 16:1, it's for pulling.

 

From my few years in Alcohol racing, 14'ish is about premo for injected, i have heard many times that 12 is about as high as you want (for a decent tuning window/parts longevity) for a blown alky deal.

Fuel? Not sure.

 

For alcohol, it depends on how much boost you make. For a really good roots blower or a screw blower that makes 50 pound boost, 12 to 1 would be way too high. For this application, the compression ranges between 10.8 to 1 and 11.4 or so. 12 to 1 would probably work ok with 20 or 30 pounds boost, but the tuning window is still fairly small.

 

I think it depends on the combustion chamber shape also; conventional chevy, hemi, 12° chevy, etc.

 

When my motor was NA injected we ran it at 14.5 to 1 and it ran pretty well. We also run an SBC in a FED at 13.0 to 1, I want to give it some more to see what it does, I have heard about 17 and 18 to 1 Small block chevy's, and they are all about a second faster than ours. There are some Jr/Fuel cars (NA Alky Small Chevy under 420") that run in the 6's at 200+, I dont know how they do it.

Now that the Big Chrysler is blown we run 11.5 to 1 but im only running 15psi boost......for now.

About the NA fuel, it all depends on the mix you want to run, at my 14.5 to 1 I made 4 passes with 20% just to see what happened, It was fun and i didnt break anything but 20% was a little too much for my CR I think. From what i hear if you want to run 80% to 100% dont run any more then 10.0 to 1 CR and the blown fuel motors are around the 5.5 or 7 to 1 CR, and that all depends on what kind of boost you throw at it, and your percentage of nitro......

 

The current car has Brodix B1s.

 

Jim,

You are talking NA right?

EDB

 

For now...

Ive got 2 400s and 2 440s waiting to be used. No telling what direction Ill go.

Im really NOT planning on blown nitro, just curious.