Compression

Just wanted to check something. What are typical compression ratios for competetive TAFC/TAD motors? Heard some numbers bantered about lately that sounded a lot higher than I would have expected.........

 

I think you'll find there's a fairly wide range of Comp ratios being run.
Some guys like to run 'em pretty high - 11.5:1 or maybe more.
The most common approach is probably in the 10:1 to 10.5:1 area, and there's probably some guys running down into the 9's.
It can all be made to work with the right tune up, but the higher ratios are less forgiving of any errors in fuel or timing. Lower ratios allow for more aggressive tune ups.

My thoughts... anyone else care to offer theirs.

 

Thanks. A guy around here was trying to tell me that some of the roots guys were up around 13:1. I just found that hard to believe.

 

all depends

depends on what you wanna do. I run between 11.5 to 12.5 to 1 for a mild bracket engine. 8.0 boat. If I was going to make some real power, I'd run 13 or so.
Sure it is sensitive to tuneup. Isn't everything that makes a ton of power?
9:1 is for competetive gas motors (well 8.5 or so).
I have an 8.0 boat, 468, 11.7 to 1 easy on parts. I adjust the valves every few race weekends whether I need to or not. Run 8000 through the traps.
Wags

 

Very sensitive question. Have to say boats are way more forgiving than a competitive TAFC/TAD. They just don't load the motor the same. The GPM is lower on a boat in my experience. The original question doesn't ask if it is a roots or a screw car. Remember a TAD is different than a TAFC with a screw. Different overdrive. Smaller cubes. More boost.
Final comment - less is better when learning. Sort of asking for trade secrets. Work with a professional tuner when starting out as there is more than one way to approach it. Cheaper in the long run.

 

The 13:1 sounds more like a Pro-Mod setup; because of the 20% over restriction they can up the compression. We have always run somewhere 11 to 12:1 in our AFC, and then you have to be real careful with the tune-up.

I agree with Dale get yourself a good tuner and work out your combination with him, it will save you thousands. One suggestion set your motor up with the maximum amount compression you and your tuner agree on, and then increase your head gasket thickness to drop your compression to where it will be easier to tune until you get things sorted out

 

Theres no secrets here,...Hello

we dont make enough money doing this racing
to be keeping secrets from one another
especially running in the NHRA.
share and share alike, scratch mine scratch yours.

Just had a opinion and shared it,...Now Merry Christmas.

 

I gotta agree. I don't race NHRA - but the concept is good.
I don't think comp. ratio will make someone a class winner, and there's too much of the "secret squirrel" stuff.
Sharing the info makes more fun for everyone...

BTW - don't assume that the higher ratio is the best ratio.