Screwcharged Compression Target

There seems to be a few schools of thought regarding what static compression to run in a serious screw compressed meth application (D or C). Obviously a lot of factors come into play, not the least of which are the cam/head designs.

What are some of the modern funny car and outlaw promod screw engines running these days for static compression? I've been given recommendations as low as 10:1 and as high as over 12:1. Is there a better dynamic measure to use?

Curious as to any thoughts or feedback.

Thanks.

 

(boost psi / 14.7) + 1) x motor compression = effective compression. Look for a number between 45 and 50.

 

comp

Also depends on the cylinder head your using as well.

 

Agreed, as a rough rule of thumb. However "Boost" is an arbitrary quantity and it is a function of a lot of variables.

To my way of thinking, the dynamic compression ratio (the trapping ratio which exists after IVC) would be of more relevance for tuning. Has anyone explored screw meth with in cylinder pressure sensing? That's the direction I am headed in, but would like to talk to others who may have already been there.

Thanks, and please PM if not wanting to discuss in public.

 

what happens if you exceed the recommended number of 50?

 

You lose performance because you have to run it too rich or too retarded to not hurt parts.

 

I would think that your cam timing would come into play here and we would have to take a look at the dynamic compression ratio. If you are running a cam with minimal overlap and are trying to trap as much into the chamber as possible, you would have a problem. If you were running a more aggressive cam with more overlap, less of that incoming high pressure charge will be trapped in the chamber because more of it is blowing out the exhaust. I would think that this would help to cool things down a bit to a manageable temp, but I don't know for sure, as I haven't tried it yet. It seems that is what the nitrous guys try to do with their high compression, large cams, but they don't run much for timing either. I would also be interested in hearing thoughts/data about cylinder pressure sensing.

 

There are an infinite number of theoretical possibilities.

 

And it depends on your budget!

 

so your saying the 45-50 is in the safe zone for ALL applications?

 

It was the answer to the original question.