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FE Power Forums => FE Technical Forum => Topic started by: DEANs427 on July 19, 2011, 06:30:57 PM

Title: calculation of dynamic compression ratio
Post by: DEANs427 on July 19, 2011, 06:30:57 PM

when using any of the published calculators, the intake valve closing point ABDC is requested, is this at .050 or .020 or 0 ? none of the calculators specify this and it makes a BIG difference....

Title: Re: calculation of dynamic compression ratio
Post by: jayb on July 19, 2011, 09:59:26 PM

It is not at .050", it is usually from the advertised duration number.  For a solid cam sometimes they'll give you the duration at .020", to compensate for the lash adjustment.  In that case, use the .020" number.  For a hydraulic cam use the advertised number.

What the DCR calculation is trying to determine is the point at which the intake valve is actually shut, so that the cylinder starts building pressure rather than just pushing air out the intake valve.

Dean, I have an Excel spreadsheet that I've put together that goes through the whole calculation.  You are welcome to a copy of it if you want, or send me the specs on your engine and I'll run the calculation for you - Jay