Re: IML: Engine Compresson

[David Whitney <david.whitney@xxxxxxxxxxxx>]

Here is a good and relatively simple calculator.  You can go more in-depth
to the point where you're over your head, but I don't seen any reason to do
so based on your question.

http://www.rbracing-rsr.com/compstaticcalc.html

Your rebuilder should be able to give you all six numbers you need.  If
your pistons are flat-top (neither dished nor domed), then you only need
five numbers, and if your deck height is zero you only need four numbers.

A stock rebuild won't have much impact on the 10:1 ratio.  If you want to
have an impact on that figure, you must vary the piston dome shape (+ or
-), mill the head/block surfaces (+), modify the compression chambers (-)
or use other than original for your engine cylinder heads (+ or -).  A
small correction + or - can be made by varying the head gasket thickness.

At 10:1 you are already pushing the limits of modern pump gas.  Above that
you'll need special (= $$$) racing fuel.  There are special tips and tricks
that will allow you to run that kind of compression on regular pump gas,
but your rebuilder must be aware of them and incorporate them into the
rebuild so you can take advantage of them.  They mostly involve head
porting and timing adjustments that help control chamber temperature and
inhibit detonation.  There's a guy in San Diego who is quite the expert on
the topic, but he says it's not for the faint of heart.

Happy motoring,

David



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