ahh I worked it out
Craig Overend, if you change the " - TDC " in the chamber cc part of your formula to " + TDC " it's more accurate
 
if you use " - TDC " then as you decrease the distance from the piston to deck when the pistons at TDC the compression ratio decreases too, if you use " + TDC " then the compression ratio increases as it should
 
Dave
----- Original Message -----
Sent: Friday, June 28, 2002 5:44 AM
Subject: Compression Ratio's Yet Again

Guys I'm having trouble getting my brain around something to do with calculating compression ratio's.
 
I know the formula I'm using is correct, I've tried using figures for motors I allready know the compression ratio of and it's been spot on every time.
 
the thing that's got me stumped is if you increase the piston height value, the final compression ratio decreases.  I'm having trouble understanding how that works, shouldn't it increase compression since it's bringing the piston closer to deck?
 
I've tried using 2 compression ratio calculators as well, and exactly the same thing happens. The compression ratio calculator doesn't have a "piston height" option, but it does have "piston below deck" field, and if you bring the piston closer to the deck then exactly the same thing happens....compression ratio DECREASES
 
this has got me stumped :(
maybe I should stop trying using mathematical formulae at ungodly hours of the morning :) hehe
 
Dave

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