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Mod-O-Matic (beta!): Please vote with care. You must be logged in to use Mod-O-Matic Move post to: For Sale | Group Buy | Off Topic | NWS/Adult    Remove due to Spam/Troll | Prohibited       Highlight as: Informative | Success Story
 
Author:  
John in DC on 2005-04-19 at 23:35:56(Roadfly member #8387; Roadfly Inner Circle member since 2003-06-05) 
    
Subject:  
A bit of math to guide you... (627 views) 
Message: Here's an oversimplified formula for Effective Compression Ratio (ECR)...

ECR= [(atmos pressure+boost)/(atmos pressure)]*mechanical CR

Example A: 9:1 @10psi

ECR = [(14.5+10)/(14.5)]*9.0
= [24.5/14.5]*9.0
= 15.21


Example B: 8:1 @18psi

ECR = [(14.5+18)/(14.5)]*8
= [32.5/14.5]*8
= 17.93

Thus, it can be loosely said that with all other things being equal, car "B" would make more power since it will have higher combustion chamber pressures.

Of course, a more complete formula for ECR (one that takes head, piston, squish, and other volumes into account) will yield better results. Perhaps others will chime in on this.

Rgds...

- John
'92 850i Twin Turbo		 
 

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