Author Topic: Squish  (Read 2482 times)

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Offline Al Smith

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Re: Squish
« on: August 11, 2012, 08:05:12 am »
You won't change the port timing that much by lowering the cylinder .The degrees will remain the same as far as "blow down " between the opening of the exhaust and opening of the transfers .The intake will advance slightly and the exhaust will be retarded slightly .Probabley around three degrees which if anything will increase the torque but might slightly decrease the top end speed .

With the increased torque most likely it won't even be noticed .

FWIW most older Stihls set the exhaust port opening at around 98-100 degrees .If you wanted to you can raise it up slightly to maybe 96 degrees which will give you more blow down and slightly more RPM's .If you only raise the compression slightly I personally would not change the actual port timing numbers but might widen the ports slightly .

More info the older models used maybe 45-46 thou clearance or squish and the gasket is a flat 20 thou thick .If you use sealant that might account for 2 thou thereby reducing the clearance by around 18 thou more or less .

There's a certain formula that takes into account the port time open ratios depending on the bore size and RPM's .MacDizzy ,Bell ,and Gorden Jennings might be some help as I can't remember them exactly myself .

 

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