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250X_project
11-07-2006, 07:52 PM
what compression piston should I get with a stroker crank to be considered? 250X with a +12.7Stroker kit.
2004exrider
11-09-2006, 08:19 PM
I hope you like math:eek: (this is no joke either)

Ready...

Compression Ratio = cylinder volume + deck height volume + head gasket volume + combustion chamber volume DIVIDED BY deck hight volume + head gasket volume + combustion chamber volume

Jimmy
250X_project
11-09-2006, 08:26 PM
Now are there any parenthesis in there for the hole PEMDAS thing?
250X_project
11-09-2006, 08:28 PM
Now are there any parenthesis in there for the hole PEMDAS thing? How do I find out all this info? All I want to know is what compression piston will give me 11:1, after my longer stroke is taken into consideration....I was thinking 10.5:1?
underpowered
11-10-2006, 05:00 AM
Originally posted by 250X_project
Now are there any parenthesis in there for the hole PEMDAS thing? How do I find out all this info? All I want to know is what compression piston will give me 11:1, after my longer stroke is taken into consideration....I was thinking 10.5:1?

you compression will increase. your piston is going lower in the cylinder and going higher at TDC, so you are starting off with more air and compressing it into a smaller space.
bwamos
11-10-2006, 08:24 AM
As a ballpark figure.. not going into excessive calculations.. using an 11:1 static compression piston for a stock stroke in a +12.7mm stroked 250x will give you approximatly 13.4:1 static compression +/-.

Very basic calcs.. not accounting for head volume, dymanic compression, etc... just the basics for a very ballpark figure.

Stock 250x = 74mm bore x 57.3mm stroke.
246.3 cm^3
Compressed 11:1 = 22.4 cm^3

New stroke @ +12.7mm
74mm bore x 70mm stroke = 300.9 cm^3
Compressing down to 22.4 cm^3
300.9 cm^3 / 22.4 cm^3 = 13.4:1 ratio.

Loose math.. and very ballpark.. but get's you into the neighborhood. Actuall compression will be lower.. probably closer to 13:1 static. Dynamic.. has too many variables to calculate.
250X_project
11-10-2006, 02:27 PM
Your the man! :D Now not to be a pain but how would I get about 11 or 12 WITH the stroke figured in? Thank you!
250X_project
11-10-2006, 02:30 PM
Sorry forgot to mention my bore is not stock, it is an 86mm. :devil: Thanks!