Steven
11-28-2002, 02:43 PM
After all the good threads on quench area and how it pertains to compression ratio, I decided to verify the Wiseco falacy.
My 440 is equiped with the Wiseco 89mm piston which yields 435.48cc of displacement at BDC and is advertised to yield an 11:1 compression ratio.
After warming the bike to operating temp, I brought this piston to TDC and proceeded to fill the combustion chamber with motor oil via the spark plug hole.
After 51cc of motor oil was added to the combustion chamber, the oil level came to the first thread on the spark plug hole. Well, (435.5+51)/51=9.54:1 compression ratio. What an upset.
Now the plug hole on ther 400EX is angled, so oil will reach the lower side of the threads before it reaches upper. So I quit adding oil once it touched the lower thread.
I repeated the procedure after clearing the oil from the chamber and got the same results.
So I guess, I'm stuck with about a 9.5:1 compression ratio.
This sucks!
Two questions...
What is the margin of error determining C/R this way and am I better off getting a defferent piston or messing with decking and gasket thickness?
Thanks-Steve
My 440 is equiped with the Wiseco 89mm piston which yields 435.48cc of displacement at BDC and is advertised to yield an 11:1 compression ratio.
After warming the bike to operating temp, I brought this piston to TDC and proceeded to fill the combustion chamber with motor oil via the spark plug hole.
After 51cc of motor oil was added to the combustion chamber, the oil level came to the first thread on the spark plug hole. Well, (435.5+51)/51=9.54:1 compression ratio. What an upset.
Now the plug hole on ther 400EX is angled, so oil will reach the lower side of the threads before it reaches upper. So I quit adding oil once it touched the lower thread.
I repeated the procedure after clearing the oil from the chamber and got the same results.
So I guess, I'm stuck with about a 9.5:1 compression ratio.
This sucks!
Two questions...
What is the margin of error determining C/R this way and am I better off getting a defferent piston or messing with decking and gasket thickness?
Thanks-Steve