Does anyone know about compression, dosent seem like it.. .. .. .. .. .. .. ..

[EastWest]

Ok, I have postd this question twice with no answers.:confused: :(


I have a ported 250r motor that runs on 110.

When I got the motor it was pumping around 215 lbs with a custom stock head that was leaky.



I want to know what kind of compression #'s i will be looking at with a 15cc cool head?




thanks all!!

[daniel_250r]

there must be some way of doing the math

[lndy650]

full stroke is 17.6:1 CR= V1+V2 divided by V2. CR being compression ratio V1 being cylinder volume and V2 being combustion chamber volume. so
250+15/15 = 17.6

to get corrected comp. ratio i need your cylinder volume from the top of the exhaust port. where V1 changes from cylinder volume to cylinder volume from the top of the exhaust port. these calculations are easy once you do them a few times
as for cranking compression thats not really important the important things are your ratio and your squish

[lndy650]

quote from a book i have

Where CR is compression ratio

V1 is cylinder volume at exhaust closing

V2 is combustion chamber volume



Traditionally, compression ratios have been measured "full stroke". That is to say, V, would represent the combustion chamber volume plus piston displacement from bottom center to tog center. Thus, a combustion chamber volume of 28cc and a piston displacement of 250cc, calculated full-stroke, would be
250+28 divided by 28
CR= 9.93:1



But a far more realistic figure is obtained when V1 represents the cylinder volume above the upper edge of the exhaust port, and if we assume that our hypothetical engine has an exhaust port height equal to 45-percent of stroke, then V1 becomes 55-percent of piston displacement plus V2, and calculation goes like this:


(.55+250) +28 divided by 28
CR= 5.91:1

[EastWest]

I will get thoes numbers as soon as I get my trike moved..