OB_SUPERTUNER
Registered
Earl...I agree with Johnnycheese...you are close and I am sure it is okay. I have experienced somethings that might prove to be
helpful to some of you street guys that I suspect most to all of the performance enthusiasts that race or help prepare bikes for racing have learned. I learned this over the years preparing bikes for the AMA/PROSTAR
600 SS class where we are literally splitting hairs much like Pro Stock. With the inception of the new sportbikes having their camchains on the end and pressed on cam sprockets, it has come to my attention while performing compression checks that there were vast differences from bike to bike. This prompted me to want to discover why so I ordered some service manuals. I was surprised to see that the OEM's have this huge spread of acceptable tolerances...much more than us "timers" are
accustomed to. For instance...a Hayabusa factory service manual indicates that the compression is acceptable when it falls between 171 to 228 with 128 pounds being the service limit!!! I have found the reason for this wide spread to be the fact that the pressed on cam sprockets have a widely acceptable range that they will still operate under. For the discerning rider or racer the low side is not acceptable as cylinder pressures are directly related to heat and thustly power output. I can only suspect that due to the fact that it is an assembly line environment that when an assembler is installing the cams or whatever the device...
it needs to fall between "this mark and that mark" perhaps and if that ends up being where there is considerable "overlap", it will result in the engine compression coming up on the low side of the spectrum. If they are done with real close timings and little to no overlap, then the pressure wil be higher in the cylinder and subsequently so will the compression. This is the reason why it becomes difficult to compare numbers on a dyno from bike to bike and evaluating things like pipes and other performance bolt on goodies. Degreeing the camshafts is the answer to this problem. Just some things I have noticed through the last few years and only a few years ago it was totally unacceptable for compression to vary that much. Earl, try doing it warm and see if it stabilizes and is more consistent from cylinder to cylinder for you. Good Luck. Freddie
helpful to some of you street guys that I suspect most to all of the performance enthusiasts that race or help prepare bikes for racing have learned. I learned this over the years preparing bikes for the AMA/PROSTAR
600 SS class where we are literally splitting hairs much like Pro Stock. With the inception of the new sportbikes having their camchains on the end and pressed on cam sprockets, it has come to my attention while performing compression checks that there were vast differences from bike to bike. This prompted me to want to discover why so I ordered some service manuals. I was surprised to see that the OEM's have this huge spread of acceptable tolerances...much more than us "timers" are
accustomed to. For instance...a Hayabusa factory service manual indicates that the compression is acceptable when it falls between 171 to 228 with 128 pounds being the service limit!!! I have found the reason for this wide spread to be the fact that the pressed on cam sprockets have a widely acceptable range that they will still operate under. For the discerning rider or racer the low side is not acceptable as cylinder pressures are directly related to heat and thustly power output. I can only suspect that due to the fact that it is an assembly line environment that when an assembler is installing the cams or whatever the device...
it needs to fall between "this mark and that mark" perhaps and if that ends up being where there is considerable "overlap", it will result in the engine compression coming up on the low side of the spectrum. If they are done with real close timings and little to no overlap, then the pressure wil be higher in the cylinder and subsequently so will the compression. This is the reason why it becomes difficult to compare numbers on a dyno from bike to bike and evaluating things like pipes and other performance bolt on goodies. Degreeing the camshafts is the answer to this problem. Just some things I have noticed through the last few years and only a few years ago it was totally unacceptable for compression to vary that much. Earl, try doing it warm and see if it stabilizes and is more consistent from cylinder to cylinder for you. Good Luck. Freddie
