06 heads

[txtec10502]

i used s.e. cast 10.25s in my 06 dyna 95 build was running s.e.204s and i had 210 lbs front ,205 rear compression.how did i get this much comp,from stock heads and stock gaskets??? i am using a andrews 55h now it starts a lot easyer .how much comp, will the 55 take ???

[Mike]

You've discovered the reason we do not recommend the 10.25 pistons when used with the 203/204 cams, but do when used with the 211/251's. It's all about the intake closing event and matching the mehanical compression to the cam timing. Though we often run cranking pressures of 210, it is pushing the detonation envelope, (and starter as you've noted). Tuning is critical to prevent detonation and even then the motor may have to be detuned, reversing the investment in performance. The later closing (and duration) of the 211's allows use of more compression giving overall gains and cams such as these will actually run lazy if the comrpession is not increased to restore the cylinder pressure lost from the late intake close.

Corrected compression ratio's help decide how far we can push cam timing with a specifc mechanical compression and the 55's show 9.4 corrected with 10.5 mechanical and 9.2/10.3 which is good. The 204's show 9.7/10.3 which is very high. We like to see street motors using pump gas to around 9.4. Much over 9.5 gets into detonation issues, based on our experiance. So your 55's put you slightly on the conservative side which is OK.

[txtec10502]

i checked comp, with the 55s,it is 195 both cyls, i thought that with stock heads and gaskets it would be lower, check them with 2 defferrent snapon gauges . can you figure my comp, ratio with the ccp #s??

[Mike]

10.5 would be the max recommended for the 55's. Based on past experiance, the 195 cranking pressure sounds correct. The corrected pressure, as in my previous post, is 9.4 for the 10.5, 55 combination. We consider 9.4 to be pretty close to ideal for the majority of street applications.