What is my compression ratio?

[jesseweaver]

when i bought my 400 a couple months ago, the guy said it had a high comp. piston, but didnt say what the compression ratio was. i know if you have a higher compression, you should run higher octane gas. so is there an easy way to find out the compression, because right now im just running the higher octane gas. if i dont know, should i use racing gas? i can get this at the local honda dealer cant i? oh yea, if it helps, the piston is a Wiseco.

[cals400ex]

there is no real way of knowing without pulling the piston out. i would assume it would be there 11:1 model but that is a total guess, obviously. i know wiseco used to be known for having much lower compression than what they stated in 400ex's. i am not telling you to run 93 octane pump gas but if it was their 11:1 model i doubt you would have any issues with pump gas with your hotcam in place and proper jetting.

[jesseweaver]

i was just looking back at some old posts by him, and i saw it is an 11:1. but i never knew that the type of cam would affect the octane gas you use.

I just came to the conclusion again that maybe the owner before me put in a high compression piston. The reason i say that is 1 time on accident I ran 87 octane and my 400ex bogged down and ran like crap. I used it all up quick then put 93 and it was fine

[cals400ex]

yes, the cam does make a difference with what gas you need. the larger overlap on the cams helps to keep things cool