[duc dude]

I installed some 11:1 je piston wondering what a normal compression reading so be with stock heads and cams 91 900ss

 

[dirkwrong]

I installed some 11:1 je piston wondering what a normal compression reading so be with stock heads and cams 91 900ss

It should be between 17 and 20 times the compression ratio. In your case, between 187 and 220 psi. This is after the rings wear in, of course. I don't think that takes very long though. I do not know if the cams in these engine effect the test, but according to what I have read, a more radical cam can reduce the reading by 10 psi or so. This is only at cranking speed, obviously.

 

[1fast750ss]

It should be between 17 and 20 times the compression ratio. In your case, between 187 and 220 psi. This is after the rings wear in, of course. I don't think that takes very long though. I do not know if the cams in these engine effect the test, but according to what I have read, a more radical cam can reduce the reading by 10 psi or so. This is only at cranking speed, obviously.

Also to consider is the cam timing as it will alter running compression by advancing it.

 

[duc dude]

yes the cam timing will effect the pressure I've looked for some kind of center line spec. but no luck does any know what the stock center line spec. is or good one would be for a 91 900ss

 

[ENGAKATS]

Maybe this site is usefull for you: http://www.bikeboy.org/performance.html#2v

 

[CJS]

There more than 11.1

Run whatever centerline gives you a closing figure of 68-70degrees intake closing or the dynamic compression will give you some ping/detonation.



In other words run standard valve timing . Brad has valve timings on his site . www.bikeboy.org.


run standard ignition timing too. You can run the hotter advanced cam timing but you wil get detonation unless the pistons are machined . there is not any difference in the hotter cam set up with machined pistons vs non machined pistons and standard valve timings.