compression testing

[terboed]

ok i tested the compression on my 98 shee. it read 120 left 135 right. do you have to hold the throttle wide open to get a more accurete number? i read this after i tested. are these decent numbers for stock? im about to install my noss head. what domes should i run for pump gas? i have 22, 21, and 20s.

[J.J.]

Originally Posted by terboed

ok i tested the compression on my 98 shee. it read 120 left 135 right. do you have to hold the throttle wide open to get a more accurete number? i read this after i tested. are these decent numbers for stock? im about to install my noss head. what domes should i run for pump gas? i have 22, 21, and 20s.

The individual numbers are good, however, as a pair they don't look too good, they differ with more than 10%, this could indicate a problem.
The test should be done cold, ignition off, fuel off, throttle wide open.
Kick until the pressure reaches max on the gauge.

Regarding your Q on the domes, if it was my decision, I would take a chance on the 20cc's and do a compression test to see where I'm at. If you end up in the 150PSI range you should be ok, anything higher and you should be thinking about race fuel...

[PA_Banshee]

My banshee came in around 135 each with very little difference between the cylinders. I've always heard what J.J. said about the difference between the 2.

My friend has 18's in a cool head on a banshee and it needs a mixture of race and 93 to get it to run good. The compression on his was a little over 160. I think I'd put the 21's in to be safe, but it will probably be fine with 20's.

[terboed]

alright i will try the 20's. might as well do a top end while im at it. thanks guys

[nickxc]

ok, I have heard that it is bad to have more than 10% difference between cylinders also but what will happen if you just run it. if they are both above 100lbs, like terboed has, what will happen if you just run it like that... just wondering... Thanks!!!

[PA_Banshee]

Nothing will happen right away. It's just an indicator of uneven wear between the 2 cylinders. It just lets you know that a rebuild is coming soon because your one cylinder is going to get some crappy compression.

[gixxer1kr]

If it were me i wo uld do the domes and get it running the best you can and when they get a little lower do a top end rebuild.Only reason being is so you can get a ballpark idea as to what mods did what as far as performance gains..Do the domes and youll be happy and a little way down the road do a top end...Ull be getter more power twice and be even happier LOL...But keep an eye on the comp on the 2 cyclinders....Just my 2 cents LOL!!!

[nickxc]

Ya I would do one and then the other too, unless you have the $$$ now and want to get it done.... its all your call i guess