How much comp is to much

[Maul]

How much comp can I safely run with pump gas say 91-92 octane. I'm looking at a cool head with 18cc domes but I think it will give me to much comp at sea level

 

Bike has stock crank but is .80 over

[blanco25]

145-50

[blanco25]

145-50

in a perfect world those domes should get you at least 184-195 compression. this is one a fresh rebuild. best thing to do is get a good compreesion tester and go from there. better to be safe than sorry. call the guy in my sig. he knows a few things.

[AKheathen]

that is too much. 20 is the limit on 90, and i've heard people pushing 19's on 93 with stock timing. i would do 21's or 20's and +4 timing.

~160psi on stock port :thumbsup:

[Maul]

so it sounds like I could get by with 20's on stock porting and timing or should I just be on the safe side and go with 21's. Just trying to stay with 91 octane if I can. Would hate to buy some domes just to find out I have to much comp and have to run 100 or higher

[RILS]

so it sounds like I could get by with 20's on stock porting and timing or should I just be on the safe side and go with 21's. Just trying to stay with 91 octane if I can. Would hate to buy some domes just to find out I have to much comp and have to run 100 or higher

 

 

I would say 22s I have had 18s on mine with sevral sets of jugs and it always pulls 185-190 depending on which jugs.

[Maul]

so if I want to stay with pump gas would I better off just shaving my stock head .10 or .20 and not wasting money on a cool head. Would I only be gaining the cooling capacity of the cool head and not any hp.

[blanco25]

in vegas with kevins stock cylinders he ported for me i was at 187. with 17cc. my elevation was above 2000ft. check out nossmachine.com . what kind of coolhead is it?

[AKheathen]

no. i am running 20's on 90 octane without detonation, and have some 18's if i want to run higher octane temporarily and switch back to 20's. stock timing and porting

[Maul]

in vegas with kevins stock cylinders he ported for me i was at 187. with 17cc. my elevation was above 2000ft. check out nossmachine.com . what kind of coolhead is it?

 

Pro Design

[sheerider1026]

i am at 600 ft.. i run 93 pump gas with 19c domes and +5.5 on the timing.. it has a trail/cleanup port.. i am at around 165 psi.. tuning is a bit tricky

[RILS]

so if I want to stay with pump gas would I better off just shaving my stock head .10 or .20 and not wasting money on a cool head. Would I only be gaining the cooling capacity of the cool head and not any hp.

 

I cant remember what the stockers are but I wouldnt run it over 145 on pump gas and u can get that by shaving the head.I have some 18s I think im going to switch out myself. I havent been to this fourm in years and havent even cranked my banshee in a year. You should be around 120-125 with the stockers on there. I used to know how much to shave them but I dont remember now. Im running 4mil storoker but the compression didnt change with that it was the same with the stk. crank 65mm cubs 18ccdomes on a noss head@800ft 185psi on the cubs and 190 on drag ported stkers. 34pjs with trinty stainless pipes.

Edited June 27, 2009 by RILS

[blanco25]

bump up the timing a little, and get domes that will get you around 145-155 compression

[blanco25]

you should make a signature for yourself with all your mods that are done to your bike, and you'll get more accurate answers for questions that you'll be asking from here on out. just keep her updated :biggrin:

[Maul]

you should make a signature for yourself with all your mods that are done to your bike, and you'll get more accurate answers for questions that you'll be asking from here on out. just keep her updated :biggrin:

 

There hope that helps. Looking to put a head on the 87.

 

Also thanks for all the info guys. I have lurked around here for awhile but finally started doing a few more mods and this place has been a gold mine of info.