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Posted

I just bought a pro design cool head and was planning on getting a different set of domes since it came with 15cc domes and I really don't want that high of compression since I usually just trial ride and don't want to have to buy race gas. Question is I'm bored at .30 over, stock head now running 120psi comp. on both cylinders, boysen power reeds, and stock size carbs, with fmf pipe. Other than that I'm pretty much stock. When I buy a new set of domes do they have to be sized to fit my boring or will all of them work with standard bores of the engine? By that I mean not a big bore kit, but just standard boring up to 100 over. Also what size domes would you guys recomend. I wanna stay under the 160-65 range so I can run pump gas, as well as not put too much pressure on the rest of the engine since its not a new one being a 91 model. All replies are app.

Posted

the domes fit on top of the cyl. take ur current domes and set them on top like i said. thats what ur new ones will fit

Posted

I'm running 22cc domes with a .40 over bore and it runs like mad!! I think anything under 21cc your suppossed to run the good stuff . We do alot of trail ridding and all that , all I run is 93 octain and like I said it runs great ! you'll love it !! :cheers:

Posted

22cc is equivellent to stock, you can get away with pump gas down to 19's

If you wanna stay on the safe side run 20's and advance your timing 4 deg. w/ a light flywheel it makes for a really nice trail setup.

The domes don't come to suit differant bores, the piston is altered to correct the compression ratio.

.030 is like 2 fingernails thick, so it dosn't have much affect on the sealing surface of the head.

Posted
22cc is equivellent to stock, you can get away with pump gas down to 19's

If you wanna stay on the safe side run 20's and advance your timing 4 deg. w/ a light flywheel it makes for a really nice trail setup.

The domes don't come to suit differant bores, the piston is altered to correct the compression ratio.

.030 is like 2 fingernails thick, so it dosn't have much affect on the sealing surface of the head.

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depends on attlitude, with 19cc domes my cylinder psi is 185, thats to high for pump gas or even 50/50 mix. go to dlnoss web site. he has a chart that will get you in the ball park.
Posted

Based on your compression with the stock head, 21cc domes would be a safe bet with premium pump gas. What is the elevation you will be riding at? I'm not sure about other manufacturers but my 'standard' domes will accomodate up to .080 over.

Posted

Same with me... I use 19cc domes and I'm running 183 and I cant use pump gas

 

If you want to use pump gas 21 or 22cc domes will work fine

 

even with 22cc domes you will see a increase in compression

 

should be around 145psi with 22cc at sea lvl according to the chart (with a fresh top end) could be lower with top end wear

 

21cc 157psi

20cc 169psi

 

 

got my numbers from Pro-designs website

Posted (edited)

Thanks everyone. It really helps to have some advise from people that have used the equip. before. I think I'm going to try the 21's first and then I'll step up later if need be, after some work on the bottom end to make sure it'll hold up to the squeeze of more power.

Edited by PRAIRIEOUTLAW
Posted

One more quick question. Will the stock studs be long enough to mount the pro design unit or do I have to replace with longer ones? If so whats the best place to get them from. I haven't seen any on ebay or on any of the sites I've been searching. Thanks.

Posted

i run 20cc domes on pump gas with a stock bore and i was running 140psi and that worked super good so if i was you i would go with 20s. if you bore you cylinders out you dont have to do anyhting to the head all the domes will fit unless you have a big bore kit or something like that.

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