Compression ratios

[yammirider]

hey, I was looking at some 85mm JE big bore kits on ebay and really want to go with the 12:1 but am worried about getting pre-ignition or pinging with running it off 93 octane pump gas. I have heard stories of people doing it on this forum. I was doing some research and found that one of the reasons you could do it is because in some heads there aren't any hot spots or sharp edges that could heat up enough to pre-ignite with the higher temps of having higher compression. I also read that large lift and duration cams tend to bleed off just a little compression.
For my build I was planning on doing 12:1 JE with Kibblewhite valve springs and a Web .450 (or .430 haven't decided yet, been reading around the forum though).

what do you guys have to say about running 12:1? prefferably the ones that are running it. Any input is great really

Thanks

 

[yamarider]

You might be able to run it on 93 but it's going to run a lot hotter than a 11:1 or with higher octane. Not normally a problem but these things are air cooled and even stock can get pretty hot at times if there's not a lot of air moving over them like riding in slow, technical trails or in a group of slower riders.

 

[DeadLastRacing]

I run JE 11:1, .40 bore, .430cam and kibble HD springs. If I could do it over again I think Id go with the .390 cam. Oil cooler mod is almost a must when goin like this or higher with the engine.

 

[yammirider]

Yeah I already have the big bear setup. Where did you get an 11:1 JE deadlast? is that a custom? I can only find 12:1 and 10.5:1. Also, where did you get your cam from? the 390 take s away some from the higher rpm power and gives to the lower compared to the 430 right?
thanks for the quick replies guys

 

[DeadLastRacing]

My piston is an older model (I got it off of Dave76) but back in the day, JE did offer 11:1, if your lucky you might be able to find one that has been sitting on someones shelf. Its an 85mm piston but at one time got milled down to 84.5(?) and it was a bitch to find the rings to fit that size, luckily I did. The .430 cam is from Poweroll (I also got that off Dave76)

Yes the .390 gives you some of the lower end power (faster revs) that the .430 is lacking. Something that I would like to have back because I tend to do more woods riding.

 

[yammirider]

god damnit! LOL dave where do you get your stuff lol where can I order poweroll cams?
deadlast I saw your quad on youtube I think, the guy that hit the tracks at 60 mph? weh, that frame got bent

 

[DeadLastRacing]

Yupp, thats my quad rebuild in picture form on the youtubes!! Hahah. Poweroll has a website http://www.powroll.com/P_YAMAHA_WARRIOR350.htm

Also check out hotcams and webcams (webcams before hotcams is my opinion)

 

[yammirider]

no I want to avoid hotcams at all cost. Heard so many stories of them breaking in half. They don't even require HD springs. Looking to avoid valve float. And thanks, I was looking everywhere for their website!