I have decided that i'm going to go with the 426 piston and just bore the cylinder to fit. I just can't decide on the 10:1 or 11:1 piston. I know the 11:1 piston needs 100 octane, but what octane do need for the 10:1 piston? What kind of difference in power between the two? I was leaning towards the 11:1, but i don't want to have to run the 100 octane all the time.

 

The power is pretty close between the two and the 10 to 1 will run perfectly on 93 or the highest pump gas u can get.

 

well i will tell you if your gona do it you might as well go with 11 to 1. i was told to run nothing
under 104 so i found some 100 octane av gas the guy said that it would be fine, well i put it in
and i could not get it tuned in then to find out
you can't get a good reading off of high octane
so i put in 94 pump gas and got it dialed in
then put in the 100 av gas again and it ran like
crap, so i poured it out again and put 94 back in
and it runs like a raped ape

99 426ex 11 to1 compresion, 3 angle port job, web cam, wb rev box, k/n, dyno jet kit, 6 air box vents, ids-2 super trapp pipe, 14 tooth sproket,
and 94 octane = kick *** power

 

About yhe highest octane pump gas i can get around here is 92. Do you think i could go with the 11:1 piston and run the 92 octane with a good octane booster. Or should i just go with the 10:1 and do the same thing?

 

go to the trxoutlawz web sight and ask them
or look for air or clucth in this forum one of
them has 11 and half to 1 and runs 91

 

I suppose i depends on the cam you are using too. If you go with alot of duration, you are going to have more air shoved into your cylinders, right?

 

FYI, the stock DS650 comes with a 9.7:1 piston and Bombardier recommends 91 octane. The ron wood stage 2 kit for the DS650 comes with an 11:1 piston and they claim you can run on pump gas. Are you sure there isn't a place you can get 93 or 94 octane within a reasonable driving distance from the places you ride? If it were me, I would want to run the highest compression ratio possible.

 

I run the 11:1 but at 4500 ft. I use 91 Pump gas. I havn't had any problems. In responce to the comment about the bigger cam it bleeds off compression at the lower end and at speed you never get a full charge in. The compression you choose should also depend on what cam you use. The wilder the Cam the more bleedoff of compression.

99 426ex , Web Cam, FCR carb w/ twist, CT revlimiter, DMC exhaust, XCT's ,K&N, One kit, Renthal bars, DG nerfs, Armidillo Swingarm plate, 8 paddle Haulers

http://www.trxoutlawz.com/

 

I have a 10:1 Wiseco 85mm in my 400EX. I run 104 octane because it is readily available around here. I also have one less tooth on the counter sprocket. I did both these mods at the same time so I'm not sure which had the greatest affect but there is a big difference. Much more than when I installed a e-series silencer and K&N filter. Acceleration is much stronger now, it just rockets out of corners. The only down side is that the rev limiter kicks in much sooner. I am definitley going to buy a higher rev CDI.

I am using the stock cam, 160 main jet, 40 slow jet, 3-1/2 turns out on the air screw, and 14 discs on the silencer, at 800 to 1,200 ft elevation.

 

I noticed that Cometic and other gasket makers list the same head gasket for the XR400 and 400EX but I thought EX came with a thicker head gasket stock. So when everyone says they have 10:1 or 11:1 compression which head gasket are they using, the EX or the XR.....(or is there really a difference). I noticed that Weisco now lists an 11:1 piston (stock bore) so with a EX head gasket would you have 10.5:1 compression?