i got a 99 400ex and i'm lookin at putting a high compression piston in my quad. my question is this, what compression do you guys prefer and what are the diferences between the 10:1 and the 11:1 (besides the obvious). would i have to use race gas in either one of them or both. and what kind of power gains will i experience with that mod. also what else would i need to do to the motor....thanx for any help

 

I'd like to know the same thing. I'd like increased performance, but I don't want to run race gas. Thanks.

 

Red...

What is the elevation you are running the quad at?
I run a 11:1 in mine with no problem, but I am at 5000' elevation. I am going to a 12:1 JE Coated piston this week, and I am still able to run pump gas... I will have to use a mix of race fuel if I go to sea level..

My suggestion to you while you have the cylinder off is to add a 450/451 grind cam from webcam. Run an aftermarket exhaust system and a K&N air filter. Re jet carb as necessary. Do some mild porting, (clean up the casting marks and match port your intake with the boot, at least..) If you really have the cash, add a 39mm FCR Carb. If you do all of this you will find you will need the modified cdi box..

This set up will show a great improvement over stock... You will be happy with it. I know I am..

 

thanx clutch i ride at about 3200 ft and i do have a big gun pipe with a k/n and dynojet kit so i will look into the JE piston what makes you go with JE and not wiseco.....thanx for all the help man

 

Red,

I have found that the JE pistons are held to a tighter tolerance during manufacturing. Don't really know for sure if it makes any difference for us recreational riders. I currently have a weisco piston in and I just found out that JE doesnt make a 12:1 for the 400ex.. I am looking to go to the 12:1 for a bit more compression because I will be porting out the head and at my elevation that I ride (5000' and UP..) I will be ok. I may very well be using another weisco piston for this application.

Let us know how you decide and how your improvements work out...
Later....

 

Trxoutlawz Gt proformance makes a 12:1 piston for the 400ex I saw it in an old issue of 4 wheel action in the back it looked sweet. Did'nt know if you wanted to go with a different brand but just thought I would through it out there for you to consider. I think it was $225.00 but give them a call.

 

The Piston is a 12.5:1 and is sold by GT Thunder. I am pretty sure that it is a JE piece. Check it out at www.gthunder.com. Later

 

Thanks,

I will look into your suggestions. Thanks again for your help......

I am still in the research mode, unsure as to what setup I will choose...