one is if i go with a high compression piston do i need to put a better cam in ?& have it port & polished .what should i go with ,i dont want to run race gas ,i just want a little more uuumph!its a trail bike ,but iam definatly going to try the sand dunes next year.

some one was sayong something about trimming something on the airbox that really helped out?

has anyone tried the ct slip on?thanks!

 

Come on guys I KNOW someone knows the answer to his questions lets help him.

 

Well as far as the piston yes it will help the bottom end, it will help even more with a cam and a flow port job. but you do not have to do but it is a good idea to do it in the future when you have the money. As far as race gas it depends on the compression on piston you get and hat altitude you are at. You can usually get away with running good pump gas with a 10:1 piston if you need anything else let me know I have two highly modded 400exs and work on alot of them each week

 

Supposedly you are ok to go up to 11:1 compression,I was leary and chose 10:5 and run 93 octane just fine.I would recommend also doing the cam at the same time rather than tearing it down twice unless you're doing the work yourself then doing the cam is easy enough to do later if $ is the issue.As far as the porting goes...sure it will help but this engine has relatively large and "clean" ports .I had my head ported when I ordered my cam so I can't tell you the difference it made to one that wasn't with the same mods. Many have used the XR 400 cam with good results especially for the $.I went with the GT Thunder and am pleased with the overall "range" in which the engine makes power,I don't even know if it's still available because I heard they burnt down.I have plenty enough low end that it makes it hard to keep the front end down in the tight trails,The damn thing makes alot more power than it did when she rolled off the showroom floor.If I was to do it again I still would be torn on using either of the two cams but would also like to try the xr cam to see the difference.If Gabe is watching maybe he can give you very good insight on these matters he is the Atv genius around here as far as I'm concerned. I hope that I helped.Jim