11:1 piston worth it on 400ex

[glamiskid395]

im new here but not to atvs

from what i have been told on other forums that 400ex's have a compression ratio in the 9's, is this true?
if it is, would going to the 11:1 piston from JE or Wiseco be any better?

what would i gain?

heres whats on my 400ex as of now. K&N, no airbox lid, WB e-series pipe, largest main jet (165 i think).

thanks

[400exrider707]

Largest main jet? Not sure what that means!?

Anyways an 11:1 would be a nice upgrade, I suggest doing a cam at the same time, the two upgrades compliment each other nicely.

[Huzler]

or you could just buy my 05 440 11.1 stage 2 cam and is pretty quick

[glamiskid395]

the main jet in the carb is 165 i think, but i would have to check to make sure.

buying another bike is not an option...

[400exrider707]

Originally posted by glamiskid395
the main jet in the carb is 165 i think, but i would have to check to make sure.

buying another bike is not an option...

I'm just wondering why you said that is the "largest" main jet!? I dont know what you mean by that. That also still seems quite rich. What other jetting are you running? What pilot, where's the clip on the needle and how many turns on the fuel screw?

[glamiskid395]

the pilot is whatever came with the dynojet kit
the clip is the 3rd slot down.
fuel screw is at stock setting.

i dont think im running rich but if i am what is the easiest way to test that?

[Dr89]

take your spark plug out and look at it, if its black your running rich.

as far as the piston, if your going into the engine i'd go ahead and follow 400exrider's advice and get the cam too, the extra compression by itself wouldnt be great, at least to me it wouldnt be worth going into the engine for.

it also wouldn't be a bad idea to upgrade your cdi while your at it...that rev limiter is frustrating as hell on the 400ex's.

[glamiskid395]

thanks for your help guys.
i may not be doing this until the end of the glamis riding season.

[DAVE14]

Ive got an 11-1 Wiseco 440 with the hot cams stroker cam open box jetted & a pipe & its a vast improvement over stock or even a well modded 400 even if you do keep a 400 displacement the cam is a good compliment to the compression as well as a pipe jetting etc. but with raised compression dont cheap out on the cyl. head studs or youll be doin this job over & over $$$$

[400exrider707]

Originally posted by DAVE14
Ive got an 11-1 Wiseco 440 with the hot cams stroker cam open box jetted & a pipe & its a vast improvement over stock or even a well modded 400 even if you do keep a 400 displacement the cam is a good compliment to the compression as well as a pipe jetting etc. but with raised compression dont cheap out on the cyl. head studs or youll be doin this job over & over $$$$

Head studs are wasted money IMO on anything 11:1 and under. 12:1 and over and I would put them in for sure.