compression

[Toadz400]

what's the highest compression piston you can get for the 400ex without switching to race gas and just staying with 93 octane?

[speedy400]

11:1;) -darren

[wgbanks]

I have a JE 11:1 416 piston and a Hot Cam Stage 2 and I have to run race gas mix or I get detonation under a load after she warms up.

[Toadz400]

Originally posted by wgbanks
I have a JE 11:1 416 piston and a Hot Cam Stage 2 and I have to run race gas mix or I get detonation under a load after she warms up.

uh so anyone else have an opinion on this?

id stay around 10.8:1 then u wont have any probelms if ur out in the trails and u run outa gas.

[Toadz400]

Originally posted by 93 300ex
id stay around 10.8:1 then u wont have any probelms if ur out in the trails and u run outa gas.

uh...so what exactly are you saying?:huh

if i run out of gas, it'll keep running on air:blah:

[Toadz400]

Originally posted by wgbanks
I have a JE 11:1 416 piston and a Hot Cam Stage 2 and I have to run race gas mix or I get detonation under a load after she warms up.

okay i just noticed that you said 416, so if i have a 400 piston w/ 11:1 will i need to use race gas?

[honda250xrider]

with 11:1 compression i would at least run half and half, when you go over 11:1 compression i would run full race gas. i've heard that you need to run half and half in 10:5 compression also.

ok dude what i meant is if u are out in the woods and u run outta gas, u don't have to worry bout borrowin some of ur buddys gas but if u got a 11:1 it would run hot but the 10.8:1 is jsut a better choice in my opnion.

[Toadz400]

what is the stock compression on a 400ex? and what is the highest compression i can go without going up from premium.

since you guys were talking about mixing half-and-half with 10.8:1, and i don't really want to do that since it's still pretty expensive nowadays.

[cals400ex]

the stock compression is 9.1:1 on a stock 400ex. right now i am running a 10.8:1 with thinner gaskets so i around 11.1:1 and i am running on 93 octane. my bike runs just fine. i think you will be ok with 11 or lower.

[Toadz400]

Originally posted by cals400ex
the stock compression is 9.1:1 on a stock 400ex. right now i am running a 10.8:1 with thinner gaskets so i around 11.1:1 and i am running on 93 octane. my bike runs just fine. i think you will be ok with 11 or lower.

k, sweet, that's all i wanted to hear:D thanks a lot

this winter i'm taking apart the 400 and getting new of everything basically, bearings, seals, brakes, cables, and i was thinking of getting new rings, but decided why not get a piston too, and i wanted to get a higher compression for more power.

10.8 will run fine on premium but the 11:1 will run hot not the 10.8 so get the 10.8:1 compression stick with jd or ross pistons too.

[Out_Sider]

WISECO SUCKS!!!!!!!!!!!! trust me!!! :mad:

thats why i didn't reccomend it.

[RED121572]

Heres my theory.....

If you have race gas available to you, get a high compression piston, youll thank yourself.

My first project was a 11.1 406EX. It was ok. I could stay right with a stock Z400.

Now, the 435EX that I built is a whole new ball game. Its quite impressive.

Good luck on your rebuild!!:D

why can't a stock 400 keep up with a z???? the z has dohc thats bout it.

[r deorksen]

was wondering what concerns there are reguarding wiseco pistons. why should I stay away? what piston would be reccomended with stock bore and around 10.5 compression, any t thoughts on this would be great thanks

[nakomis0]

Originally posted by 93 300ex
why can't a stock 400 keep up with a z???? the z has dohc thats bout it.

One reason is stock comp. on a 400ex is 9:1, and stock comp. on a Z400 is 11:1.

You can go higher compression easier on a liquid cooled machine.

[wilkin250r]

Be careful. Just because someone says "I run a 11.5:1 compression and I can run pump gas just fine" doesn't always tell the whole story.

I have heard many things about Wiseco pistons not living up to their compression numbers, so someone "claiming" that they are running 11 compression may actually only be running 10.5, which WOULD run fine with pump gas.

[Toadz400]

which one is better for their money? JD or Ross? i've heard only crap about Wiseco's 4-stroke pistons so i know i'm not going with that. okay i have it figured out, this winter i'll get a 11:1 and probably run 1/4 race gas with 3/4 premium. does that sound good? and if you guys have a problem with it, fine, i'll just go with half and half....but gas here is starting to get pretty expensive, just premium is 1.74. and that's the CHEAPEST in the state pretty much.

the only bad thing bout that plan is that ive been told race gas doesn't last that long i think it had a 2 month date.

[Toadz400]

Originally posted by 93 300ex
the only bad thing bout that plan is that ive been told race gas doesn't last that long i think it had a 2 month date.

well i wouldn't be storing the stuff, and i go through gas a lot because i ride a lot....so it wouldn't last me 2 months. probably a month at the most.

[cals400ex]

it is actually a JE piston, not a JD. just clairified so you didn't get confused. the ross piston is a little lighter. what does this amount too? not much, you may feel a little better low end out of the JE and a little quicker reving engine out of the Ross. it is probally not noticable though. i am running the Ross and i haven't had any problems. my friend has the wiseco and he did not have any problems with it either. i wouldn't get one though. with a Ross 10.8:1 and thinner gaskets, my bike runs good with 92 octane as i previously stated. my bike runs the same with 92 vs 93 octane, but there is only a small difference between the two. i have not run race fuel through it before. you should be running fine with 1/4 race to 3/4 pump. good luck

[Toadz400]

Originally posted by cals400ex
it is actually a JE piston, not a JD. just clairified so you didn't get confused. the ross piston is a little lighter. what does this amount too? not much, you may feel a little better low end out of the JE and a little quicker reving engine out of the Ross. it is probally not noticable though. i am running the Ross and i haven't had any problems. my friend has the wiseco and he did not have any problems with it either. i wouldn't get one though. with a Ross 10.8:1 and thinner gaskets, my bike runs good with 92 octane as i previously stated. my bike runs the same with 92 vs 93 octane, but there is only a small difference between the two. i have not run race fuel through it before. you should be running fine with 1/4 race to 3/4 pump. good luck

yea i know it's JE. for some reason i wasn't thinking and put JD because i was reading what you wrote

i looked on JE and i couldn't find 400ex pistons, just crotchrocket pistons....so i'm looking on the Ross website right now. okay this blows, neither site has ATV pistons...what's up with this? where can i go that actually show you how much the pistons are and what's included, etc???

are there any other cheap engine mods that i could do to get some more power?

[cals400ex]

i would just call up c and d racing, the site sponsor. 308-696-7805 is the #. the piston comes with the oil ring, the top two rings, circlips etc. it comes with everything that you need. both pistons are the same price. i would put in a cam while your at it to help out on power.

[stupid driver]

Originally posted by 93 300ex
the only bad thing bout that plan is that ive been told race gas doesn't last that long i think it had a 2 month date.

I was told it can be stored upwards to 12 months. The guy said that if ya wanna be really safe, you can pour a little stabil in the gas can. He said that it will not hurt performance a bit. Got this all from the head guy at Sapp Bros. petroleum, so he knows his stuff

What gaskets are you guys using? Stock EX, or stock XR400 or another? Whats recommended? Also Isnt the compression listed for the dirtbike gaskets since your really just buying the XR piston from the bike. Will the EX gaskets lower compression a little? Thanks for the help.

Originally posted by QuadMX18
What gaskets are you guys using? Stock EX, or stock XR400 or another? Whats recommended? Also Isnt the compression listed for the dirtbike gaskets since your really just buying the XR piston from the bike. Will the EX gaskets lower compression a little? Thanks for the help.

i run OEM stock 400ex gaskets they are thicker and more durable...never had a problem with them...but i may switch to the stock xr 400 just because they are a thinner gasket giving you more compression...there are no recommendations...either u get OEM, XR 400, or cometic....either way make sure u get the steel...no the oem gaskets dont lower compression...that is the average size for thickness of gaskets so it would be whatever you bought...unless you bought a wiesco then u need to read the thread how to deck the cylinder or decking the cylinder...i bought 10.8:1 so with oem i am running 10.8:1 if you want to check out your EXACT compression go to www.rosspistons.com and check out there calculater for compression....and the best pistons are ross and JE...JE is tons more durable and a much finer piston then the ross but the ross piston is lighter...i went JE because my 416 revs out fast enough as it is

Originally posted by XxHonda_RacerxX
i run OEM stock 400ex gaskets they are thicker and more durable...but i may switch to the stock xr 400 just because they are a thinner gasket giving you more compression


Originally posted by XxHonda_RacerxX
...no the oem gaskets dont lower compression

Since the XR400 has thinner gaskets it has a higher compression then the EX ones because the EX are thicker so the EX WOULD lower compression right? Is the compression listed with XR or EX gaskets. Thats my question. I think that it is with XR400 gaskets but i just want to make sure. Also what are the 400EX and XR400 gaskets made of? Thanks for answering.

[cals400ex]

i think he was saying that the oem ex gaskets won't lower compression but the oem xr gasket will lower the compression. i have been told don't get the paper gaskets since the steel are of much better quality.

ok...let me re word this...Steel is way better then composite...get steel...oem is steel...the oem ex gaskets are what the pistons are tested on...the oem xr gaskets are thinner then the ex gaskets so your compression would go up...say u ran 10.8:1 like i do...and u bought oem xr gaskets...you would prolly go up to around 11:1 or 11.1:1

Originally posted by XxHonda_RacerxX
ok...let me re word this...Steel is way better then composite...get steel...oem is steel...the oem ex gaskets are what the pistons are tested on...the oem xr gaskets are thinner then the ex gaskets so your compression would go up...say u ran 10.8:1 like i do...and u bought oem xr gaskets...you would prolly go up to around 11:1 or 11.1:1

thanks. that cleared it up :D