std bore higher compression

[finsteratv]

has anyone put a std bore higher compression piston in there 400ex? if so what other engine mods did you run including exhaust? thanks

[rubbersdown]

lots of guys do. you can go up to 11:1 compression with a cam on premium pump gas. Any higher will need race fuel.

[EX400ANDREW]

add a hotcam while your in there and spend some time jetting the carb to get the 400 to rip

[finsteratv]

i do alot of trail riding/building but my dad has been talking about driving down watching the beginning of baja then going to glamis next year. just looking for more power in the future without boring. thanks for the info guys

[jensenracing77]

when the 400EX first came out i got a new one and put a 10:1 piston in it. everything else was stock including exhaust and jetting. i had it at Glamis and raced several guys that had new aftermarket exhaust systems and all differant brands. i beat them all going up Oldsmobile hill several times. they all said there bikes were stock other than exhaust and air filters. i did not tell them i had a differant piston. they were all mad that a (what they thought was) stock 400EX with stock exhaust was beating them but yes, just a piston will make a difference but is is always nicer to put a cam in at the same time.

[CJM]

^ Exactly. If you have the right work done you can make alot of power.

With the proper gearing, my stage 2 cam, mild P&P I did, exhaust, 11:1 piston and open airbox Im doing quite well racing even slightly modified 450r's. People dont want to believe it, thats cool but dragging them with the mods is down to the rider at that point-topend is where I catch them as lowend is usually not as good.

Even so, a 400ex with the right mods is no joke.

[jensenracing77]

Originally posted by CJM
[ a 400ex with the right mods is no joke. [/B]

X2 big time

[finsteratv]

i was thinking to put a 416 on once i blow up what i have but i think a 10.5-1 or an 11-1 wouldnt be to bad before that then.:devil: thanks for all the info

[CJM]

I would do 11:1. Have your cyl checked to make sure its in spec and then decided on the piston. This way if it isnt in spec you can do a bore job.

[finsteratv]

ive heard mixed things about 11:1 about race fuel being a must and more heat. my future goal is more power on pump gas while keeping the reliability the EX is known for. what fuel do you run for your set up? overheating? reliability?

[rubbersdown]

99% of guys on here run 11:1 on premium pump with no problems.

[CJM]

Originally posted by finsteratv
ive heard mixed things about 11:1 about race fuel being a must and more heat. my future goal is more power on pump gas while keeping the reliability the EX is known for. what fuel do you run for your set up? overheating? reliability?

No issues overheating at all if its jetted right. I do have a spal fan just incase but Im usually moving fast enough that it gets aircooled. I only use the fan when putting around.

I have no issues with detonation or ping and only run 93 octane.

[jensenracing77]

Originally posted by finsteratv
ive heard mixed things about 11:1 about race fuel being a must and more heat. my future goal is more power on pump gas while keeping the reliability the EX is known for. what fuel do you run for your set up? overheating? reliability?
this is an area that i have major experience with and don't entirely agree with others here. i highly recommend 10:1 on pump gas. not all 11:1 built engines will have a broblem but some do. the cam selection plays a big part in this. if you want to keep reliability without the slightest worry, stick to 10:1. you could use the XR head gasket and gain a little more without any problem.

[CJM]

Just to add some more info:

Im running cometic gaskets all the way around.