LDJ,

I want to get as much as I can without running race gas. Do you run race gas with your piston? Which mods would you suggest to me?

 

With my piston only 92 octane is needed. If I were you I would start with a mild piston, I think you could go up to a 10:8:1 piston and still run pump. Then get a cam, but not a full race one, there are many companies who sell them but, I think they are all similar to the web cam 450/451 grind. Next, a rev kit for your bike to let it rev a lot more, everybody sells a rev kit, but I have heard that the sparks one is best. You have a pretty decent pipe and I have been told that the stock head pipe flows enough on any built engine, so there is no need for a headpipe change. Gearing, drop down to a 14 tooth, more low end power, little bit less top end. Last, get a sparks step key ignition, only $15, helps low end, and revs even more. With all of the things I have listed, the price should be under $500 if you do the install yourself. If you get theses mods your power output will amaze you, with my mods I kill piped 250RS in the dunes.

Prices- JE piston $130
Cam- $150 With exchange
Rev kit $85- $100
Step Key ignition -$15
14 tooth sprocket-$15

 

You can run premium pump gas with an 11:1 piston, as long as you run a bigger cam. I've been running 11.25:1 comp. with pump prem. for quite a while now with no problems. I add some octane booster to each tank just to be safe. when i put the piston in, i started with a 50/50 blend(race gas,prem. pump gas). Then after a couple of tankfuls, i switched to prem. pump with some octane booster, and i couldn't tell the difference. The plug looked fine and the motor didn't seem too run any hotter. If you want to waste money on race gas, go ahead, but i'm telling you, you don't "have to" use it.

 

tell some facts.....my friend, mx400exkid in chat, and i ride local mx and other flat tracks round here...he has recently had a tc racing cam, rev kit, and springs installed...that along with an fmf pipe and hardened rocker arms for dependability, i have seen him beat 416's, 426's, and even get the hole shot every time on those torquey 440's.....hes installing a piston and getting head work soon....but the point is, he had all that done for around 300 dollars and it flys... i cant wait to see it with apiston and head work......i plan on having the same work as him done pretty soon.....

 

All the work your friend had done had to have costed more than $300. Hardened rocker-arms cost about $200 alone, don't they?

 

Buy a RAPTOR.

 

I didn't see anyone mention a K&N filter, they help alot too, the only drawback is that you have to screw with jetting and that could be a pain.

 

Raptors are junk. thats just my evaluation.

 

I never said anything about buying a Raptor. I wanted to know ways to make my EX faster on the track. I'll keep my 400EX, because it's a HONDA! My mods so far are below.

The local MX track is a 1.1 mile long MX track, with a variety of things on it. From big triples to straightaways to little tabletops. Is there anyone who rides on this type of track that have done any really helpful mods to their 400? I am going to get extended a-arms, new shocks, and then I'll work on the power.

 

How about a 14 tooth sprocket for the front, its cheap and i understand it will give the 400ex a much snappier feel but it will take a little off top end but that shouldn't matter for mx riding. I have a k&n and i have not had to mess with the jetting, my plug looked ok so i left it alone. ANd i dont think it made much difference compared to a foam, just my opinion.