I am looking at buying a 400EX. Actually 2 of them but thats besides the point. If I were to buy it with a DMC exhaust... say that gives an average of 5to6 hp automatically w/ a K&N filter and jets. Say that puts me at about 30to31 hp. Thats pretty good but i still won't out run other bikes by much. what if i were to put a 10.5:1 compression Wiseco piston in it? How much more power will I gain? I still want reliability and want to be able to run about 90 octane gas. So a radical engine bore is out of the question unless you can prove that i won't have to have it serviced any more often than a stock engine.

 

Red,,

Since you already will have the DMC exhaust and K&N air filter, all you need to add are following items...
450/451 grind cam from WebCam
11:1 coated piston from LRD Performance
CDI Module from CT Racing
And if you can afford it, add the 39mm FCR carb from LRD Performance.

If you dont want to go to a big bore I would suggest that you at least go to first oversize and install the noted piston. That way you will have a fresh bore and reliability.. I would also suggest that you do a mild sport port or at least match port the exhaust and intake. You would be surprised as to how mismatched they are from the factory...
You will end up, with the carb, around the 36 or so HP..... Great off the line and a study hard pull throughout the gears...

Any questions about any of the parts or porting email me. I have all this and more and it is very reliable and fun to ride.. and yes, it all runs on 91 or 92 octane fuel

 

Thanks! that helped a lot. Hopefully I'll be able to find a 400ex soon!

 

Do you all realize how a powercurve works and how gains work? Because you get a 6hp gain from a pipe, it is usually only for a short duration in midrange power, not at top end. It is all advertising ploy. To get to 35hp you need at least a 416 kit, different cam (to move the powerband up)higher comp piston, porting and polishing, etc...

 

a new pipe and jetting and a filter will not drastically change your top end hp, i have a Stroker SX-1 muffler, K&N Airfilter and jet kit, i didnt notice maybe more then 4 mph gain on the top end but i have great low and mid range power that can pull harder and faster, you could keep your stock exhaust and just get a 415, or 416 piston, new cam, and a port job done and that would give you a better top end i believe but i am not positively sure all about that

 

From what i have heard and seen porting doesn't help a lot. All you need is port matching or play porting. Full blown porting is more money and for what, it averages about nothing. hakmazter is right 416 is the way to go. and buy an xr cam instead of a web, cheaper and no new valve spring. You might want to go 3 angle valve job to make the head flow stronger.