modifying stock 400ex pipe for better flow

[slamdak8782]

Im in the process of changing 400 to 440 11-1 hotcam iwas wondering if anyone ever modded their stock pipe for a better gain and also if their is a substitute for exhaust packing On the pipe issue from looking at it. i think i would be good for flow to grind the excess weld from the inside were it meets the head

[darkstar]

Doing all that work to make a stock pipe better is a waste of time you can go and buy an hmf slip on for like 200 something and they are great.You should also re-jet your carb and you well be as good as new.

[darkstar]

And if you are putting money into the engine you really do not want the stock pipe on.

[400exrider707]

Originally posted by darkstar
And if you are putting money into the engine you really do not want the stock pipe on.

Enuff said. I bought my FMF Ti-4 brand new for about $200 including the mid-pipe.

[khen]

If you have a angle grinder with a cutoff wheel and a welder you can convert the stock exhaust to a straight through shorty pretty easily. I did mine in less than 1 hour and about $7 worth of parts/supplies. It's suprisingly light and much more durable than the POS aftermarket I had before it. It also sounds and performs great and I can wheelie without concern of it hitting the ground.

[slamdak8782]

im starting to agree with those that said get a new pipe but one thing i was wondering if there is a header pipe that is made aftermarket that is even with the head as far as the diameter of the pipe i took mine off today and there is a pipe slid in and then another underneath it stepping it down two sizes what im looking for is a pipe with large enough diameter to match the head where it connects to the head. The stock pipe is obviously not port matched to the head. I am looking for larger diameter pipe that is like a large tube header. ive already ported the exhaust ports out to copper gasket which will improve flow immensely. Also im getting pissed about after market companies only doing enough to improve things marginally with their parts. Like the wiseco 11-1 i got. its lighter but not built to the quality that ive seen in the trx450r piston. If they would build the parts better my 400ex would dominate 450s:blah:

[darkstar]

ok, just go with an HMF full system with your modded exhaust ports this well work really good and you well need to jet your carb.

[slamdak8782]

anbody else have something? what did the one guy mean about a shorty header? Anybody ever dremel the welds at the header for increased flow

[walt miller]

with a 440 i would buy a full pipe. i have a 416 that i drilled a bunch of 9/16 holes in the baffle of the stocker and put an HRC end cap on it and it runs good