Header or Not?

[WheelieMan4]

What exactly will I get from adding the HMF Header to my slip-on? More power? Noticeable gain?

What do you guys think i should do, because i have a really good deal on one right now...

[prepracing]

I'm pretty sure you can't buy an HMF header pipe separate, you have to buy the whole system. Alot of people run the FMF bowerbomb head pipe with an HMF slipon and get good performance. But if you don't have any motor modifications I would stick with the stock headpipe. A 400ex with no motor mods looses backpressure and some power with an aftermarket header. I have seen 2 identical 400's roll off the showroom, one of my buddies got an HMF slipon and the other one went for the whole system. Both also got K&N filters, both ran 160 mains with no other carb adjustments. The 400 with only the slipon ate the other ones lunch every single time in a straight up drag race, no matter who rode it. Talk about a mad person that spent an extra $200 :mad: and got beat :devil:

[WheelieMan4]

its a used one...thats y i can get it. but what your saying is that they are mainly made for like if u do stuff to the engine(cam, piston, etc)???

[prepracing]

something else I just remembered.....an HMF headpipe will only fit an HMF slip on that it comes with. Because your HMF slipon was made to fit your stock headpipe, its not going to fit an HMF headpipe. May sound dumb, but trust me or call HMF and they will tell you the same.

Originally posted by prepracing
, both ran 160 mains with no other carb adjustments.

were both of these jetted profesionally or did the owners do it themselves? i would say that the ex with the hmf headpipe would need a larger jet due to the fact that a larger headpipe is drawing out more air than the smaller pipe...more air needs more fuel...

there will be noticable gains with a larger headpipe...although the 400ex headpipe was pretty good stock, there are still ways to make it better. i am not sure how the hmf pipe is, it is possible that it may be making more power on the bottom end than on the top, which is where racers want most of their power since they are not running 5th gear, full throttle that much...

that also could be the difference between the 2 ex's

[WheelieMan4]

Originally posted by prepracing
something else I just remembered.....an HMF headpipe will only fit an HMF slip on that it comes with. Because your HMF slipon was made to fit your stock headpipe, its not going to fit an HMF headpipe. May sound dumb, but trust me or call HMF and they will tell you the same.

well that sucks...are u sure?? that would be stupid of them, but i guess i see what your saying...i guess im gunna have to keep the stock header...:ermm:

[blakefoote]

i got the HMF full exhaust for Christmas and it is the bomb....I love that thing...it is prob one of the best upgrades i have done to my bike...

[hondaboy400ex55]

i hear those fmf power bongs are preety good two

[04'400ex'er]

Hopefully this pic can resolve some of these questions. On the left is my HMF silencer from the full system, right is the stock headpipe. Notice after the tig weld how the pipe diameter gets larger. That is the diameter of the HMF header.

[cals400ex]

you can get the header and then send your slip on to HMF and they will remove the piece that your stock header slides into and put a bigger one it to fit their header. i would say it would be worth the gains. you would have their full system with this simple change.