Grinding down head pipe welds...

[motox92]

I was reading that you can grind down some kind of welds inside the headpipe? I'm just wondering where these welds are and whats the point of doing it?

[shawn3389]

its for better air flow...i did mine and i like it

[sprayedgt]

It's the weld slag on the inside of the header where it meets the head. There is really not much of a gain here if there's really any at all. Some factory headers are worse than others, but overall not bad enough to restrict flow. I mean we're only talking about 1/10th of an inch total. IMO not worth the trouble. The factory header is pretty good and plenty big enough if you don't plan on doing any internal engine work. If engine work is planned just go ahead and get a full system. The bottle neck in the stock exhaust is not the header, it's the muffler.

[shawn3389]

mine had alot in it i would say it looked like a 1/8 or more and it must have did something because i had to rejet it after i was done....and its easy to do and worth it too

[dariusld]

Someones elses picture.

[sprayedgt]

I'm sure it helps some. But I wonder how much it really does help. After all the exhaust port on the head is smaller than the header port itself. A rejet is possible because they run very lean from the factory. I had to rejet from a simple UNI filter. Popped like crazy on decel. It wouldn't hurt to do it. It was an option for me but I opted for the whole system. It wouldn't hurt to pull it off and take a look anyway. If it's bad grind it.

[rideracelivemx7]

personally i didnt notice much of a difference at all, i dont htink it was worth my time, i broke alot of bits on the dremel too lol the nearest hardware store didnt have any suitable carbide bits

[motox92]

Alright, I got my 450r carb on the way..along with the sparks timing key and sprockets...hopefully I will see some kinds of gain

[MAKO19]

I just did mine and I believe it helped, especially with a slip-on pipe. My welds were nasty especially on the left side (way uneven).

Even though the port may be smaller the weld will create added turbulence within the header which is not good. Once the valve opens the exhaust gas tries to smooth out leaving the port but is immediately interrupted by these welds and becomes turbulent again. Smoothing out this area will smooth out the flow making it more laminar and this decreases the pressure drop through the pipe. In other words, it will take less energy to get the exhaust through the pipe and the thus the engine is working easier. I also believe that since we are dealing with small engines (approx. 35-40 HP) that they respond well to these smaller scale modifications than larger engines would.

Scientifically speaking it make sense but I would like to see the results on a dyno just to see what it actually does. It won't hurt to try though since this mod is free and only requires time and labor. Good luck and have fun!

[brian76708]

Originally posted by MAKO19
It won't hurt to try though since this mod is free and only requires time and labor. Good luck and have fun!

exactly the only thing you have to loose from doing it is some time and maybe a few bits. i did it to mine but my quad is not back together yet and ive done motor work so there will be no way for me telling if it worked hhaa.

I did it. Could I feel a difference? Not a bit but I didnt expect too, its like free HP when you think about it so why not. Mine was not bad at all to begin with, it was almost as if somone already did it. It seems they made the 400ex parts better on the older ones.

[honda400ex2003]

i did mine just because. It helps with the vibration in the pipe too. The turbulence it makes made mine sound very funny when revving up at about 4500 rpms. It sounded like a whining for only a second and then would quit. It got irritating so at least if anything it helped with that. i have head work done and the 416 all at the same time so it was hard to tell what made the most it all works together great though. Steve

[hornetgod13]

Originally posted by dariusld
Someones elses picture.

Mine. Nice to see it helped. :macho

[crxjarred]

do u have to repalce the crush gaskets if u do this ?

[shawn3389]

i did but mine needed news one before i did it

[sprayedgt]

Anytime you take the header off you should replace the gasket. They say you can reuse them but I'm not a fan of reusing gaskets. Especially crush seals. Once they're crushed they're done.