Factory header mods: the skinny.

[tomacGTi]

For those of us that still have the factory head pipes and don't have the coin for aftermarket, this should get you about 80% there. This will not give you the ability to look and R6 in the eye on a straightway but will give you more rev up top and better throttle response. Be advised though that these mods are non-reversible and you could inevitably screw the pooch if you mess up. First:

http://forums.banditalley.net/index.php?topic=11870.0

Is a great description of how to grind down the header flange welds as well as removing the collector restrictor. This is what I've found:

There is no sense in doing extensive airbox mods aside from removing the snorkel if you run the stock headers/slip on. The restriction is great enough that you will find the bike running out of oomph at higher revs in 4-5-6 gear. You cannot jet around this either and more holes will not help matters any, all you'll do is just burn more gas and make more noise.

After I modified the header flange (already had the collector gutted) the bike leaned up. My bike was already jetted for a snorkel-less airbox (42mm dia), slip on, freer flowing airfilter and everything became lean. Since it was flowing more out, I decided to try an airbox lid that I had previously modded with a 50mm diameter opening/snout. Jetting is now:

-3.5 turns out
-3.5 clip DJ needles
-14.5 float height
-117.5 main, stock pilot jet
-50mm snorkel with UNI green foam filter
-fully modified header/slip on

I previously ran a 107.5 main with the only difference being airbox lid and the OEM header flange. For reference sake, a stock snorkel interior is about 35mm in diameter, my new snorkel is 70% larger at 50mm. What will all of this messing about do?

Good:

-Throttle response becomes snappier
-Full throttle in higher revs at higher gears will yeild more power to redline
-Low end is more responsive
-Pipe actually seemed to quiet down a bit (I wear earplugs anyway but it is noticable)

Bad:

-Midrange is a little flatter versus my previous setup but the response and speed the revs pick up make it unnoticable

-Mileage revving the snot out of the bike will bring you into the low 30's, which you will inevitably do.

-Jury is out on durability of grinding the header welds. They should thoeretically be strong but if you go too far, you can take away enough material that the flange may separate. If you are judicious and do not go hog wild it should not be a problem.

I don't have any pics of my header but the images from the Katana page are similar, eerily so. I did mine before referencing the page and I ported mine to match the transition of the pipe and smoothed edge coming out of the motor.

Apparantly this is a widespread mod for dual-sport guys and they've shown some durability, but still, caveat emptor.

Good luck!

-Randy