I got into the garage this morning with a plan to make a new exhaust for the KLX. KTM muffler and Muzzy header, both dirt cheep Ebay scores.
Not gonna happen, it would take too many bends and pipe diameter changes to make it all work. Way too much work....

I still think the Q4 I have now is too loud, but I guess I just have to try to make sore "quiet tip" for it.

Anyhow, I then decided to try how the Muzzy header would work with the Q4 muffler. And they were actually pretty easy to fit together.

With everything else staying the same, I was curious to see what difference the bigger header would make. It makes a big difference.
I'm ready to admit the low-end is little softer than with stock header but at the top the difference is really big.
With my current gearing and the TM36 carb, on 6th gear with stock header the bike pretty much topped out at 8500RPM, it would accelerate very slowly from there on.
With the bigger header it pulled straight up to 10000RPM.

Only a dyno test would show more details about how the torque curve changes but just a top-speed test shows very strong gains at the top.

--
Mikko

The

 

I saw gains everywhere with the bigger FMF header, but was quickly told that I was wrong.
It could not be.

Maybe I was right after all.

Ride it some more. A week after I did it, i was noticing not only more power, but more torque, in all different situations.

 

You are both so wrong.

Smaller diameter header = Moar Powha. I installed a header from a 49 cc moped on my KLX and can now do 9th gear power wheelies.

 

Yup = I stuff old socks in my muffler.. it runs better! Need that Back pressure man.. quieter too

 

It should also help to block off half the snorkel into the airbox...

 

And whatever you do, don't remove the backfire screen. Not only does it make your bike slower it will, in all likelihood, explode like a 72 Pinto rear ended at a stop light.

 

I posted it before but I was amazed at the changes brought on by the powerbomb I put on. It was larger diameter than the stock piece so I was sure it would affect the top end and if anything hurt the lower end where I ride off road. I was wrong it gave a nice boost down low and sure didn't take anything off the top. Something I will add as I've jetted for my pipe and am still a little rich I pulled the airbox lid, I've ran it without a snorkle since the jets. I found a good increase on top but at the expense of some low end so I put the lid back on, still less the snorkle.