Those are some great ideas. With stock exhaust, I'm wondering just how much you can open the airbox and do any good, seeing as how it's so restricted at the tail end. Would like to get a better exhaust, but those things are darned expensive!

 

Ebay, mate...Look for a KLX 300 full exhaust (header and can) or a KLX 250D exhuast system. Both will open up nicely.

One thing you can do is take the head pipe and get a dremel tool or a die grinder and grind down the weld inside. That helped me a bit. And if you dont care about your stock can you can get a ...what is it it...1/2" bit and drill straight back through the spark arrester. Or get a hole saw and cut out the end...and or torch/plasma cutter.

That'll open ya up a bit.