Expansion chamber

Then you don't need an expansion pipe, you need a smaller rear sprocket. Go for a 36t.

Depends on if you want acceleration to go with that speed... I'm going 43mph with the 44 tooth sprocket that came in the kit, but it takes more than just a good expansion chamber to do that...

For the good expansion chambers, there's only 2 of them you can buy for these that I'd recommend, and I'd still recommend modifying a dirtbike pipe over buying a modified pocketbike pipe, but the SBP pipe performs and so does the Snake pipe sold by Arrow Racing. They're both modded pocketbike pipes, but they do work well.

A cheap eBay Dirtbike pipe for a bike in the 65-90cc range.

Look around you can probably find one for around $40-$50.

Then use this to mount it to the engine:

http://shop.crmachine.com/product.sc?productId=105&categoryId=21

-One of the "Fire Breather Header Kits"


Cut-cut-weld-weld.

If you don't weld, take it to a muffler shop with the exhaust, the manifold parts, and your bike. Probably end up spending another $40-$50 to have it cut and welded to fit the bike.


$80 - $160 depending on your fabrication proficiency and eBay skills, and hands down the best exhaust setup you can run on these engines.