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Old 05-03-2014, 02:15 AM
Techbiker Techbiker is offline
Motorized Bicycle Elite Member
Join Date: Oct 2009
Location: DFW, Texas
Posts: 165
Default Re: Standard Horepower?

Expansion chambers help a ton too! I threw a billet intake and SBP expansion chamber exhaust on my 69cc thatsdax HT and it really opened up top-end power. It wasn't really scientific but I rode up a steep, long hill in the countryside a few times with the expansion chamber and with the stock exhaust at full throttle. Both times I approached the hill at 26 mph.

With stock exhaust, my speed dropped to 15mph half way up the hill. I had to pedal assist to make it to the top quickly.

After installing the expansion pipe, my speed dropped to 22mph half way up.

I gain of 7mph under heavy load was very significant! I was limited to around 26 mph due to engine vibration anyway. The only issue with the SBP expansion chamber was the noise.

If your expansion chamber is non-adjustable, you may consider lengthening or shortening it to maximize the performance gains where you want them.
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