Exhaust Header Tips
When configuring your minibike exhaust there are a couple thing that you'll have to make a decision on. Of course the first thing would be the sound level. Loud or quiet. There are a variety of stock type mufflers available to fit most small engines. If you want quiet, best bet is to stick with the original. Tecumseh and Briggs spends tons of money on research and development and have designed their stock mufflers to to run as quiet as possible without sacrificing engine performance. If quiet just isn't your thing, heres a quick guide to help with your custom header.
All engines need back pressure in order to build torque throughout the RPM range. Not enough back pressure and your bike will roll off the line like a slug unless your drag racing with a high RPM engagement clutch. Too much back pressure and your engine will choke. You have to experiment with the length and diameter of your header to get just the right combination for your style of riding. What ever your decision, you will need to re-tune your carburetor to compensate.
When selecting a header length use this formula:
Longer length = More bottom end / Larger diameter = More top end. Example: A long pipe will provide lots of bottom end. However, If you keep the length the same but increase the diameter your power range will move toward the top end.
Shorter Length = More top end / Smaller diameter = More bottom end. Example in contrast: A short pipe will provide lot's of top end. However, If you keep the same length but decrease the diameter your power range will move toward the bottom end.
In general. Bottom to mid range headers are best for all around use and provide good engine performance. Top end headers are not recommended unless you plan on running wide open full time. Either way...It will be loud!
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Happy Trails, Chuck at Valley Farms.