exhaust pipe diameter

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Frogster

New Member
Jan 18, 2013
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Mississauga Ontario Canada
Hi there everyone. I have an SPB expansion chamber, and I would like to weld out my own pipe for it using larger diameter pipe then the piping provided in the kit. The kit uses 7/8ths (0.875") inner diameter piping to lead the exhaust gases to the expansion chamber. The piping and prebent elbows I want to redo it with are 1.000"-1.100" inner diameter. Will the large diameter plumbing leading up to the expansion chamber help with performance? The only thing thats holding me back is that ive heard these piston ported 2 strokes like having some back pressure.

Can anybody give me a physics lesson?
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
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memphis Tn
Without a fully ported cylinder, I doubt you will notice much increase in power if any.
That being said, build it your way just for the satisfaction of having a custom pipe.
 
Desert Rat

Desert Rat

New Member
Jul 30, 2012
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Apache Junctoin Az
Frogster said:
Hi there everyone. I have an SPB expansion chamber, and I would like to weld out my own pipe for it using larger diameter pipe then the piping provided in the kit. The kit uses 7/8ths (0.875") inner diameter piping to lead the exhaust gases to the expansion chamber. The piping and prebent elbows I want to redo it with are 1.000"-1.100" inner diameter. Will the large diameter plumbing leading up to the expansion chamber help with performance? The only thing thats holding me back is that ive heard these piston ported 2 strokes like having some back pressure.

Can anybody give me a physics lesson?
Click to expand...
This might help you
www.Filecrop.com
type in "two stroke" you will find all sorts of 2 stroke manuals all free
hope it helps
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
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memphis Tn
Go for it! I doubt you will notice much power increase but you WILL have a cool custom built pipe!
 
S

Scootmeister

Member
Mar 15, 2011
243
5
16
North Carolina
Hi Frogster, keep in mind that everthing about Chinese kits is based on price point. Kit pipes are designed to be cheap and quiet, which means restrictive. As you have noticed, most are 3/4" or 7/8". Many stock 50 cc motorcycles and mopeds with 2 strokers, on the other hand, are deigned for performance and come stock with 26mm header pipes, a tad over 1". A 1" header will give you plenty of back pressure and allow your engine to breathe with the help of an upgraded carb and expansion chamber.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
22
0
memphis Tn
If you have a fully ported cylinder, upgrading pipe size should help top end power quite a bit. You can adjust backpressure with a muffler at the end.
 
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