Straight Pipe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
235
63
up north now
I live in an "urbanized township". There are five bars on the cross road 500' from my house, and a park on the side of my house.

You can only imagine what I hear all day and all night. Plus the heroin dealer two doors down from me.....
 

Tony01

Well-Known Member
Nov 28, 2012
1,386
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sf bay area
Run the dam thing with a Straight Pipe. BIG difference....YW
Why are you pushing this viewpoint? It makes your engine much louder and probably run worse. Don’t start multiple threads to give bad advice-

 

mapbike

Active Member
Mar 14, 2010
5,398
11
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Central Texas
It's no louder then a lawn mower. You should hear what passes this house.
I'm Tame ~

Not that it matters, but my all time fastest china girl bike did 52 mph with a straight pipe exhaust and I built others that would cruise at 40-45 mph with straight pipe, they pulled moderate hills good even with 34T & 36T sprockets, so if the noise isn't to much for someone personally and/or the area they ride, its the best bang for the buck to add extra speed and power if the engine/carb. is tuned right and all else is setup right.

Not everyone can afford a custom expansion chamber pipe or they don't have the tools needed to build their own.

This was my experience anyway and that all I have to go with.
 
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bobo60

New Member
Nov 23, 2019
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I built this Zeda PK100 on a Diamondback Outlook and it was okay with stock muffler, but I took a handle from a fetrilzer lawn spreader and cut it, took a old stock muffler and cut off the muffler itself and welded the tube to the pipe, and at the end put a plain 6" tubular lawnmower muffler on it. It's a little louder, but this baby went from 37mph to 51 mph with a little adjusting richer of the needle clip due to backpressure change. Well worth the time and if you don't weld, just drill through both pipes and run a bolt through there and that'll work also. Much improved everything power wise and I go by so fast the neighbors think I'm a jet...
 

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mapbike

Active Member
Mar 14, 2010
5,398
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Central Texas
I built this Zeda PK100 on a Diamondback Outlook and it was okay with stock muffler, but I took a handle from a fetrilzer lawn spreader and cut it, took a old stock muffler and cut off the muffler itself and welded the tube to the pipe, and at the end put a plain 6" tubular lawnmower muffler on it. It's a little louder, but this baby went from 37mph to 51 mph with a little adjusting richer of the needle clip due to backpressure change. Well worth the time and if you don't weld, just drill through both pipes and run a bolt through there and that'll work also. Much improved everything power wise and I go by so fast the neighbors think I'm a jet...

I have been out of this game for the last few years, so even though Ive heard about and seen these PK100 / YD100 engines online, I have zero experience with them.

seem interesting though for sure.

Im curious about how well balanced these engines are compared to the typical PK80 or GT5 type engines.
 

bobo60

New Member
Nov 23, 2019
11
7
3
60
it has a lot of bucking and lurching at low rpm, kida like a hotrod with a real radical cam in it, but once you give it just a little gas it smooth right out and is almost like a 4 stroke until you hit the powerband. Mine seems to get a second wind from 7/8 throttle to WOT, and seems like the rpms almost double at the end. The difference in low end torque, mid range acceleration and WOT top end belies the fact it is only increased 13cc, and is almost double the performance improvement from a 49cc(really a 37cc) to a 80cc(really a 66cc) as this ones total displacement measured in US standards is 79.54cc. The compression is up as if your not going about 10mph or faster even with new tires it just skids the rear wheel. I live by a steep decline so I usually just get going about 12and then it breaks compression enough to turn over and usually 1-3 revolutions and its running.
 
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mapbike

Active Member
Mar 14, 2010
5,398
11
38
Central Texas
it has a lot of bucking and lurching at low rpm, kida like a hotrod with a real radical cam in it, but once you give it just a little gas it smooth right out and is almost like a 4 stroke until you hit the powerband. Mine seems to get a second wind from 7/8 throttle to WOT, and seems like the rpms almost double at the end. The difference in low end torque, mid range acceleration and WOT top end belies the fact it is only increased 13cc, and is almost double the performance improvement from a 49cc(really a 37cc) to a 80cc(really a 66cc) as this ones total displacement measured in US standards is 79.54cc. The compression is up as if your not going about 10mph or faster even with new tires it just skids the rear wheel. I live by a steep decline so I usually just get going about 12and then it breaks compression enough to turn over and usually 1-3 revolutions and its running.

Thats all good to know, at some point Imay give one of those engines a try and see for myself what they're all about.

Do you recommend a particular place to get them at?
 

mapbike

Active Member
Mar 14, 2010
5,398
11
38
Central Texas
kool, I'll have to check his thread/info out

I have ran straight pipes on several engines and found the performance to be what I wanted, so I kinda stuck with them except for the SBP exansion pipe on one engine that has worked fairly good.