Exhaust Open exhaust

[Mountainman]

science ????

If you want the look of straight pipe, but still want to have backpressure, take a washer, and grind down the OD to fit inside the pipe. Then just weld it in

well I think that most will tell us

there is way more science to it than that

although up top the mountain -- been known to do things such as this

ride the motor bike thing

 

[jlebh1]

what about the exaust that barry makes im pretty sure it has no baffle I might ask him...

 

[Gungatim]

I'm no expert by any means, and I am sure your are correct that there is a science to it, but I have run several 2cycle motors with no exhaust at all with no ill affects. I had solex moped that the exhaust got torn off after it was stolen and recoverd, I rode it for 2 years that way and it never had a problem, also, my scooter project (2 cycle tecumseh) ran with just a 6" piece of straight pipe with no backpressure just fine all summer. Granted, these are not the HT motors, but if you look at the stock exhaust, it wouldn't be too hard to get an equivalent in/out air flow ration with a piece of pipe and washer.

Any exhaust experts out there care to comment on how to calculate backpressure? I know there's alot of info on calculating tuned expansion chambers, but all I can find (from the 2 stroke tuners handbook) says"outlet pipes should have a diameter .58-.62 times that of the lead in pipe, and the length 12 times the diameter"...if you go too far in restricting the flow, there will be a slight decrease in power and the engine will run hotter.

I say play around with a few designs and let us know what you find.

 

[biken stins]

There was a baffle you could put in pipe and adjust it. Basic washer with a stud mounted. Stud went through a hole drilled in bottom of pipe. Adjustment was just turn a nut then locking it with another. Better acceleration-lower top end when open and opposite when closed. seems like with a control to work it with out stoping might be a way to go. a choke wire control to baffle ?. Anyone try a flame thrower on them yet ?
Plug in exhaust, wired to switch,wired to white wire ?

 

[jlebh1]

is this on barrys chopper exhaust?

 

[Gungatim]

That is an interesting concept for an adjustable opening to vary the backpressure. If I get some spare time, I may play around with an exhaust made from pipe, with a T-fitting that I can put a pressure guage on, and a ball valve at the end. Then I could adjust the flow and measure the pressure in the pipe. Be nice to know exactly what amount of backpressure is healthy. Of course, a tuned expansion chamber is best for performance, but not so easy to build.

 

[jlebh1]

does anyone know if the pipe that barry sells on ebay has a baffle? because if not I can make something very similar at work

 

[Irish John]

I've run my Honda with just the long pipe of the poo poo exhaust and the silencer disconnected. It sounds like a racing bike and it really is a great sound. Very quick throttle response as well. I'd love to ride it occasionally like this but would the lack of back pressure stuff the engine and, if so, how would it cause damage?
My neighbour thought it was a racing car when he heard the motor.
Is it the valves that need the backpressure?

 

[jlebh1]

with a 4 stroke it doesnt matter just look at all the choppers and harleys that just run pipe without a baffle we are talking about 2 stroke engines here

 

[fetor56]

4-strokes ONLY.

I've run my Honda with just the long pipe of the poo poo exhaust and the silencer disconnected. It sounds like a racing bike and it really is a great sound. Very quick throttle response as well. I'd love to ride it occasionally like this but would the lack of back pressure stuff the engine and, if so, how would it cause damage?
My neighbour thought it was a racing car when he heard the motor.
Is it the valves that need the backpressure?

I doubt if it would stuff the engine.What it would do is cause the gasses to escape quicker...the engine would run leaner & hence hotter.If u want to rejet the carby that problem would be solved.