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O200 Performance Exhaust

A properly built(tuned) 4-1 exhaust should net 8-10 hp on 0-200.I have built a prototype but won't have any data for a a while.I have had it on the airplane but as with anything the first is a starting point.There is more to it than meets the eye if you really want it to work.I will say that the stock 0-200 exhaust is really bad even for an old farm tractor.
I expect by the time I am done I will have a lot of scrap tubing but I will know what works.
Just think about this--The mathematical ideal individual pipe length for that engine and rpm is about 80 inchs:roll:

Karen
 
willyb said:
….Just think about this--The mathematical ideal individual pipe length for that engine and rpm is about 80 inchs:roll: Karen
Click to expand...

This made me think about motorcycle exhaust pipes back in the day.
I remember early 2 stroke dirt bikes (like the Greeves) having just short straight pipes,
but then the "expansion chamber" exhaust systems caught on.
You could buy them ready-made, but at some point DIY expansion chamber kits were marketed,
with an assortment of differently configured cones and different size / length pipes.
I assume that the "mathematical ideal" pipe length has to do with the ideal amount of back pressure...
is it possible to use shorter smaller exhaust pipes to achieve that goal?
 
Pipe length is based on the physics of reflected waves.
When the exh valve opens a pressure wave is sent down the pipe causing a void behind it.This will actually put a vacuum in the cylinder.If the vacuum is present when the intake starts to open on the overlap(both valves open) it can aid in cylinder filling.Now the big issue here is that gas flow pulses in the pipe because and open ended pipe will send a negative pulse back toward the engine.So gas flow pressure waves act like a slinky in the pipe.The trick is to time the pulses to be in harmony with the rpm where you want the power.Lots of factors involved more than just pipe length which you could look at as time.Long pipes for low rpm and shorter for higher rpm.

The expanding cone of a two stroke pipe creates a larger void behind it thus creating a negative at the exhaust port.The convergent or opposing cone turns the pressure wave around and sends it back towards the exhaust port.That pulse is timed to get there just before the exhaust port closes.Sometimes a 1/4 difference in pipes can be felt in the power curve on a motocross bike.

Karen
 
All kinds of interesting devices.Variable intake runner size,resonance chambers on intake and exhausts,variable valve timing.It goes on and on.Most has been tried just whether it is practical on a particular application.Fun to play with all of it.
 
willyb said:
Pipe length is based on the physics of reflected waves. When the exh valve opens a pressure wave is sent down the pipe causing a void behind it.This will actually put a vacuum in the cylinder.If the vacuum is present when the intake starts to open on the overlap(both valves open) it can aid in cylinder filling.Now the big issue here is that gas flow pulses in the pipe because and open ended pipe will send a negative pulse back toward the engine.So gas flow pressure waves act like a slinky in the pipe.The trick is to time the pulses to be in harmony with the rpm where you want the power.Lots of factors involved more than just pipe length which you could look at as time.Long pipes for low rpm and shorter for higher rpm. The expanding cone of a two stroke pipe creates a larger void behind it thus creating a negative at the exhaust port.The convergent or opposing cone turns the pressure wave around and sends it back towards the exhaust port.That pulse is timed to get there just before the exhaust port closes.Sometimes a 1/4 difference in pipes can be felt in the power curve on a motocross bike. Karen
Click to expand...

Sounds like black magic to me!
I can see how people can design this stuff nowadays with computer modelling,
but back in the day when slide-rules were the norm I think it was actually more a black art than science.
 
hotrod180 said:
Sounds like black magic to me!
I can see how people can design this stuff nowadays with computer modelling,
but back in the day when slide-rules were the norm I think it was actually more a black art than science.
Click to expand...

Drag racers drew a crayon line longwise on the outside of the pipe aft of the header collector. Where the color changed they cut it off to tune it

Glenn
 
Last edited:
There are a number of calculators on line to calculate the proper header tube size and exhaust length based on what RPM you want the peak power. Google "calculating tuned exhaust length" should do it. I used them to calculate the header size and length when I built the exhaust for my other plane that uses an O-200 about 10 years ago. I don't have the skills or equipment to build a full 4-1 header system, so fabricated a system with four separate exhaust stacks. The calculations I came up with were for 1-3/8 ID pipe size, and a 74" header length for the low rpms of an aircraft engine. Since I don't have the room for that long of header pipes, I used 1/2 wave length and built them to as close as I could come to 37" header length. That showed a significant improvement in performance from the old 2-1 exhaust logs I had mounted to either side of the engine before.

-Cub Builder
 
cubdriver2 said:
Drag racers drew a crayon line longwise on the outside of the pipe aft of the header collector. Where the color changed they cut it off to tune it

Glenn
Click to expand...
Yup that is the way we started to determine collector length.Just a starting point but it does work.
 
Cub Builder said:
There are a number of calculators on line to calculate the proper header tube size and exhaust length based on what RPM you want the peak power. Google "calculating tuned exhaust length" should do it. I used them to calculate the header size and length when I built the exhaust for my other plane that uses an O-200 about 10 years ago. I don't have the skills or equipment to build a full 4-1 header system, so fabricated a system with four separate exhaust stacks. The calculations I came up with were for 1-3/8 ID pipe size, and a 74" header length for the low rpms of an aircraft engine. Since I don't have the room for that long of header pipes, I used 1/2 wave length and built them to as close as I could come to 37" header length. That showed a significant improvement in performance from the old 2-1 exhaust logs I had mounted to either side of the engine before.

-Cub Builder
Click to expand...
Your numbers are correct according to the established formulas and a good place to start.No doubt it is way better than the stock exhaust by far.It will try your patience attempting to maintain equal length pipes and route them around everything to get them to a common collector.Many of the turns cannot be done on a mandrel bender as they are compounds so tube sections must be hand cut and welded.Lots of fun.
 
WillyB/Karen, thanks for a really interesting discussion. You mentioned the search for the optimum pipe length; there must be an optimum pipe diameter, too, in order to create the desired vacuum. Can tell us more about that?

This discussion makes me wonder if there’s a program that models exhaust gas behavior. Probably so, but no doubt it’s proprietary.

Very interesting stuff. Thanks for sharing your insights.
 
Speedo said:
WillyB/Karen, thanks for a really interesting discussion. You mentioned the search for the optimum pipe length; there must be an optimum pipe diameter, too, in order to create the desired vacuum. Can tell us more about that?

This discussion makes me wonder if there’s a program that models exhaust gas behavior. Probably so, but no doubt it’s proprietary.

Very interesting stuff. Thanks for sharing your insights.
Click to expand...
You are correct.Pipe diameter is a major factor.A good starting point is the size of the exhaust valve.Velocity is absolutely related to pipe diameter.The bigger is better way of thinking can really hurt you.Gas speed also varies with the temp of the gas.There are some applications where stepping the size(usually down) at some point along the length is beneficial.
An aircraft engine is so limited by low rpm that you want all the torque you can get and flow velocity is critical to making that happen.
 
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