How about someone educating me on this one :biggrin:
In theory, a longer pipe would be used for lower rpm power and shorter for high rpm.
http://www.engr.colostate.edu/~allan/fluids/page7/page7.html
http://www.engr.colostate.edu/~allan/fluids/page7/page7.html
4 Cycle Karting Forums - Exhaust Pipes
Mainly the science behind loop pipes, but may help with others
Mainly the science behind loop pipes, but may help with others
We have made hundreds of dyno pulls testing dozens of various headers over that last 10 years. We have backed that up with track testing on both short (hi torque) and big (high RPM) tracks. End result is Hondas like long pipes. 42" seems to be optimum length. These motors show improvement in both low and high rpm as the length is increased, although it tends to be more noticable at the higher rpms. To optimize, pipe diameter needs to be matched to the motor (and rpm range). Stock (with gov removed and correct jetting) like a 1" OD pipe, going up to 1 1/2" for 20hp 8000 rpm Hondas. 1 1/8 to 1 1/4" seems to work best on the majority of the motors.
Of course the reality is you must use what fits the chassis (and rules if racing).
NR-Racing.com
ex
i dont know if this would help someone or not on a 3 cyl 2 stroke saab that
was set up for racing,the ex pipe went frome 1 1/2 " to 2 1/2" with of corse
a tuned muffler,to get the max h/p, we would shove a broom stick in to
the pipe,,when the ex got the loudest we would mark the stick,pull it out
if the mark was 9 " or what we would cut the pipe,,maby that was a bunch
of crap,but that is how we did it earley 60 s, of corse a lot of other things
were done to get a 3cyl up to 85-100 mph on ice,,man i wish i could go
back to the day.:thumbsup::thumbsup:
i dont know if this would help someone or not on a 3 cyl 2 stroke saab that
was set up for racing,the ex pipe went frome 1 1/2 " to 2 1/2" with of corse
a tuned muffler,to get the max h/p, we would shove a broom stick in to
the pipe,,when the ex got the loudest we would mark the stick,pull it out
if the mark was 9 " or what we would cut the pipe,,maby that was a bunch
of crap,but that is how we did it earley 60 s, of corse a lot of other things
were done to get a 3cyl up to 85-100 mph on ice,,man i wish i could go
back to the day.:thumbsup::thumbsup:
We never run a 42" long pipe on mansville.
But we do like long pipes. The size of it is determined by the exhaust port. The exhaust port is determined by the exhaust seat I.D. So if you have a 27mm exhaust valve, you usually have a 1" I.D. exhaust seat. So you port match the exhaust port to 1" all the way through. Then have a header first stage of 1" I.D., which means the O.D. may be about 1.125". That's just the first stage, and the length of it depends on how much torque curve your trying to use. longer more torque, shorter more horsepower.
The second and third stage are always bigger, and must be slightly shorter then the stage before it. For an example. If the first stage 8" long the second is usually 6" and third is 5". So you end up with a 19" header. The first stage needs to be at least 2" longer than the second stage. Because when you measure inside of the pipe it's shorter because of the first bend from the flange.
The stages get shorter because the exhaust fumes want to escape more and more as they reach the end, and usually makes for a much louder sound when it finally escapes.
Having the pipe going straight back is just the shortest way for it to escape. Mainly because we are drag racing, and we do like to have are motor turn high RPM's.
But we do like long pipes. The size of it is determined by the exhaust port. The exhaust port is determined by the exhaust seat I.D. So if you have a 27mm exhaust valve, you usually have a 1" I.D. exhaust seat. So you port match the exhaust port to 1" all the way through. Then have a header first stage of 1" I.D., which means the O.D. may be about 1.125". That's just the first stage, and the length of it depends on how much torque curve your trying to use. longer more torque, shorter more horsepower.
The second and third stage are always bigger, and must be slightly shorter then the stage before it. For an example. If the first stage 8" long the second is usually 6" and third is 5". So you end up with a 19" header. The first stage needs to be at least 2" longer than the second stage. Because when you measure inside of the pipe it's shorter because of the first bend from the flange.
The stages get shorter because the exhaust fumes want to escape more and more as they reach the end, and usually makes for a much louder sound when it finally escapes.
Having the pipe going straight back is just the shortest way for it to escape. Mainly because we are drag racing, and we do like to have are motor turn high RPM's.