Exhaust theory, maybe somebody has tried it?
08-23-12, 12:24 PM
#1
Environmentally-Hostile
Thread Starter
Exhaust theory, maybe somebody has tried it?
We all know that the high energy exhaust pulses from a rotary engine tend to have a negative effect on the exhaust sound. Without a turbo, they tend to get very pingy and metalic sounding, especially with a long tube style header.
This is the sound I'm talking about:
(if somebody owns this car on the forum, no offence intended)
The sound is most apparent at 1:25.
My own car makes the same sound, albeit less of it because I carefully selected and located the mufflers:
If you took a 12" section of standard exhaust tubing, and struck it with a fork or something, it would resonate at it's natural frequency. It would make probably much the same noise as the above video. Now if you held that pipe, you would dampen that noise and it wouldn't resonate (ring, make noise, etc) at all. Obviously you cannot hold the exhaust while you are driving (for a variety of health and safety reasons) but it is possible to wrap the entire exhaust in heat wrap.
My theory is that this heat wrap will dampen the natural harmonics of the exhaust tubing and allow the exhaust to sound much smoother without the harsh metallic-pipe-being-drummed-on kind of sound. Basically, I'm looking for the *sound* of a short-pipe 13b, like this:
Only far quieter by way of several mufflers, and without the rasp associated with a long exhaust system.
Of course this is just a theory that would have to be tested, so I'm just curious as to whether or not anybody ever has tried this? Mostly so I don't waste my time, energy, and money on something that is invalid.
edit: Also, hot exhaust has more energy than cold exhaust. The heat wrap might have a slight performance benefit if it can keep more energy in the pipe (more energy, more velocity?) instead of disippating it. Probably result in more flames too.
This is the sound I'm talking about:
(if somebody owns this car on the forum, no offence intended)
The sound is most apparent at 1:25.
My own car makes the same sound, albeit less of it because I carefully selected and located the mufflers:
If you took a 12" section of standard exhaust tubing, and struck it with a fork or something, it would resonate at it's natural frequency. It would make probably much the same noise as the above video. Now if you held that pipe, you would dampen that noise and it wouldn't resonate (ring, make noise, etc) at all. Obviously you cannot hold the exhaust while you are driving (for a variety of health and safety reasons) but it is possible to wrap the entire exhaust in heat wrap.
My theory is that this heat wrap will dampen the natural harmonics of the exhaust tubing and allow the exhaust to sound much smoother without the harsh metallic-pipe-being-drummed-on kind of sound. Basically, I'm looking for the *sound* of a short-pipe 13b, like this:
Only far quieter by way of several mufflers, and without the rasp associated with a long exhaust system.
Of course this is just a theory that would have to be tested, so I'm just curious as to whether or not anybody ever has tried this? Mostly so I don't waste my time, energy, and money on something that is invalid.
edit: Also, hot exhaust has more energy than cold exhaust. The heat wrap might have a slight performance benefit if it can keep more energy in the pipe (more energy, more velocity?) instead of disippating it. Probably result in more flames too.
08-23-12, 02:26 PM
#2
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i think you can separate this into two phenomena.
one is the acoustic "pingy" noise, and the second is the insulation part.
to the first, one reason we use the RB stuff is because its thick wall tube, .120" instead of .65" or .40". the pingy effect is actually some kind of resonance of the pipe, and the .120" wall is much better about this than the thinner walled stuff.
the second, the insulation/heat wrap will keep the heat in the pipe, which does a few things. it keeps velocity UP, it keeps the passengers shoes from melting. all of the factory exhaust pieces are thin walled pipe, with a cover, and between the pipe and cover is a layer of some kind of insulation.
the only con for the heat wrap is that the pipe is hotter, so it shortens the life a little, and or can cause a failure. i think the best solution right next to the engine is a heat shield, but further down heat wrap should be fine
one is the acoustic "pingy" noise, and the second is the insulation part.
to the first, one reason we use the RB stuff is because its thick wall tube, .120" instead of .65" or .40". the pingy effect is actually some kind of resonance of the pipe, and the .120" wall is much better about this than the thinner walled stuff.
the second, the insulation/heat wrap will keep the heat in the pipe, which does a few things. it keeps velocity UP, it keeps the passengers shoes from melting. all of the factory exhaust pieces are thin walled pipe, with a cover, and between the pipe and cover is a layer of some kind of insulation.
the only con for the heat wrap is that the pipe is hotter, so it shortens the life a little, and or can cause a failure. i think the best solution right next to the engine is a heat shield, but further down heat wrap should be fine
08-23-12, 10:57 PM
#3
Environmentally-Hostile
Thread Starter
I think I'm going to do it. Shouldn't take more than 2 rolls of wrap I wouldn't think. The 7 is going under the knife for the carb conversion anyways. I'll be sure to post a before and after video to document any changes.
08-29-12, 08:10 PM
#4
Extremely interesting theory and I'm very curious to see how it works out. My 7 will be going into storage soon to avoid the winter and exhaust is my #1 priority. Please update the thread as soon as you have some results, I would greatly appreciate it. Good luck!
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