Variable geometry exhaust system?
10-03-2004, 04:16 PM
#1
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Variable geometry exhaust system?
I want a quiet high flow exhaust.
I've also thought about making a variable geometry exhaust system, to see if it would improve the low speed power of the engine. By it's nature, it should also be quieter at low speeds.
You can look at the following diagram I've made two ways:
~Two pipes, one inside the other
~Three pipes, with two smaller pipes below the main pipe
Mufflers/resonnators would follow in the rear of the car.
Both designs have a throttle on the main pipe, which is closed with engine vacuum. At low engine speeds and part throttle, exhaust flows through the smaller volume piping, at high rpm, and WOT, the valve would be open, and the gas flow would be through the main pipe.
Big pipe exhausts hurt low speed power. Because exhaust gas speed and volume is low, extraction from the cylinders is poor, which leads to a natural EGR effect. As engine speeds increase and gas volume increases, there is enough gas speed to create a vacuum in the cylinder as the gasses escape.
By having two different sized pipes, gas speed could be kept at a constant.
Any ideas on which might be better? Pipe sizing?
~So far I have thought of one problem with the concentric design. With so much surface area, the exhaust will cool too quickly and slow the exhaust down. So the pipe might have to be insulated?
~The three pipe would be heavier.
I've also thought about making a variable geometry exhaust system, to see if it would improve the low speed power of the engine. By it's nature, it should also be quieter at low speeds.
You can look at the following diagram I've made two ways:
~Two pipes, one inside the other
~Three pipes, with two smaller pipes below the main pipe
Mufflers/resonnators would follow in the rear of the car.
Both designs have a throttle on the main pipe, which is closed with engine vacuum. At low engine speeds and part throttle, exhaust flows through the smaller volume piping, at high rpm, and WOT, the valve would be open, and the gas flow would be through the main pipe.
Big pipe exhausts hurt low speed power. Because exhaust gas speed and volume is low, extraction from the cylinders is poor, which leads to a natural EGR effect. As engine speeds increase and gas volume increases, there is enough gas speed to create a vacuum in the cylinder as the gasses escape.
By having two different sized pipes, gas speed could be kept at a constant.
Any ideas on which might be better? Pipe sizing?
~So far I have thought of one problem with the concentric design. With so much surface area, the exhaust will cool too quickly and slow the exhaust down. So the pipe might have to be insulated?
~The three pipe would be heavier.
Last edited by PorKen; 10-04-2004 at 03:28 AM. Reason: Variable volume exhaust system?
10-03-2004, 07:27 PM
#2
I have posted on this topic before, I have a valve to give you variable flow. It operates like many systems on high end cars such as Lambos and Ferrraris.
This vavle works via, increasing backpressure when the performance isn't needed, thus quietning down the exhaust, then it opens to provide extra flow when high flow is needed. I will run this with twin 3 inch pipes on my stroker.
This vavle works via, increasing backpressure when the performance isn't needed, thus quietning down the exhaust, then it opens to provide extra flow when high flow is needed. I will run this with twin 3 inch pipes on my stroker.
10-03-2004, 07:38 PM
#4
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Variable geometry exhaust system
I realized that I made a double-entendre with the title of this post. I meant volume with respect to displacement, not the sound level. But I guess it works for both!
...
Greg Gray,
I remember your posts, and I was going to post that Lambo variable geometry pic as an example. BTW: Your setup sounds like it will be a monster!
I have been thinking and researching and came to the conclusion that it was the size and length of the pipes that mattered, in regards to gas flow.
Smaller diameter pipes promote faster gas speed. A restriction in a larger pipe late in the system might reduce the sound pressure, but won't help with low speed extraction?
...
Greg Gray,
I remember your posts, and I was going to post that Lambo variable geometry pic as an example. BTW: Your setup sounds like it will be a monster!
I have been thinking and researching and came to the conclusion that it was the size and length of the pipes that mattered, in regards to gas flow.
Smaller diameter pipes promote faster gas speed. A restriction in a larger pipe late in the system might reduce the sound pressure, but won't help with low speed extraction?
10-04-2004, 03:08 AM
#7
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N!,
Thanks for the link. You been reading the ricer mags haven't you.
From what I could gather it's spring loaded. I found that a valve which only held closed by spring pressure tended to flutter as pressure built up, then released. If it was engine vacuum operated, it would be slick.
They also have a cable operated exhaust valve (but like the muffler, only on their Japanese site):
...
I'm talking about doing the exhaust pipe, though.
The stock US single pipe is 2.5" ID, so I'm thinking of a 3/4 concentric or 3/1.75/1.75 single/duals or maybe 3/2 single/single.
Thanks for the link. You been reading the ricer mags haven't you.
From what I could gather it's spring loaded. I found that a valve which only held closed by spring pressure tended to flutter as pressure built up, then released. If it was engine vacuum operated, it would be slick.
They also have a cable operated exhaust valve (but like the muffler, only on their Japanese site):
...
I'm talking about doing the exhaust pipe, though.
The stock US single pipe is 2.5" ID, so I'm thinking of a 3/4 concentric or 3/1.75/1.75 single/duals or maybe 3/2 single/single.
