What do you guys think about building a variable flow muffler? I know of a few production cars that have this, the point being that lower rpms would route the exhaust through a smaller diamater pipe and then switch to a larger diamater pipe for better low end torque and better top end while making it quiter untill you get on it.

 

neat idea, but how would it work? pnumatically when the flow exceedes a certan velocity so that it pushes a flapper valve open? electrically via a switch on the tps?

it would be an interesting project, but i don't really think it's feasable, and i think as with E-cutouts that it would prove to have reliability issues.

 

I can think of two ways to actuate it that should be fairly simple:
- Connect it via cable directly to the throttle pedal so it responds to throttle position.
- Advantage - simplicity.
- Disadvantage - gets stuck does your throttle get stuck open?
- Use manifold vacuum with one of those vacuum actuators that are used to control vacuum secondaries on carbs & vacuum advance on older distibutors. The more manifold vacuum the more exhaust restriction.
- Advantage - noise level will be related more to power than throttle position so even if the cops ask you to rev the motor the valve should remain closed & keep noise down.
- Disadvantage - harder to set up & tune so it opens at the right time & probably harder to keep in tune as it's going to be somewhere where it's exposed to harsh conditions.

I doubt you would need to route exhaust through a seperate system, if you put the restriction after the muffler the smaller exit should provide quite a degree of extra sound restriction.
Adding it after the muffler would make design easier due to lower exhaust temps as well.
I've though of doing this with a throttle body but realised that as you are never going to want to close the exhaust off completely you don't need that amount of precision. You could probably fab something up for test purposes fairly easily that would't look pretty but would get the job done.

Hardest part to design would be the bearings that the valve turns on as they will be exposed to heat & water spray/road grit, etc.

Now if you could set the whole thing up inside the muffler... that would be cool!

What gave you the idea? Listening to the Aston Martin V8 Vantage on Top Gear? ;-)
Actually, I think the new Corvette uses this idea as well, I think you can actually see the valves if you look up the tailpipes.




Modified by Surestick at 1:39 PM 5/19/2006

 

The Z06 does this. I'm sure other cars have tried it at some point. Scavenging parts from thier systems will probably be the most reliable way to build what you're talking about. Let the OEM's do the hard part for you
some years of the accord v-6 also has a variable exhaust system.
I'm not sure how or if this would affect your tune, but good luck, sounds like fun.

 

I built this design into my ITR 4" alluminum exhaust. I use an inconel butterfly in the exhaust stream which opens at around 8" HG and stays open in boost. The rest of the time it remains closed which take all the deep anoying noise out of the exhaust.
It's been working 100% for about 8 months so far.

 

My dad has a ferrari F430 which has a similar exhaust system, thats where i got the idea. But i wanted a new sound for my ITR and i was thinking about building a muffler which led to this system. I want to build a muffler with 2 different dimention pipe going through where the valve chooses the more restricted side or the more flowing side. I was thinking of using an old adjustable shift light whith the power to the light hooked up to a relay hooked up to the opening device for the valve.

Thought it wold sond cool, be albe to adust how loud your car is, and adjust when you want a more straight through system.

 

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If you don't want to go crazy yet keep that idea, there's some muffler(s) that might work off the shelf. They're typical 'turbo' baffled/packed mufflers, but the first pref tube runs right up to a blockoff plate. When its removed, it functions as a straight-through muffler. I would guess you could put an e-cutout on it, but since Hondas have the muffler in the rear, it would be more of a noise reducer than a power producer.

Putting a modded e-cutout somewhere upstream would basicly do what you want. Larger exhuast up to the cutout, then tiny tubing after. Would save some weight too. Really depends if it was NA or boost tho.

 

I think you may be over complicating things w/the two exhaust systems ideas. More piping = more weight...
All the info I've read on mufflers indicates that one of the ways to build a quiet muffler is to have the exit smaller than the entrance.
Power-wise a straight through muffler with a valve downstream to vary the size of the exit should work quite well.
HiProfile's idea of modifying a muffler sounds good too.

 

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Power-wise a straight through muffler with a valve downstream to vary the size of the exit should work quite well.
HiProfile's idea of modifying a muffler sounds good too. </TD></TR></TABLE>

Lots of street bikes use this system,

 

just get a jdm dc5 itr muffler, it has a bypass valve built into it

 

apexi has an exhaust with a valve that opens, i dont know if it was over bcause they first made them for the r34's, i dont know the name but saw it at there booth 1.5 years ago.

 

I think the r34 comes with that setup stock.