the 10" cherry bomb on my MR2 isn't quite effective enough for my local autox group. They asked me to bring it down (literally) a couple decibels before I bring the car back. So it doesn't need to be MUCH quieter, just a little bit quieter. I really want to keep it compact and light and easy clamp on/off like the current setup. Any ideas?
A couple decibels is almost half. Decibels is logarithmic, going up by ten is actually multiplying the sound level by ten.
As a rotary person, there is no such thing as a small, light, and effective muffler. Effectiveness comes from size.
Also, that oxygen sensor is going to be faked the hell out due to being so close to the tip.
Get a Supertipp. Not a real name, it's what I call it :) Basically, it's a Supertrapp disk stack that you can clamp on to the exhaust tip and decrease the amount of sound by playing with the number of discs. You get to choose between high flow or low noise, but you can fine-tune to suit your needs. I've used one to get my Locost to meet local sound limits.
https://www.summitracing.com/parts/sup-344-1505/overview/
It likely wont be enough but a turn down muffler tip will have a large affect on loudness. Sample:
In reply to Keith Tanner :
I think this may be the perfect solution!
Keith Tanner said:Get a Supertipp. Not a real name, it's what I call it :) Basically, it's a disk stack that you can clamp on to the exhaust tip and decrease the amount of sound by playing with the number of discs. You basically get to choose between high flow or low noise, but you can fine-tune to suit your needs. I've used one to get my Locost to meet local sound limits.
https://www.summitracing.com/parts/sup-344-1505/overview/
Supertrapp muffler for the win! Only other option I can think of is a center inlet/dual outlet perpendicular mount, a la Porsche.
I was trying to find an image of it, but I recall an FD RX-7 that had four mufflers tucked sideways inside the bumper.
Bends are your friend when you are trying to cut noise. If you stuck two 180 bends on the end of that pipe, it would give you more room for a tip as well as kill some of the noise.
RX8 mufflers are single center in, dual outside out and Junkyard cheap! Probably quiet but heavy.
A couple of bike canisters on top of each other aimed to one side? Light, cheap, and cool looking.
Biggest cheapie ebay real muffler aimed towards one of the frame horns is probably the ticket for simplicity and effectiveness.
Totalflow has a bunch of sub $40 prime shipping polished stainless magnaflow type 5x8" or 4x9" canister mufflers to choose from. If you click one you have options for every other size in that style. They are straight through and 11lbs.
A thought that would be interesting to try-use the totalflow 33385 dual 2.25" in/out aimed out towards a frame horn. Loop one outlet to the other and have it run back through the muffler to the other side inlet which you now use a turndown on and aim at the ground. You get twice the effective muffling length in the same size can.
Use Supertrapps on my car they are effective if you don't choke them down too much. Nice thing adjustable by adding or subtracting baffles.
What? Ten posts, no "pick any two" jokes?
Floating Doc said:What? Ten posts, no "pick any two" jokes?
There is no "small, effective" muffler, or "light, effective" muffler 
I guess maybe turbos count? But they aren't exactly bolt ons. And sanctioning bodies tend to frown on you claiming that it is only there as a muffling device.
In reply to Knurled. :
Edit: you edited your post while I was posting.
In reply to EvanB :
To meet the letter of the laws that said all vehicles must have a muffler, Mack put "muffling device" on their turbos.
I needed that when a state trooper busted me for not having a muffler on my mercedes. It's a "rotary muffler."
My 91 Civic STS car had a Burns muffler on it.
https://burnsstainless.com/products/2-stage-mufflers?variant=8112387162203
The car wasn't truly quiet, but came in under the 100db requirement. Thus is what a few autocrossers I know use for higher flow applications. Others choose supertrap.
So pick your poison.
In reply to Lof8 - Andy :
These work for me . Get the "medium sound"
In reply to Lof8 - Andy :
What's wrong with the stock muffler? Ain't no way your making a ton of power in that zz30.
In reply to _ :
Big, bulky and heavy. This is an autox-only vehicle - not even registered for the street. I built it for the $2k challenge and dodging cones. The priority is light weight.
Lof8 - Andy said:In reply to _ :
Big, bulky and heavy. This is an autox-only vehicle - not even registered for the street. I built it for the $2k challenge and dodging cones. The priority is light weight.
If those are the requirements, a supertrapp or similar will be your best bet...
Came here to say Supertrapp. Needed one for my 83 GTi cause I was over the NER autocross limit.
The testing back in the day always showed a supertrapp had to hurt power to be quiet.
You need lots of direction changes and/or lots of length and circumference of packing material. A cheap turbo muffler is probably the lightest and quietist combo.
A thrush hush 17631 or 17632 is a turbo muffler that also has packing. Can be had on Amazon for $32 shipped and weighs 9.15 lbs. Again it would have to turn out towards a frame horn.
Keith Tanner said:Get a Supertipp. Not a real name, it's what I call it :) Basically, it's a Supertrapp disk stack that you can clamp on to the exhaust tip and decrease the amount of sound by playing with the number of discs. You get to choose between high flow or low noise, but you can fine-tune to suit your needs. I've used one to get my Locost to meet local sound limits.
https://www.summitracing.com/parts/sup-344-1505/overview/
Ordered. I'm thinking this is the perfect solution. A hose clamp doesn't seem the right hardware to keep the exhaust pressure from blowing this thing right off the pipe though.
In reply to Lof8 - Andy :
If exhaust pressure is high enough to blow a hose clamp off, the restriction it imposes will outweigh the weight benefits.
You should never see more than 1psi in the exhaust system.
Lof8 - Andy said:Keith Tanner said:Get a Supertipp. Not a real name, it's what I call it :) Basically, it's a Supertrapp disk stack that you can clamp on to the exhaust tip and decrease the amount of sound by playing with the number of discs. You get to choose between high flow or low noise, but you can fine-tune to suit your needs. I've used one to get my Locost to meet local sound limits.
https://www.summitracing.com/parts/sup-344-1505/overview/
Ordered. I'm thinking this is the perfect solution. A hose clamp doesn't seem the right hardware to keep the exhaust pressure from blowing this thing right off the pipe though.
Plus one on the SuperTrapp. Ditch the hose clamp for an exhaust band clamp or do a weld-on.
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