What did you do to your racecar to meet your local track sound limit. I have been warned and not sure what else I can do since its a PP with 2.5in headers to a 3in overall down the side of the car for flat bottom.

 

add muffler! also there is a lot of noise from the intake, so an airbox can help

 

I am with a same struggle, it has been a while but I think I am at the edge.

Made a new rear muffler because I thought the old one was worn out, but I was wrong.
Been trying some small thing with no succes.

There are 2 things I am considering to try out though.
A muffler that has a sollid pipe goin trough, and only the last section is perforated. It is something I have seen on a titanium HKS exhaust, i am unsure if it is packed or not.
A muffler where the perforated tube is .25" or .5" smaller.

It now is 3" front to back.

 

A previously 20b PP here, in LHD form, ran the pipes inside the car into a fabbed muffler in an enclosed cf box in the passenger area - which may or may not comply with your rules. The area was packed with foundry insulation and exhausted out the sill under the B pillar.

Needless to say, you needed to pay attention to exhaust leaks.

Long since been made uncompetitive, but in the old days where they used to rule, full length exhaust, resonators under the car and a truck muffler running the full width of the car with a turned down tip - reversed if need be to point away from the meter.

 

I made an elbow out of some piping to aim the exhaust away from the sound booth. It bolts on and off. Laguna Seca is infamous for 90db track days and even less than that sometimes..

This guy knows the struggle
https://www.corvetteforum.com/forums...oadcourse.html

 

Here is a photo of the exhaust. I have thought about it over night and might use some of that flex exhaust tube diesels use to attach 2 more bullet mufflers going towards the front of the car. Build a stand off that allows the exhaust to be installed with hose clamps.

 

A hemholtz resonator might help and it wont reduce any flow. You would have to get a meter to see where its loudest and what frequency but it can be calculated.

 

To my understanding they reduce drone.

I have used branch resonators successfully for that same reason

 

whatever you do, don’t put supertrapp diffusers on the pipe end like in that Vette link

they either kill power or do nothing for sound on a rotary, found out the hard way long ago, PP would be even worse
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i found two things with mine:

1 is that the airbox makes a huge difference. when i fired it up without it the neighbor came out of his house holding his head...
and 2, i have this resonated tip, it looks like the ANSA tips you'd see on an old Ferrari or something, but clamping it on the 3" pipe really kills the noise, it goes from PP to like a stockish car.

 

Fit as much muffler as you can first, then start chasing small incremental gains. I found a downturn was worth just under a dB on average, not enough to cover the difference between a hot and cold day.

This setup came in at ~96/97 dB, quieter than stock GT3s but still too loud for the local track:

Adding a small third muffler got it down close enough to 95 that I ran without issue at the last event. I was worried about the BOV noise triggering the meter but apparently that hasn't been an issue. My next idea was to turn the boost up, I figure the less exhaust bypassing the turbo, the quieter the car should get :p

 

^^ it’s an NA PP engine, not turbo


just stumbled across your youboob channel

how much straight length do you have available on the side pipe? I might have something for you to test.
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Whoops, can't believe I missed that! I have nothing of value to add then, I've never heard a PP that would pass sound at a track that enforces dB limits.

Not sure what you mean by side pipe? On the section between the midpipe muffler and first rear muffler I have maybe 2' of straight length but 0 tolerance for an increase in diameter.

 

It's about 36" of straight pipe from the 90 out from the fender well to the start of the turn down tip.

I have also found that Borla makes a rotary specific bullet muffler. The issue I have is the cut out along the door sill can only accommodate a 4" in diameter muffler and Borlas one that I linked below is 6.25. I could possibly cut some reliefs but I am open to other options as well.

https://proshop.summitracing.com/parts/bor-400373

 

good Borla pricing here, be sure to use a multi-core version

https://ss-exhaust.com

I have an insert that needs a 4” tube to fit/bolt into. I think it’s 24” long, but need to confirm. So that length plus the cone ends if you want to buy some cheap steel tube and try it before spending a lot of money.

lmk
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can you post a photo of what you are talking about. that would save me a ton of headache and not have to trim the skirts up more than I already have.

 

oh ye of little faith; everyone else offers lip service, but you doubt the person offering substance at his own effort and cost.

Turns out it’s 30” long rather than 24” though. So probably 36” long with 3” OD end cones, and the body will be 4.00” - 4.13” OD enclosed. If you think you can fit it I’ll even enclose & cap it at my own expense with no obligation, just for you to test it.

or go spend hundreds without any guarantee that whatever you choose is sufficient either.
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I have faith lol I was just trying to understand what exactly you were talking about. I'm always will to try anything from a small shop or person before "name brand." They typically copy others without understanding or knowing the secret sauce.

 

Let me know when you could ship it.

 

glad you thought about it some more, will send you a pm
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waiting to here back from you on my last pm to finish this out.
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I have the largest 2 stage muffler I could get from Burns Stainless at the time.
It was necessary to add in a 15" Borla straight through muffler to get the noise down further.

As weather conditions can affect sound readings, I also have a 1.5" shorty muffler with turndown that clamps on to the tailpipe if needed.

Have not had issues with sound since then.

1993 Single Turbo, 3.5" exhaust

 

again, it’s a normally aspirated full-on peripheral intake port racing engine. In no way does it even come close to the sound control requirement of a turbo engine configuration. The peripheral port engine is extremely sensitive to backpressure and the sound level is much, much louder and sharper too.
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