Ideas for exhaust muffling for a track day

[M43S7RO]

I tried going out for my first track day about a month ago at AMP (Arizona Motorsport Park) which is conveniently located and I like the layout. Problem is they have a 96db sound cap which I just blew with a 99. I run the BW race pipe with Corsa rear so I knew it was possible I'd be sent home.

Does anyone have any ideas for quieting down a loud exhaust a bit without modifying the exhaust or tips? I'm looking for a temporary solution to take off and be back as I started. Currently searching ideas on the web but most are very temporary for cold start up in the mornings. A solution maybe unrealistic or unsafe for track conditions but thought I'd throw it out there in case someone has been down this road.

Potatoes and bananas in the muffler type solutions come to mind but I would think the added backpressure would be similar to an engine failure I have read of due to clogged cats.

[dparm]

In my old Honda days, they had those "silencers" that screwed into the tip. It was basically just a bottle neck to force exhaust gas to bounce around in the muffler more. Maybe there is a clamp on version or something that only requires a small hole to be drilled on the bottom of the tip?

[SYT_Shadow]

What about switching your muffler for the OEM one? That should quiet it down real good

[derbo]

You should google Laguna pipes , Laguna Seca has a 90dB limit on most days..

They are aimed to the left because the sound booth is on the right side of Turn 5 for Laguna Seca.





https://www.trackspecauto.com/laguna-pipes

[M43S7RO]

Yep, not a fan of switching out exhausts. I find the hangers a pia to swap, getting spare hanger hardware & brackets for an oem muffler would be easier so that I swap everything attached; so this is on the radar.

If I can get a temp solution that I just take off of the tips like DParm says above, that would be ideal.

Originally Posted by SYT_Shadow

What about switching your muffler for the OEM one? That should quiet it down real good

[M43S7RO]

Hmm, maybe a muffler shop could fab something like this for me that would attach over my tips.

Originally Posted by derbo

You should google Laguna pipes , Laguna Seca has a 90dB limit on most days..

They are aimed to the left because the sound booth is on the right side of Turn 5 for Laguna Seca.





https://www.trackspecauto.com/laguna-pipes

[Z K]

I just stuck with the stock exhaust. I can pass Laguna Seca's 90db at WOT any where on the track.

[Davisca455]

Originally Posted by M43S7RO

Hmm, maybe a muffler shop could fab something like this for me that would attach over my tips.

Just another idea, not sure if it would knock enough sound off and still flow enough though.
Maybe your muffler shop can figure out how to add some SuperTrapp disc assemblies to some spare tips?
But they'd have stick out past the paint job.

[roastbeef]

the method of defeating the sound limits is going to depend on how that track measures it. at laguna seca, there is a "sound booth" about 50 yards off the track with a staff member monitoring a decibel reader and reporting cars (car numbers are mandatory for accurate snitching) to the corner workers to promptly black flag you.
they pretend there are sensors all over the track, but this is a fib for deterrence. what you see on that silver gt3 are typical "laguna pipes" that send the sound up and away from the sound booth, and the sound doesn't echo off of the ground. also, the sound booth at laguna is in an uphill section where you'll be at wide open throttle and likely nearing redline.

if your track has a hanging microphone, or multiple areas where they monitor sound, this might not work.

super trapps held on by exhaust springs are an option, but they are expensive to build four (you order as many of those plates you see and build them for your requirements). you're looking at $400+ minimum for super trapps.

another option, buy extra oem exhaust bushings and brackets, and swap to your oem rear section without touching the hangers. its 10 nuts and about 20 minutes.

[sbo76]

One trick on that track is to short shift by the sound checks (I believe there are two of them). A buddy of mine also bolted in an apparatus with steel wool into his pipes (he has a factory five cobra) that allowed him to pass sound. Amp is a cool track - I think I am going out there on the 29th with pro auto if you are around say hello.

[dparm]

Originally Posted by roastbeef

another option, buy extra oem exhaust bushings and brackets, and swap to your oem rear section without touching the hangers. its 10 nuts and about 20 minutes.

I agree this is probably the simplest option. Just swap to the OEM rear mufflers whenever you need to hit up a track with sound limits. It will probably take you more time to get the car up on jack stands than it will to swap the axleback.

[SAMM3Y]

Have you ever seen the corvette guys who build a half pipe over the back of the car and seal it at the end opposite the sound booth? Not an easy solution at all but OP said without touching the exhaust. Be tough to do on an e9x without creating drag too...

[roastbeef]

Well, you wouldn't have to modify it... you'd use some exhaust springs and drill a tiny hole for them to hook onto at the base of the tips.

[M43S7RO]

Thanks everyone for the ideas, I found a local member on the forum with an oem exhaust for sale. Gonna pick that up and swap that in. I would like to find someone with extra hanging hardware and bushings laying around though so that all I have to do is bolt up, swapping the rubber bushings was a pia from what I recall.

Scheduled track day 2/13 with the local BMW/PCA clubs.

[M3 Number 86]

Originally Posted by Davisca455

Just another idea, not sure if it would knock enough sound off and still flow enough though.
Maybe your muffler shop can figure out how to add some SuperTrapp disc assemblies to some spare tips?
But they'd have stick out past the paint job.

Does that thing mess with back pressure and horsepower?

[dparm]

Originally Posted by M3 Number 86

Does that thing mess with back pressure and horsepower?

It is a restriction, so yes, expect a small power loss. I doubt your butt dyno will notice.

[M3 Number 86]

Originally Posted by dparm

It is a restriction, so yes, expect a small power loss. I doubt your butt dyno will notice.

I just saw that it only posted the laguna pipes but was talking about that cap type of thing.

Reason I asked is I dynod a valves exhaust and it was a 40whp differential. Aka less than stock?! Lol

[Davisca455]

Originally Posted by M3 Number 86

Does that thing mess with back pressure and horsepower?

Like most questions, the answer is "It Depends".
The more discs you have, the more it flows, but the louder it is.
Fewer discs, reduces flow, but the quieter it becomes.
I know it looks like a cork, but you can actually stack enough discs onto the assembly to equal the flow of a straight thru pipe diameter (the gap between each disc is tapered so there is some effect on velocity that isn't really apparent to the naked eye)
So if you check the flow of a 2" diameter straight pipe with a manometer, you can then add discs to equal the flow of the open pipe, and the assembly will be measurably quieter, because the 360 degrees of exhaust diffusion reduces the noise that a sound meter would read.
However, there are flow limitations within each disc diameter family, for instance, the 3" disc family will only flow up to a certain point no matter how many discs you install.
In that instance, you'd move up to the 4" family of discs, and eventually you may need to move up to the 5" family.
The 3" disc family was designed for smaller engines.
The 4" disc family was used on larger displacement motorcycles and some cars.
Examples for the 4" disc for motorcycles would be 750cc V-Twins (100ish HP) used in AMA Class C Dirt trackers.
Each cylinder had a 1-3/4" OD headpipe that connected to a reverse cone megaphone that finished with a 2-3/4" ID exit with 35-38 discs stacked on the end.
The AMA Superbikes (1000cc back in the day) would typically have 4 headpipes of 1-1/2" OD that fed into a 2-1/2" OD tail pipe capped off with a glass pack muffler with 35-38 discs.
The 5" disc family was designed for larger engines and was used by some sprint car teams. One set of 5" discs onto each header collector.