learn me race car exhaust

I have a modified BMW 2002. Right now the exhaust is headers into a 2.25" straight pipes exiting the back. Its a bit loud. I'd like to be able to move this thing around and take it to some autocrosses without pissing people off. Ultimately it will need to meet track decibel requirements, but I'm pretty sure I can meet most of those with the open exhaust and some clever exiting of the exhaust away from the sound control station. Behind the rear axle and next to the fuel cell is enough room to run a round glass pack or supertrapp style muffler. Whats out there? What can I expect in the way of sound deadening and performance drop. Right now I'm leaning towards a $100 Stainless glass pack which may not suffice, or a stainless Supertrapp at around $240.

I've never heard anything good about supertrapps. Glasspacks will help some, buy the longest ones that will fit. It will still be loud with glass packs, but they do help take the edge off of the obnoxiousness.

A glasspack with stainless-strip packing will cut down sound a good bit. One step up from a glasspack in terms of restriction is an auger-style muffler, those cut a lot of noise and aren't too restrictive.

Don't bother with the supertrapp.

Get yourself a decent Dynomax UltraFlo (or any of the straight through style solutions they sell) from Summit/Jegs/etc. and a 90 degree turn down clamped to the end to help aim/disperse the noise.

http://www.dynomax.com/mufflers/ultra-flo-welded-mufflers

Note: any of the fiberglass or stainless steel packed mufflers will eventually need their packing replaced. Fiberglass will fail more quickly.

Personally, I'd say that you won't lose much by going to a "super turbo" style chambered muffler and it will reduce the noise quite a bit more without needing to add a bunch of glasspacks/weight, but then more and more I'm finding I don't enjoy overly loud cars (love the noise, just not the volume per se).

I don't know that much about race mufflers, but it has been reported that they won't restrict power much, if at all, and that having a turn down tip will also cut the sound quite a bit.

Burns Stainless has a reputation for building nice, light stuff that makes sound requirements, but it's not cheap.

I have a Dynomax Ultraflo, it cuts the sound a good bit but I get some ricey buzz on acceleration, the muffler shop said the light amount of packing in it is the cause. I'm using it with a louvered SS-packed resonator.

Funny to hear the negatives about Supertrapps. I wonder what it's based on, as it is still the only true tune-able muffler out there. I used to work for a sister company of theirs, and they sponsored my race car for a couple years. As such, I had frequent access to their chassis dyno. I'd tell you all what I found out, but you wouldn't believe me anyway...

tr8todd wrote: Ultimately it will need to meet track decibel requirements, but I'm pretty sure I can meet most of those with the open exhaust and some clever exiting of the exhaust away from the sound control station.

one thing to keep in mind … the reason for sound restrictions is to appease the neighborhood …

keeping the sound to reasonable limits helps keep sites … by circumventing the sound restrictions with turn downs/turn aways … all you're doing is upping the chance the club could lose the site … just because you're not setting the meter off, doesn't mean that the sound isn't going to cause complaints

bravenrace wrote: I had frequent access to their chassis dyno. I'd tell you all what I found out, but you wouldn't believe me anyway...

Tease!

In reply to wbjones:

Chances are those same people would still complain if everyone there was racing Nissan Leafs......

I used to race at Waterford Hills, where they have some pretty rigid sound requirements. I ran a Flowmaster. I was easily below the limit and there's no packing in it to break down.

From what I understand, the issue with SuperTrapps was simply that in order to not lose power you have to run so many discs that there wasn't much help in the noise arena. If you look at the design you can see how that might be an issue.

If you have any data to add to this discussion, we'd love to hear/see it.

The sound control comment was more to give an indication of how loud the car is at present and not an attempt to circumvent the rules, or else I wouldn't be looking for muffler suggestions. I've had cars that failed in practice, then passed with decibels to spare once the exhaust was turned down. Not only does the sound meter read lower, but the car does sound quieter after the exhaust bounces off a few things. Tracks are getting more restrictive since the last time I ran, so I'm sure I will need a muffler for anything other than actual door to door races. FWIW, the TR8 never failed anywhere with open exhaust, but I slid on a set of cheapo Monzas dual tips to go autocrossing and to move the car around at the house. Looking for something similar for the 02. Funny story about the fiberglass packing... One day my Mother in law called saying she thinks she hit an animal and it was sucked into the engine because there was long strands of fur coming out the tail pipe and the engine was louder.

Lobaks AKA Moroso Spiral Flows. Nothing to blow out and decent db drop.

A turbo reduces noise... Just sayin'. ;-)

not particularly cheap, but I like spintech mufflers

I would love to see a write up on supertrapps. EVERY time I see someone use them in a build; they always seem to be most disappointed. Its possible the happy people don't post.

I like the thrush/walker glasspacks(they flow best, straight through perforated tube design), or the thrush/walker "turbo muffler" which is a standard 3 tube type muffler without any packing. The two are also conveniently the cheapest units on the shelf. Never heard a blowmaster chamber muffler that I liked.

bravenrace wrote: Funny to hear the negatives about Supertrapps. I wonder what it's based on, as it is still the only true tune-able muffler out there. I'd tell you all what I found out, but you wouldn't believe me anyway... Please do tell as I have little room to work with and have considered the Supertrapp tips that can be added at the end of a exhaust system

bravenrace wrote: Funny to hear the negatives about Supertrapps. I wonder what it's based on, as it is still the only true tune-able muffler out there. I used to work for a sister company of theirs, and they sponsored my race car for a couple years. As such, I had frequent access to their chassis dyno. I'd tell you all what I found out, but you wouldn't believe me anyway...

I had one on Kimini, my Honda-powered mid-engine Mini. At Laguna Seca, I had to remove all but two baffles to pass the sound test, and the resulting back pressure pushed the end plate out, losing some of its stuffing. The bolts also chose that day to break the internal nuts free so that it was impossible to disassemble it (and yes, the bolts ALWAYS had antiseize on them). SuperTrapp will never have another product on anything I build. I use a Dynomax unit on Midlana and it works great (of course the turbo helps as well :).

tr8todd wrote: Funny story about the fiberglass packing... One day my Mother in law called saying she thinks she hit an animal and it was sucked into the engine because there was long strands of fur coming out the tail pipe and the engine was louder.

My coworkers are now wondering why I'm giggling over here.

We run 3" straight back with one of these dudes in the pipe on our LeChump E30.

It's loud, but a lot quieter than it was with just the open pipe, and it's passes every track we've been to.

bravenrace wrote: Funny to hear the negatives about Supertrapps. I wonder what it's based on, as it is still the only true tune-able muffler out there. I used to work for a sister company of theirs, and they sponsored my race car for a couple years. As such, I had frequent access to their chassis dyno. I'd tell you all what I found out, but you wouldn't believe me anyway...

David Vizard is not a fan. On his testing, he decided a Supertrapp will get you either get high power and high noise, or low power and low noise.

I've got Dynatech Vortex Cones in the exhaust of the LS1-powered MG along with a couple of good packed mufflers. It's very quiet from outside.

Idea, make a ghetto supertrap by using a thrush type glass pack as the last section of exhaust and shove an auger type muffler in there, then clamp on your turndown to hold it in there. Different auger lengths give different volume. Probably flows better than a supertrap too.