Just picked up a Jackson S/C Miata to run SSM autocross. I need a good guess on the exhaust system requirements. It's a pretty stock internal 1.6 with an M45 supercharger which will be tuned on E85 to maybe 180 rwhp.

The exhaust needs to keep the sound to 93dB at 50'. Not going to buy something all chromy and fancy. I need to get kinda close before I go to the tuner because if I need to make changes to the exhaust, I'll have to redo the tune. I'm thinking in terms of DynoMax bullet mufflers, Ultra-Flo's etc.

So for any supercharged racers out there...what's the minimum exhaust I need to keep this from being an ear-bleeder? Starting with race headers and no cat. Trailer queen -- No street use at all.

 

Hard to say with the blower. The blower car is going to be louder than an N/A car or a turbo car. With my turbo using both lengths of dynomax bullets in 3" diameter and the 3" borla xs pro my car is in the lower to mid 80's for db. But I've got the turbo making it quieter too.

The pretty standard setup that passes nationals sound at your level of power (aka CSP power) is a 2.5" exhaust and a flower master hushpower II mid mounted with an under car dump and super trap plates in case to run events where it needs to be under 90db.

 

Research what makes the most power where you need it in the power band for autocross and add as many larger resonators/mufflers as you can.

 

I'd put on a magnaflow resonator and the largest magnaflow muffler. I remember Brain had some specs on the size that fits. I'd imagine someone will chime in.

 

That largest magnaflow also weighs a ton.

 

I'm thinkin' Dynomax Ultraflow 17222. If there's room for it.

Was recommended by their tech support guy who supports tracks with sound control. I have a pair on a built V8 that worked out well.

 

To be at 93db you are going to have to have a lot larger and heavier muffler than you want. When we went from a turbo to a twin screw, the increase in exhaust db was almost unbelievable. In addition to the tube style muffler we were running that dumped just behind the seats, we've now added a mini cooper sized 2 chamber muffler in the stock location with full tailpiping.

 

You're also making real power.

 

Good input, thanx.

 

I'm running an HKS Hi-Power that came on a turbo parts car I bought that is straight through but surprisingly quiet. Just throwing it out there.

 

Back when I had the m45 on my car at about 190 hp it passed sound at Laguna Seca with stock headers, cat, and Racing Beat Exhaust. That was a normal sound day which was 93 db if I remember right. Every other time I have been there it has been a high db day so dont know what my current setup is. Figure this info will at least give some sort of idea.

 

You could always add a Supertrapp at the end for tracks with lower DB levels.

 

Supertrapps are known for significant back pressure -- at least if you run few enough discs to have much effect on noise. I would worry that it wouldn't work well with up my tune.

My first fall-back is to run an extra 90 elbow at the end which I can aim left or right. Wherever the sound meter isn't. Good for -3dB. But I don't like to be that close, so I'd then add another muffler or resonator and re-tune.

 

I have the full borla spec miata kit on my 130hp n/a 1.8 car. Without the add-on muffler, it's super loud and sounds just like a spec miata inside and outside the car. With the muffler, it barely sounds any different inside the car but my friends say they can barely even hear the car when I'm on track. I haven't ever had it at an event with a sound meter. I only bought the rear section for late Sunday nights after a track weekend when I don't want to **** off the neighbors while unloading the trailer, but it's light enough that I've just been leaving it on the car.

It was more than I wanted to spend at the time, but it ended up being super easy button and I don't regret spending the money. Also note that it has a built-in cat delete.

 

Specs are very loud and not attractive sounding.

 

Build an aluminum exhaust and use 3 vbands to allow you to drop in another muffler if you need it.

aluminum exhaust will be under 10lbs with 3 mufflers.

 

Yes completely accurate. The aluminum exhaust I made that weighed 12 pounds with all 3 mufflers was about 80db. The mid pipe muffler also failed from heat twice on an N/A car running e85. Its still really friggin quiet with both rear mufflers installed. So much Burns packing is in those two rear mufflers, it has like the muffler volume of 6 Burns mufflers, lol.

 

Any details on your aluminum exhaust, and maybe pics of the failure? I am building one for my race build.

you can PM if that works better.

 

I posted most of them in the fab thread I think. Not the failur pics not sure if I took any. But basically it failed because we used 3000 series stainless to make the perf core because it only costs like $60 for a 4x4 sheet rather than $300 for 6061. One fail type it looks like the welds were literally melted off, the other time it failed was because the rivets that hold the 2 halves of the muffler together (so it can be re-packed) failed and pounded the core into the end cap until it broke in half, but that was a design failure. It wasnt able to take the loading from the g forces since the end cap was just sheet metal, the rivets tore out. Made a billet end cap instead and used screws, it didnt fail like that again, the further back mufflers are still running the sheet metal end caps with no problems.

 

Alright, so not the mid pipe, your diy muffler in the midpipe. lol.
awesome.