I blew over 102db at an AutoX yesterday. So I need to add a resonator to my ARTech exhaust. Right now it's a Maxim Works header, and 2.5'' from the collector to the back of the car with one 6'' round Magnaflow at the end. I would like to add one in the middle somewhere, but I need some input on sizing. I measured and the length is not what concerns me, but the width from the transmission/trans tunnel.

Anyone have experience with the Magnaflow "race" mufflers? They seem to be a lot shorter than the standard resonators.

This is my exhaust.



These are the resonators I'm looking into. What should fit there, and bring my car down to the low 90db?

http://www.summitracing.com/parts/MPE-14156/

http://www.summitracing.com/parts/MPE-10416/ (comes in a 14, 18, 20'' length)

 

add the second link muffler as long as you can fit.

 

Yeah, that's the question. As long as it can fit.... lol

I'll get back down there with a measuring tape and try to figure it out. It's just hard to measure for roundness and taking into account any exhaust movement. If I can I want to get the biggest/longest one since I DD this and driving around with ear plugs sucks.

 

I *think* the 18'' body one should fit. I just looked again. I'll give it a go.

 

I was once black flagged in my M3…was about 4 dB over the limit. Fix it or you can't race next time, okay I'll sort it out.

So what I did was measure SPL at home at a constant 3000 RPMs, no load with the meter 10 feet from the exhaust tip. My thought was that if I could get some amount over a 4 dB drop under those conditions, the much louder sound at higher revs and load would also drop by around the same amount.

I added a magnaflow crossover/X pipe resonator and noted that this cut dBs about 5-6 dB's. Encouraging. Primarily it cut the higher frequencies which are what tend to get you at sound limited events due to the fact that they use the A scale (which emphasizes higher frequencies). The car still sounded good and the tone was deep. Some of the dB drop came from the resonator's action, and some possibly from the X-pipe aspect.

Success! At the next event my levels were around 6 dB lower which gave me about 2 dBs to spare.

It's hard to get consistent readings for event sound for a variety of reasons. However the quick and dirty test I did helped me find a solution quickly so that I did not have to worry too much. Had the magnaflow only cut 2 dB then I'd have gone with a large one.

You could also add a larger volume rear muffler if the resonator does not cut the SPL enough.

 

Yeah, well I measured myself before going down with a meter from the side, 50 feet away driving by WOT. The same way my home club measures and I was b/w 96-97. I figured 1-2db wouldn't matter but they measured me at over 100. BUT that was also off the start from behind the car. Next to a building...

In any case, I bought the 18'' body magnaflow and am going to put it in tommorow.

 

That measurement method has way too many variables, no disrespect.

 

Add a turbo to the exhaust. It'll drop the exhaust level by 20dB.

You can "cheat" and get a angled pipe and a clamp so when you show up at the next event, see where the mic is and point the exhaust away using the angled tip. I've seen this done quite a bit.

 

or install a 5x11x24" muffler and enjoy life?

 

Had a guy at my last autox who's exhaust popped 120db, even with the angled tip. So loud I had a ringing in my ears for a while after they booted him.

 

They measured you at 100 even by the building. They said they measured you again after you came in from a run and it was 102. I dont know. Someone also mentioned that when the clouds weren't overhead you were in the 90s but I dont know if I buy any of it.

 

Yeah that's what they told me. Apparently I hopped from 100 - 102 -97 and then back to 101. Seems to me like someone didnt k kw how to use the meter to get consistent readings

 

No I watched him do it, it was completely inconsistent. Oh well, you were definitely the loudest car there and no one knew you so you got picked on. I wasn't happy about it.

 

Pickin' on the Canadian boy....

 

it's too loud. this is good for him. I bet I never hit 90dB.

 

Oh, I know it's too loud. I had plans to quiet it down anyways. This just made me do it sooner.

 

I ran a 12" borla with a resonator.. 3" OD... Long story short the resonator didnt make a difference. I switched to a long muffler and my car is almost as quiet as stock.

 

I run a 5x11x24 "y8spec" muffler on the black car at Laguna - aimed down and left (away from the sound booth) it runs ~85db at WOT.

I think the resonator will get you 4-5db - not 10.

 

(zack morris's phone)

I also have a cat and resonator. Mines softer than y8s for sure

 

A longer tail pipe after the muffler will also lower exhaust note A LOT however i dont know how you can do something like that on a miata without looking like Frankenstein setup.