I got popped for a modified exhaust recently. So, I bought a RB Catback hoping to quiet it down to the 95db limit. After installing the RB catback, I measured with a sound meter, and I am still running 94-98db, depending on how I measure.

Any idea on what I can do to quiet it down about another 5db. I have a down pipe, and a mid pipe. no cat or pre cat. Of course I do not want to lose any horsepower to quiet it down. But I realize this may be my only option to keep the police off my ***.

Anyone who has had first hand experience with this have any suggestions?

 

i'd try throwing a resonator somewhere along your catback. that'll quiet it down some and won't take tons of HP away.

 

If your midpipe is not resonated, you will have some sound problems. I've got the Pettit resonated midpipe and its decent below 4500rpm. That's also with an HKS straight through exhaust. I'd think you'd be ok with a resonated midpipe and Racing Beat catback but you may have to double check if you're running nonsequential twins or a single turbo. You'll have more bass to deal with then.

 

You can get a muffler welded into your MP. That shoudl help alot, and if you get a good muffler it won't really hurt your flow. Or if you can't find someone that will do that for you you can goto http://www.vrsexhaust.com/html_tips/dpipes.htm I got mine form them. They use a flow master muffler if I remember right.

 

What does a resonated midpipe do, and how much horsepower loss can I expect?

Am I better off with a high flow cat?

I have also heard of people welding in a borla XR1 into their mid pipe?

anyone that can suggest this?

And yes I am running a single turbo

 

Flow master is not a straight thru design if I remember correctly. I think the Borla XR1 is. anyways, I would think with the right kind of non restrictive muffler welded in could easily drop another 5db.

However, I want to make sure it will work, before I go and throw more cash at the problem.

 

Just wondering where in so. cal did you get popped for a modified exhaust? I wanna avoid that place.

 

If you want to aviod it, move to another state.

 

Get a resonated midpipe. I went from a straight thru midpipe to a resonated one and noticed no power decrease on my butt dyno.

 

Actually the muffled midpipe from VRS Exhaust is a Magnaflow muffler and it is a straight through design. I have it with the RB dual tip and full non-sequential and my car is reasonably quiet unless I floor it. The Borla XR-1 is nice too, but a lot more expensive than the one from VRS after you add in the cost of a midpipe and welding.

 

True, but the Borla has stainless steel packing. In other words, it won't burn out like a cheap-o muffler stuck in the middle of a rotary engine's exhaust path...

After converting to non-sequential, I went through an ASP Racing cat-back (no longer available), a PFS cat-back and finally settled on the RB twin tip, which eliminated the droning and backfiring that was driving me crazy. But it wasn't until I put an XR-1 in the midpipe (I was one of the first to try this, back in '97) that it really knocked the noise down an appreciable amount. I can't take all the credit, since Brian Richards (M2/Mostly Mazda) told me to try it, because that's what they were running on their race cars (three in-line XR-1s).

For reference, with a blown engine (both rotors) I put down 238 RWHP at 10 psi through a Tri-Point downpipe, Tri-Point midpipe with the XR-1, and a stock cat-back (was waiting on the RB at the time). The XR-1 doesn't hurt power at all. And if you're wondering why I bothered to dyno a blown engine, it was because it was a club event and pulling out would have bumped the price up for everyone else.

 

Thanks for the clarification.

I wish there was a way to guage what you mean by "reasonable quiet" Got any sound clips

 

I got blackflagged at Lagune Seca running a full exhaust - dp, mp and RB cat-back. Threw on a Mindtrain pre-silencer (3" at dp/mp connection, splits into 2- 2.5" pipes, 3" at mp/cat-back connection). Sound came down appreciably.

A high-flow cat will cost you about 15 hp. at 13.2 psi boost, I do 337 rwhp with a mp, about 320 with the high-flow cat.

 

****!!! thats a huge amount of power to give up IMHO.

 

I've never dyno'd with the resonated midpipe. I'd assume a loss of about 5 hp, and it's very much quieter.