Resonator sizing (for BRM exhausts or just in general)

[Kinesthesia]

First, let me thank Greg (AZhitman) for developing an exhaust system that allows me to have the options to worry about such things.

Having said that, I assume as with all things, there are diminishing returns on increasing the size of a resonator.

Can anyone tell me or even guess what changes in sound level there is between the 14", 18" and 22" resonators offered by BRM.

Greg mentioned that it would even be possible to add a second resonator. So I consider two 14" resonators, or even two 22" resonators and I have to wonder what this would sound like.

I assume that this all can't be easily quanitified with numbers. It's probably more of an art along the lines of mechanical music...

Maybe I'm wrong and more is just better, and somehow a high flowing exhaust could be created that is more quiet than stock, just through a string of resonators...

[AZhitman]

Definitely playing with the law of diminishing returns.

2 22's won't fit cleanly...

At some point, you have to depart from the idea of straight-through exhaust in the pursuit of quiet. You CAN have both, but one man's quiet is another man's "little too loud".

[Julio Bro!]

Hi Kinesthesia: I like your engineering thinking about the exhaust issue, I've been around those lines for a couple of years.

In theory a string of resonators, at some unknown number, would be quieter than stock. But that's why a stock system is so restrictive initially. Factory systems look for low, pleasant, or no sound, and no vibration. So you have small diameter tubing, a smaller diameter (inside) resonator and a 3 chamber muffler with small tubes inside that usually go through smaller still exhaust tips. Each of this that you "open" will bring a louder sound and vibration to the system.

The measure of this that you're looking for, even though relative, can give a you an idea of what to expect. You'll need a sound pressure meter from...say...Radio Shack, that let's you see how much decibels the system makes outside and inside the car. For example, about 3 years ago I had 2.5" tubing with a Dynomax race muffler which internally had nothing. The droning was terrible and inside the car the sound measured 97 decibels@3000rpm, this is downright sickening. Adding the factory resonator brought the sound down to 91 decibels, still too loud, but tells what the resonator can do.

Now, most strait-thru mufflers give lower decibels than this and with a resonator even less, but I don't have that data yet; try your own investigation and see what comes up. A fact though is that the longer the muffler or resonator, the less sound it will give off.

[Kinesthesia]

Like everyone else, I want my cake and eat it too. I want the least restrictive exhaust imaginable and as quiet as possible.

So, let's break this down a bit.

First, how much difference is there between in volume between a 14" resonator and a 22" resonator ? Not that I expect sound pressure level measurements or anything, but I'd take a vague description.

Secondly, I wonder what benefit might be obtained from two resonators. For example would two 14" resonators be more effective than one (theoretical) 28" resonator ? Is there a benefit that comes from resonator / restriction (resuming stock pipe stize) / resonator over a single resonator of the same total size ? (I'm repeating/rephrasing the same question)

[AZhitman]

Here's some info from our designers / fabricators:

2 14's will not be quieter than a 22". The 22" resonator coupled with our dualtip Magnaflow muffler is about as quiet as you'll get for a straight-through system.

You CAN get quieter, but at the cost of restricting flow.

We have tried to get longer SS resonators, but the internal core of the longer stainless resonators is 2.25. Great for a 2.25" system, but restrictive on a 2.5 or 3".

Hope this helps!

[Kinesthesia]

It clears things up nicely !

Thanks again Greg. You just designed my exhaust... The only remaining questions for me are whether I want the rest of the system (minus the resonator) to be stainless and to go measure my cat.

[Julio Bro!]

Hello Hitman:

A 22" resonator fit's OK? What is the case diameter? Do you have a picture of one installed?

Julio.

[VA240]

Here's some info from our designers / fabricators:

2 14's will not be quieter than a 22". The 22" resonator coupled with our dualtip Magnaflow muffler is about as quiet as you'll get for a straight-through system.

You CAN get quieter, but at the cost of restricting flow.

We have tried to get longer SS resonators, but the internal core of the longer stainless resonators is 2.25. Great for a 2.25" system, but restrictive on a 2.5 or 3".

Hope this helps!

I was just going to suggest the Magnapack resonators, but I realized these are what you are talking about. The link I was looking at mentions they are 2.25" internally.

Arrrrgggghhhh........

-VA240

[AZhitman]

Julio - The 22" fits wonderfully.

I believe the outside dimension is 3.5" (not positive). I will shoot some pics of mine after I instal it this weekend.

VA - One step ahead of ya.

[Julio Bro!]

The 22" measure is the length of the case or overall?

[AZhitman]

22" is the length of the resonator.

Keep in mind it's nothing like the OEM-looking muffler. Thnik of it as looknig like a cherrybomb muffler, where the larger-diameter pipe is 22" in length.