How about mazda furai which's got rotary shape muffer?

check it out!

http://www.youtube.com/watch?v=oEOHn7rspsk

belived that's system's suit to12APP, not quite sure about 13B

now that you mention it we put a turbo shaped muffler in our race car, and it dropped the volume, but had to reassemble it after each race....

I am curious to see how long an A-RF style "Swirl Silencer" would last.

They seem to only muffle at full throttle, so it may not be of too much benefit on the street, but for the track it should be stellar. They got a huge drop in noise for less than one horsepower on a 300hp peripheral port.

Yep, I have run my exhaust through a divided turbo without the exhaust wheel in place and it was just at "quiet" as with the exhaust wheel, No exhaust port diffusers, but still no harsh raspy noises like a header produces.



Well, that is exactly like the what Mazdaspeed7 posted https://www.nopistons.com/forums/pub...IR#>/smile.gif

Once you have about 4 complete exhaust pulses in a pipe, there is little to be gained scavenge wise by collecting the two pipes.

It is done just so two mufflers were not needed over one muffler.



So long as the intake has an air filter, the extra sound of the intake will not add much to the sound problem.



The sound meter just measures short cycles of air pressure. Sound is reduced at the square of distance from the source. So,

if there is no distance to the source specified, one wonders what is being measured?



Also sound is poorly transmitted in hot air. It is muted by high humidity. So a car that passes sound on a hot humid Saturday qualifying session, may fail sound on a cool dry Sunday afternoon.



When trying to determin what car is loud and which is not, the ear is just about usless. A car with tonallity deficits may sound harsh or nasty and unplesant to the ear, but be under the sound pressure limit, while your really mellow sounding Rotary may be over the limit. If you are close to the limit on Saturday change the tip direction away from the sound meter, or at the ground. Not quite straight down, but nearly so.

In the padock I insert a big GM street muffler into the tail pipe so as to be a good neighbor.



Lynn E. Hanover



This is 4" ID stainless filled Borla. Makes 102 Db on the worst day. Nice sound.

Hi Lynn,



Interesting your comment on induction noise. As I play around with little cars where the ITBs generally stick out the bonnet, induction noise is a problem. Can't find a picture at the moment, but 10 years or so ago someone raced a lotus7 replica with a PP 13B in it. When it kept winning they tightened the noice regs and it was in fact induction noise that ended up pushing it off the track. The engine was purported to be a little over 300HP at the flywheel, which must have been entertaining in a 1200lb car.

I am suddenly very interested in this topic, as I am being tasked to build a budget drivetrain for a series that has an arbitrary 92db noise limit.

man 92DB is like laguna, stock cars have a hard time with this...

The induction noise is rather easy to deal with if you have the space. Just use two or three paper filter elements inside each other. Only the outer most element must remain intact, to do the filtering. The inner elements may have most of the pleats opened on the inner end with a razor knife, so as not to add to induction drag.



That 92 Db is real quiet.



Lynn E. Hanover