[Lynn E. Hanover]

1962, on Sep 7 2008, 03:22 AM, said:

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

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.

[bill shurvinton]

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.

[heretic]

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.

[j9fd3s]

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

[Lynn E. Hanover]

heretic, on Sep 22 2008, 06:39 PM, said:

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.

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

[j9fd3s]

ive noticed a couple english cars (jensen healy, and i guess it was an 82 jag xj6) actually have mufflers on the intake. the jag looks particularly weird, as it coned down to a 1" little pipe.

http://www.eap-direc...warrivaleng.jpg

[heretic]

I had a late 70's Ford that had an oil filter on the air cleaner. Weird stuff!

The 92db did sound suspect to me, as the standard of measurement seemed to be to wander around the car with a meter while the driver revved it a little. I am not worried about induction noise since the nature of the race means the stock EFI and airbox will have to be used, no budget for anything "racy". Gotta make power and no money to do it: just my cup of tea. The measurement is from 100 feet at WOT.

At least we can add lightness.

I did have a kind of crazy idea for the muffling. FC chassis. The exhaust pipe(s) would exit into a large volume, like for instance the spare tire well after being suitably sealed, and that volume would have a number of ventholes aimed at the ground. Would it work? Perhaps, perhaps not. I know certainly that the diffusers and the stock exhaust manifold will be in use, which will help tremendously.

quick edit: I was just informed that the exhaust system aft of the manifold/header is free from budgetary restraints. That certainly makes life a lot simpler!

This post has been edited by heretic: 26 September 2008 - 09:11 PM

[j9fd3s]

my last fc was really quiet, all i did was have all the holes fixed in the exhaust. lots of room for mufflers....