SimplyKC wrote:We are building a Lincoln Mark VIII for Omaha. The car has cats built into the downpipes/exhaust manfolds. With the exhaust cut off it's really not that loud.
So, if we do some scientific checking, can we go sans mufflers (I understand we will need pipe going behind the driver).
Can the judges check sound level or do they insist that we at least have a glasspack or something on there? It technically does have sound suppresion via the cats that will stay on the car.
I had a Mustang with Borla exhaust on it (no cats) and this isn't any louder than it was. Thanks in advance!
OK you need to understand sound a bit.. Not a lot but enough to stay out of trouble.
First the standard measurement is 92 DB at 50 feet from the track..
IT shouldn't surprise anybody that a car that can run past the metter at 116 db. might be able to pass at 92 bd. without a muffler if a few things are changed..
If the pipes are aimed at the outside of the track they will be louder than if aimed at the inside of the track..
If the car has a megaphone pipe and goes to a straight pipe it will be quieter.
Larger pipes will be quieter than smaller pipes because,... well, you don't need to know (If it's burning you up just ask) Pipes on the outside of the car will be noisier than underneath the car.
V8's with a X pipe will be quieter than straight pipes without one..
Gradual bends do not increase back pressure!
Cast Iron Manifolds vary from great to terrible however the worse the iron manifold is the quieter the exhaust tends to be.. (exception but unless you are a sound geek don't waste your time learning about it)..
An exhaust tip that turns downtowars the ground will be quieter than one that heads straight back..
Finally On a V engine with 2 banks of cylinders if you play around a little you can use the exhaust turn down to do sound cancelling sound .
One will need to be longer than the other and they both should be pointed down and towards each other.
If You know the exact RPM, cam specs and firing order I can give you a calculation but let's face it the exact RPM you're going to be passing the sound meter is going to vary from lap to lap and from track to track.
To summarize, point pipes as far under the chassis (In the middle of the car but behind the driver) the sound has to bounce up and down many times before it gets out and each bounce attenuates sound a little..
The tips should be pointed down and towards each other on a V engine..
One pipe needs to be longer than the other..
Hope it rains! Rain muffles sound beautifully.
There is no rule that says you have to hammer down past the meter! Don't back off completely but feather, almost coast.
Except when passing a car, then if you do it on the inside, away from the meter If the guy running the equipment is fair he knows combined cars will put out more sound than one car by itself..
MY "D" type Jag has magaphones and foot down I record 116 db. at 50 feet.
I can feather it past the meter and squeak by under the 92 db.. (except you could track me all over the rest of the race track) They knew I was noisy but I never recorded more than about 90 BD.. past the meter.
Yes it's cheating and only track officals with a sense of honor and (humor) will let me play that game all weekend.. don't count on it!