The 24 Hours of Lemons Forums → Lemons Tech → Exhaust and tech...do the judges bring a decbel meter?
there are decibel measurement apps for iPhones these days, so i wouldn't expect to get away with anything. better safe than sorry.
SimplyKC wrote:Trevor57 wrote:How much power could you make with all that extra noise? I would bet it's not worth it for an endurance car.
I wouldn't expect any extra power. There is even a chance that some lowend torque could be lost witha lack of some back pressure.
Show me a car with backpressure, and I'll show you a crappy car. Engines have never worked that way, its an ancient backyard moron myth that backpressure does all sorts of magical things like prevent exhaust valves burning, raises torque, etc. Any type of Pump (engines here) certainly don't have outlet backpressure to increase anything but exhaust temperature and lower flowrates. If an exhaust has in-built tuning with primary length/collector/secondary/etc, then yes messing with the math could affect torque. A stock engine with cast iron manifolds, don't even think about it.
Lowering volumetric efficiency does nothing but lower power, regardless of how you do it.
Ah Ha! my chance to chime with an obscure bit of trivia.
4 cylinder, 8 cylinder and V6 engines all have improved exhaust flow with a set of headers..
The reason is the odd firing pulse that occurs every 90 degrees.. (I'll prbably screw this up) in a V8 for example 2 cylinders 90 degrees apart fire. then it's 180 degrees before another fire and that pulsing is what gives a V8 it's rumble. With V12 because of the perfect balance design they have, well it's like four 3 cylinder cars hooked to the same crankshaft. Each piston fires 120 degrees apart. Log manifolds don't hurt a V12. since each pulse is 120 seperated.. Run 1 pipe from each header (4 pipes total) That's why when you hear a V12 exaust at idle it sounds like it's turning 1500 rpm but the tach tells you it's only 600 rpm
That rumble is what makes noise!
Clever pipe lengths (60Degree seperated) will put a pulse out to cancel the other pulses. Add a turn down pipe at the end and start the sound absorbtion bouncing under the chassis (behind the driver) turn the downturn pipes away from the outside of the track and in nearly every case I've seen be well under the 92 BD rating at 50 feet..
Exceptions!
Hemi engines..
Because of the fact that much fuel actaully flows outside the exhaust value (during the intake stroke during overlap)in the hemi engine design. (Jaguar 6 cylinder,Offenhauser, some Toyotas, etc) Hemi's will reburn that gas and the added noise needs extra muffling to conform.
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!
An exhaust tip that turns downtowars the ground will be quieter than one that heads straight back..
We cut half the mufflers off our Jag (single exhaust splits then goes through two mufflers on EACH side) and put turn-downs slanted slightly inward - more to keep the exhaust off the diff-mounted brakes than to cut down on noise. When our car was on the track nobody could hear it, but inside the car it was pretty loud.
There were some loud cars at our races.
Then again, the local track sound limit levels are 103DbA.
KT
An exhaust tip that turns downtowars the ground will be quieter than one that heads straight back..
We cut half the mufflers off our Jag (single exhaust splits then goes through two mufflers on EACH side) and put turn-downs slanted slightly inward - more to keep the exhaust off the diff-mounted brakes than to cut down on noise. When our car was on the track nobody could hear it, but inside the car it was pretty loud.
Your car seemed pretty quiet to me at Omaha. Our firebird seemed a bit loud in cockpit, but from the stands, you couldn't hear the slightest exhaust sound. Maybe it was a bit louder in a car next to us.
Our supercharger whine is louder than the exhaust.
http://www.youtube.com/watch?v=jbvp4jMBjbI
http://www.youtube.com/watch?v=1aD5zX1GJLE
An exhaust tip that turns downtowars the ground will be quieter than one that heads straight back..
We cut half the mufflers off our Jag (single exhaust splits then goes through two mufflers on EACH side) and put turn-downs slanted slightly inward - more to keep the exhaust off the diff-mounted brakes than to cut down on noise. When our car was on the track nobody could hear it, but inside the car it was pretty loud.
The V12 has two exhaust manifolds per side (4 total) and right under them a y pipe.From there to the cats.. The power can be gained by using seperate pipes (about 2 inches max 2.5 inches) right from the manifold clear back under the driver but before the differantal. Then join together in a Y and dumped on the ground with a turn down..
Joining them together will net you another 12 Horspower over 4 individual pipes.. Remember that the passenger sides is about 1.5 inches ahead of the drivers side so if you make the drivers side about 1.5 inches longer than the passenger side that 3 inch differance should put the exhaust 180 out of phase and use sound to muffle sound..
IF it's too noisy inside and you still aren't tripping the sound meter you can run them like lake pipes and simply remember to use the down turns to quiet things enough.. IF that trips the meter then run both pipes out the passenger side with down turns
If You have unlimited money buy the stainless steel set-up out of England but a muffler shop will do just fine.. (Me I'm so cheap I'll crawl under with any reasonable used pipe I can get my hands on and weld it all together)..
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