Noise: or, put a muffler on that thing, buddy. (Page 1 of 3)

Where's the LIKE button?

We're running a cheapo Magnaflow/Thrush/CherryBomb turbo muffler on the Z and  I wish more people did the same.  You don't lose any power, they're wicked cheap, and available in all sizes.

We run a cheap Thrush as well.  28 bucks.

There are sound meter apps for smart phones. Anyone know if they are accurate enough to keep people out of trouble?

We tested our cars with the smart phone app, at like 20 feet, and it was close enough that we havent been talked to. We were well under the mark at 50'

Damn,  that's Laguna Seca quite ..

Better dig up the stock mufflers, I have yet to find an aftermarket one that will pass there!

Ultimately, db levels measure the energy in the sound pressure of the exhaust note. Sound testing on a cold or rainy day will read at higher levels than on hot dry days. Cool/moist air is more dense, so it better transfers the energy to the dB meter.

One of the reasons that the rotaries don't trip the meter is they shriek. Loud 4 cylinder cars tend to have higher pitched exhaust  as well. Big 6- and 8-cylinder cars will have lower pitched exhaust. These "bass" tones carry farther with more energy than the high freq. tones of 4-cylinders and rotaries.

CA Vehicle Code limits "competition off-highway vehicles" to 96dB and 101dB depending upon date of manufacture. That measurement is taken from 20 inches, and certain rpm that the CVC doesn't specify other than listing an SAE test procedure number. 

92 dB at 50 feet means the exhaust will be a lot louder at the car. I do, however, feel that 92dB at 50 feet is a bit restrictive for a race car, especially a V8 at full throttle.

So, the fix:
4-cylinder with bullet muffler and 2 inch exhaust or less
6- and 8-cylinders with bullet muffs and dual 2.5 inch or less

Any larger diameter exhaust tubing and you'll probably need more muffler.

I was running 3.4L V8 with 3.5 inch single exhaust with a 20"  bullet muffler and that was measured 104 dB at Thunderhill's monitor. I did have a lot of other racer's compliment me on the sound of the car, however.

Lastly, I ran afoul of tech by dumping my exhaust under the car, but in front of the fuel tank at Thunderhill. The current rule set says this is OK, but expect to see that changed next year, and for the rest of this year. So, we spent 3 hours fabbing additional exhaust for a side exit thought the cab and out the right rear passenger door. (We have ground clearance issues) Thanks to everyone that donated tubing and flex and welders. Of course, after all that work, we ended-up too loud and black flagged.

Can you elaborate on that? We have dual exhaust dumped before the rear axle, and a cell behind the rear axle. Its passed tech this was several times, but Id very much not like to be trying to figure out a fix just hours before the start of the houston race.

Two reality checks:

1) If we have to stop talking at the Thunderhill Grill while you fly by into turn 1, you're too loud.

2) If I can't hear my engine AT ALL over your car near me on track, you're too loud.

Oddly enough, one of my favorite things about going to the (real) races is the sound of the cars... except a Lemons race. With a few small exceptions, all of our cars sound like shit and are best kept well muffled.

Neal, we did break.
Killed another engine.
We woulda fixed the sound issue and continued to race,
but for whatever reason a head gasket let go when my driver shut off the engine at the Penalty Box.
Turned out to be a very harsh penalty. We were all pretty bummed.

That's what really sucks about sound energy - I tune for bass which gets hammered at the dB meter, but the screaming rotaries (which I like BTW) get a pass
because of the higher freqs.      Oh, well.

I might agree with that, though 3 seconds of no talking every 2:38 might be nice.
Seriously, was that the 131 Skunk SHO that caused y'all to pause and take a breath? Or some other POS with ratty sounding, excessively loud exhaust?

All of our drivers found the through-the-door-side-exiting-3.5"-awesomeness quite useful when passing on the left.

I ALWAYS strive to be exceptional AND Nobody refers to me as "small."

Hey Greg   so with our tailpipe cut on the mazda we all got Carbon monoxide sickness from pipe not tall enough ..

OOPS  know that for next time.