Historic Racing and Noise

[turbolarespider]

All of you historic racers- how many of you run at tracks with very restrictive noise requirements?

We are looking to host a national, but our track is very restrictive on noise. I know the cars can be made to be quiet AND fast (see Bernie Martinez) but it would be a significant change from the factory racing exhaust.

Like the last Kwecht GTV- REALLY PAINFULLY loud. But for the Meadowbrook Historic's- they get a waiver for the one weekend.

There are a number of good Alfa race cars in the area that I would like to attempt to get, but hope that we can keep the noise down so we don't get in trouble.

Thanks.
Eric

[conedriver]

Hi Eric,

You must be talking about a 2007 AROC Convention in Detroit, with driving events at Waterford Hills, right?.

Regarding sound control, why not start compiling the sound level restricions at tracks where they currently exist, that way potential entrants who already know their sound measurements will be able to relate to the level you must meet. I know that Waterford has sound control for their road races now, what are the restrictions? (how many decibels at what distance?).

Quote:

Originally Posted by turbolarespider All of you historic racers- how many of you run at tracks with very restrictive noise requirements? We are looking to host a national, but our track is very restrictive on noise. I know the cars can be made to be quiet AND fast (see Bernie Martinez) but it would be a significant change from the factory racing exhaust. Like the last Kwecht GTV- REALLY PAINFULLY loud. But for the Meadowbrook Historic's- they get a waiver for the one weekend. There are a number of good Alfa race cars in the area that I would like to attempt to get, but hope that we can keep the noise down so we don't get in trouble. Thanks. Eric

[turbolarespider]

You guessed right, George.

The rule is 75 dbA at the border, but I know reasonably loud street cars will have no problems. I'm pretty sure your car would be perfect. At least what I remember.

But, to be sure, we are going to measure one loud session of the Italian Happening this fall, so we will know how loud is loud.

What would really be helpful is if a few of you all came up to our track event on Labor Day Saturday. It's a fun Alfa track, mostly 3-4 gear for 105/115 cars. But that would help me tell drivers if they need one or 2 chambers for a normal motor.

[spider4me]

Also which direction is the measuring device from the exhaust may be a critical factor. I understand that several tracks have the measuring device on the inside of the track, so those with side pipes might need more work that those with tail exhaust?

[genericwood]

Eric, my car meets the sound requirements at RA and Blackhawk, even though it has a straight side pipe. I think the limit for SCCA and VSCDA is 102 decibels? The exhaust exits the passenger side of the car because most of the tracks I run measure sound on the left. I will be at Blackhawk this weekend for a VSCDA event. If they post sound, I'll give you more details.

Erik Wood

[Biscione]

Quote from a post listed above:

"For 2005, I installed a three chamber Flowmaster muffler to reduce my sound level for local SCCA autocrosses but don't have a measurement yet. Last year, with the two chamber version it was 98 dB at 100ft. distance measured parallel to the car. The pipe and muffler connections are 2.5 in., and the outlet dumps downward, under the car ahead of the rear axle."

Flowmaster......? Some might even argue that these hollow sardine tin cans with baffles and deflectors do little to reduce sound and do a good job at restricting exhaust gas flow. I will admit that they are probably appealing to the driver of a rotting '71 Chevy pickup with dual rear exhaust and a gun rack in the rear window, but on an Alfa??? Flowmaster uses a reflective sound reduction approach; that is deflecting and rerouting exhaust gases though a restrictive maze. Adsorptive technology uses perforated tubes to achieve better sound adsorption and as an added benefit, will not increase system backpressure. Take a 2.5 inch Magnaflow and run a tennis ball through it; don't try this on a Flowmaster.

Biscione

I do admit I am biased......

[conedriver]

Biscone,

Interesting comments. There is said to be a rotting '71 chevy pickup image for the Flowmaster mufflers. I looked at the Magnaflow website and could be excused for believing their image is a big chrome sardine can tailpipe for the "ricer boy" Asian import with the goofy wings and wretched front air dams.

Let's eliminate both images, and concentrate on performance. I have seen a lot of reference to Magnaflow on the BB, so it is a popular item. Flowmaster is admittedly American-car related, but this isn't necessarily a bad thing. Crossover technology can be good if one can get past a percieved image. You may have heard of Jack Beck, and Orion engineering; many of the components on Jack's very high tech SCCA GT-5 class GTV racer are based on (Gasp!) Sprint car parts. The Orion tubular front sway bar on my car is really the torsion bar from a sprint car and was chosen because it works.

So, rather than condemn a muffler because it has baffles, why not find numerical performance and/or flow values for Magnaflow and Flowmaster. The numbers should eliminate controversy, regardless of which product is best. And... I promise not to call you "ricer boy", if you ignore the gun rack on my Spider (no offense, all in good fun...)

Quote:

Originally Posted by Biscione Quote from a post listed above: "For 2005, I installed a three chamber Flowmaster muffler to reduce my sound level for local SCCA autocrosses but don't have a measurement yet. Last year, with the two chamber version it was 98 dB at 100ft. distance measured parallel to the car. The pipe and muffler connections are 2.5 in., and the outlet dumps downward, under the car ahead of the rear axle." Flowmaster......? Some might even argue that these hollow sardine tin cans with baffles and deflectors do little to reduce sound and do a good job at restricting exhaust gas flow. I will admit that they are probably appealing to the driver of a rotting '71 Chevy pickup with dual rear exhaust and a gun rack in the rear window, but on an Alfa??? Flowmaster uses a reflective sound reduction approach; that is deflecting and rerouting exhaust gases though a restrictive maze. Adsorptive technology uses perforated tubes to achieve better sound adsorption and as an added benefit, will not increase system backpressure. Take a 2.5 inch Magnaflow and run a tennis ball through it; don't try this on a Flowmaster. Biscione I do admit I am biased......

[turbolarespider]

Quote:

Originally Posted by genericwood Eric, my car meets the sound requirements at RA and Blackhawk, even though it has a straight side pipe. I think the limit for SCCA and VSCDA is 102 decibels? The exhaust exits the passenger side of the car because most of the tracks I run measure sound on the left. I will be at Blackhawk this weekend for a VSCDA event. If they post sound, I'll give you more details. Erik Wood

[conedriver]

Eric,

You probably already know that distance is critical in sound level measurement. I was measuring sound levels at a CENDIV Solo II event a few years back, and worked with a guy who provided a spreadsheet formula to calculate sound level degrdation based on distance. I emailed this to you and maybe it will assist with your activities.

I remember from many years ago that Waterford Hills published the locations of their sound control stations and these were on the outside of the track. The organizers then encouraged competitors to use extensions to aim their exhaust away from the sound stations. I'll bet the Waterford racers have a whole new bag of tricks for sound control. And... how far away from the track edge are the sound stations?.

And... you may be using something far more sophisticated, but Radio Shack has a digital sound meter for around $60.00.

Quote:

Originally Posted by turbolarespider Erik From what I am aware of, the SCCA 102 dbA is too loud for this track. I *hope* that only one muffler would be required. But the last I heard your car run (as it passed me on the front straight at Nashville Motor Speedway), it would be too loud. Actually, here's something that is possible- our IH track event is Labor Day Saturday, which we will be taking measurements. PERHAPS, I can bring a measurement device to Watkins Glen the next week to measure some of you guys. (the WG event is new planning for us.... to watch and have fun) I will see, and work on it. Eric

[genericwood]

Eric, that would be great. It would be nice to meet you and Innes (sp?) at Watkins Glen. I would be interested in any performance information that can be provided about various options. I'm sure I will eventually find a weather/track combination that puts me outside the rules.

Erik

[turbolarespider]

George,
You are 100% right- WH has the sound meters at the border. And for the most part, IF you exited the exhaust on the passenger side with one muffler, you would be ok. Anne, the track manager, kind of thinks that the normal SCCA thing will be too lound, but I will also ask some racers that I know about it.

She told me that the 75 dbA measurements are at the property line in 2 locations- one of them is 100ft from the open track, the other is 75ft from a new sound wall. Either way, when you are driving on the outside of the track, you are heading in a CW direction, so drivers side exhuast is not desired.

And really, that is my problem- some of the historic racers in this area (withing a few states) use the correct exhaust, which is essentially a striaght pipe that exits in front of the drivers rear wheel. Of course, that is a simplification, but close enough.

Erik, Ines and I recently stared to talk about coming up, but it will be a short visit- we leave for Spain the week after, so we can't spend either too much money or too much time in New York.

I think we will be there, as we both love seeing GTV's race, and I will take a bunch of pictures for my own Jr's build.

Eric

[sidewaysalfa]

I'll start the right coast talk:
Laguna Seca - 94db measured on the right up a hill at a hard acceleration point. 3 tries to fix the problem and then the track kicks your car out.

On the Alfetta - euro headers, 1 generic muffler and exit out the rear over the axel. Certainly doesn't sound as nice as other exhausts but . . .

[sidewaysalfa]

Dislexia - Calif is on the left coast dummy

[turbolarespider]

As much as I would REALLY love to see some of you left coasters, I can't see you all driving that far for a TT on a small club track, even if Waterford Hills is a fun one. You are MORE than welcome, of course!!!

I digress- how far is that from the track, and is there anything in-between the track and the measurement device?

Your Alfetta is quiet enough, yes? (didn't metion it- but I'm assuming it).

For our track, I'm pretty sure the 100ft has just vegitation between the track and the device, while the 75ft has a brand new sound wall. Very important wall- double layer just to deaden the noise, and the track is but a few feet from it.

Eric

[genericwood]

Eric, I know you are primarily interested in how much noise Alfa racers make. But I thought it might be interesting to some to post the following information from the "unofficial" SCCA production car bulletin board. There has been a good discussion lately regarding sound.

Erik

Here I go again getting technical but it's gotta be said:

2db is huge - it's not 2% increase from 103db to 105db - the scale is logarthmic - that means that 110 is ten times the sound intensity (in watts per meter squared) of 100db In actuality, the sound intensity at 103db is .0199 watts per meter squared and at 105db the sound intensity is .0316 watts/ metersquared so 105db is about 59% more sound intensity than 103db - that's huge.

Second, sound travels at about 343 meters per second in air at 20 dgrees Celcius (that's about 68 degrees farenheit) but it travels at over 5100 meters per second through iron or aluminum. Most of the sound coming out of your exhaust is carried by the metal, not by the exhaust gasses.

Third, sound radiates imnodirectionally - that means that simply turning the tip of your exhaust should do very little but we all know it does something.

Also, sound pressure radiates with the inverse square of the distance. If you get "X" amount of sound at 10 feet, you get 1/4 X at 20 feet (double the distance and you get 1/4 of the sound pressure. A muffler effectively lengthens the distance that the sound travels by causing the sound to bounce around for a while before exiting the system. But the baffles that cause the reflection of the sound can also increase backpressure on your exhaust causing slower intake charge uptake on overlap and thus less power. The trick is in what are called "viscoelastic" materials. These are materials that convert sound energy into heat and dissipate the sound. There are multi-layer coatings that perform "extensional damping" to do that. (hint, hint.) Done properly, you could take some of the restriction out of your exhaust system and still stay quiet.

Lastly, it would be really cool to calculate the wave length of your exhaust note at (pick an rpm, any rpm) and have the main exhaust designed to be that length or a multiple of that length. But then divert half of the output through an additional loop that was .5 times the wave length. Then when the two streams reconverged, the peak of one wave should cancel with the trough of the other wave and the sound would cancel! Can't you imagine the look on the sound guy's face as you came roaring up at 8000rpm and suddenly the sound level dropped 30db! That would be too much fun Basil