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I would really like to put side-pipes on my 63 coupe build, but the problem I have is they need to comply with our local regulations. The noise level needs be 92 db or less, this is similar to what modern cars noise levels need to comply with. I am running a stock 430hp LS3 with catalytic converters ( again to comply with regs.) I was thinking of running two 2.5'' 24'' glass pack mufflers on each side, I believe these will fit behind the C2 aluminum side exhaust covers? I can't find any examples of this, anyone have any ideas if this would work or some other means of achieving this kind of noise level? Other than an under car system.
92dB is a tough standard to meet. At some track events with my vintage racer (see avatar), my car has had to comply with a 92 dB limit (measured 50' from the track edge).
I tried glass pack mufflers for a while and gave up on them. They made the sound more harsh without lessening its amplitude.
The most effective muffler has turned out to be a set of spiral baffle inserts from Spiral Turbo Specialties:
At events with less restrictive sound limits, I run with 4 baffles (or "flights" as Jim, owner of STS, calls them). For 92dB events, I add 3 more for a total of 7.
This, BTW, is all stuffed inside 3" ID pipes. Strangely, it seems that larger pipe ID results in lower sound level. So you might go with the largest pipes which will fit under your covers.
Now there is one other trick I and other racers use to comply with the sound police: Turn the outlet down towards the ground. It doesn't do much good to stifle the exhaust if you are still blowing it towards the microphone. Seriously. The noise created just by rushing exhaust air can easily exceed 92dB.
I can't help you with your question but I'm curious if the 92dB requirement where you live in Australia applies to all vehicles or just ones that have been modified. If you owned a stock '67 big block that came from the factory with sidepipes would you be required to quiet it down to 92 or would it be exempted since it's original?
It has been done. Here's a photo of my car when I first got it and was stripping it for repair and painting. If you decide to do this make sure that the mufflers are welded in straight. Mine were not and they burned up the insulator for the side pipe covers. I do not remember how loud the mufflers were but they certainly did not have the same mellowness of the original side pipes from GM.
Thanks for the replies, I have heard of the spiral inserts might have to try them.
The 92db limit does not apply to mostly original cars, in my case an extensively modified car i.e. non OEM chassis, engine etc put it into another category and basically I have to comply with the same standards as a new car, emissions, noise, etc. etc. You guys in the states don't know how good you have when it comes to modified cars.
I got all keen on this a while back and looked into Helmholtz resonators.
I modeled it up in my CAD program and this is sorta what it looked like - unfinished!!
From memory the length of the dead end tube was 1/2 length of exhaust valve to exit point of side exhaust (1/2 wave). Tube diameter for resonator section is 2", with a sliding end to tune for best frequency.
If you do a search on google 'Helmholtz resonator' you should have plenty to read.
There is also a version that is 1/4 wave resonator, commonly seen an alot of BMW exhausts,
generally just a J-Tube ~ a piece of tubing bent like a 'J' that welds into the exhaust and is capped at the end.
A true Helmholtz is aimed at 1/2 wave cancellation and therefore requires more volume and a chamber (or multiple chambers) to cancel different waves and attenuate sound at different frequencies.
I modeled it to fit into the crossmember tube where the standard exhaust passes thru at the gearbox mount area. I did not get up to sorting out a mount arrangement. I must finish this..... ! as I'm slowly going deaf with the side pipes!
Neville
Last edited by Nev Williams; 09-23-2016 at 02:54 AM.
The resonator is an interesting concept. And no doubt that it works or BMW wouldn't use it.
But half-wave or quarter-wave, it is a resonant length at only one engine speed. Therefore it will provide noise cancellation over a relatively narrow range of engine RPM.
So what engine RPM are you targeting for noise reduction? And how do you know how long to make the resonator to accomplish this?
The resonator is an interesting concept. And no doubt that it works or BMW wouldn't use it.
But half-wave or quarter-wave, it is a resonant length at only one engine speed. Therefore it will provide noise cancellation over a relatively narrow range of engine RPM.
So what engine RPM are you targeting for noise reduction? And how do you know how long to make the resonator to accomplish this?
Are the catalytic converters right by the engine? How will you route the tubes from the converters to the side pipes?
I love side pipes (have them on mine), but you might find that it is not worth the troubles of routing the exhaust to get back up to the side pipe cover with an S bend or something like that. If you can make a straight shot, then I think the spiral baffles is the way to tune it.
You may not need as many baffles with the catalytic converters.
Thanks for the replies, I have heard of the spiral inserts might have to try them.
The 92db limit does not apply to mostly original cars, in my case an extensively modified car i.e. non OEM chassis, engine etc put it into another category and basically I have to comply with the same standards as a new car, emissions, noise, etc. etc. You guys in the states don't know how good you have when it comes to modified cars.
Are you allowed to use cutouts ? maybe you could have 2 paths, one with a full muffler setup and subtle rear dumper exit, then cutout to the sidepipes at the flick of a switch ?
I run modified HSV bimodals on mine (all exits at rear), quiet is very quiet and loud is almost straight through !
The resonator is an interesting concept. And no doubt that it works or BMW wouldn't use it.
But half-wave or quarter-wave, it is a resonant length at only one engine speed. Therefore it will provide noise cancellation over a relatively narrow range of engine RPM.
So what engine RPM are you targeting for noise reduction? And how do you know how long to make the resonator to accomplish this?
Expiring minds want to know....
Jim
Hi Jim, Your mind cannot be expiring driving a car like that !!
Your exactly right. From what I've read it is not a one size fixes all. The Helmholz resonator only targets specific resonant frequencies. For a drone at say 1800rpm, there is a specific length, worked out by taking into account no of cylinders, temp of exhaust, speed of sound, rpm etc. Looking at image I posted above the end of the resonator expands out to a larger diameter - my feeling is this may broaden out the frequency killing band.
It can get a little involved but not to bad if your high school maths is still up to speed.
I do not have the stuff in front of me right now but will post if I can locate it.
There was a chart that gave approximations for 4,6 & 8 cylinder motors and the lengths to use. From memory lengths of the dead end resonator tube, ranged about 21 to 38 inches for rev ranges in 1800 to 2400 range.
Quote below from jalopyjournal.com forum from a member called 'hotroddon'. This guy seems to have a handle on it.
"The 1/4 wave is generally just a J-Tube ~ a piece of tubing bent like a 'J' that welds into the exhaust and is capped at the end. A true Helmholtz is aimed at 1/2 wave cancellation and therefore requires more volume and a chamber (or multiple chambers) to cancel different waves and attenuate sound at different frequencies. The diameter of the pipe isn't very critical, although larger will broaden the RPM range effectiveness slightly. I have used as small as 1.5" and up to equal the main pipe with similar results. It is not about the volume of air moved in and out, but rather the cancelation of the wave. As for location, further forward will cancel more sound waves then further back, BUT if you don't get the length right, the rear most can sometimes catch a drone that the mismatched size doesn't. Honestly, the position isn't all that critical, but forward is better. 15-35 MPH is not the common area that Drone is dealt with, as we are usually just passing through that RPM band, not constantly driving it. Drone is best described as a dissonant sound that creates a thrumming sound - a fluctuating wave pattern. This is what a 1/4 wave resonator can solve. It is different than just a Loud sound at particular RPM. That is usually best cured with muffler design and or an H-Pipe smoothing the pulses. Because the 1/4 wave is a tuned length based on the speed of the exhaust, they work over a fairly narrow RPM band and fortunately drone usually occurs at a narrow band as well. You are talking about a fairly wide RPM range to kill with simple 1/4 wave. The math tells me that you need 38" for the 1200 RPM area and about 29.5 " for the 1700 rpm area. So a good compromise will be about 32-34" depending on which end of the RPM range is most annoying."
There is quite a good write up here in performancetrucks.net forums on how to calculate.
For another explaination and method of working out also here which seems to be a Porsche leaning forum
Last edited by Nev Williams; 09-24-2016 at 08:42 PM.
09-22-2016, 06:16 AM
Glass pack sidepipes
I represent that remark.............
