Help - Noise Reduction

[martrogers]

I had a local company of "exhaust experts" install my system comprising of cat and muffler on each side and a tail resonator. I made it clear it needs to pass engineering at current sound levels.

Anyway, started the motor last weekend and whilst the sound was fantastic I fear it is too loud for engineering (and possibly the neighbours).

Does anyone have any tips for mods to quieten it down for engineering, I have limited space for additional mufflers but I could perhaps modify or replace the resonator which I suspect isn't doing too much for noise reduction.

Can restricting the exhaust damage the motor?

Any advice appreciated....

Mart

[Alvin]

have you try putting some steel wool in the exhaust. And tie copper wire around it and pull it out after the RWC. Or try and get a large washer and drill some holes in it and push it in. MAybe just a suggestion.

[martrogers]

Thanks Alvin, I'll try that.

[Rob. Smith]

G'day MARTROGERS,
Here's a yarn...I got a professional exhaust man to supply me with the appropriate mufflers. I had to tell him several times that it had to pass the stationary noise test that he actually had to do himself. He kept telling me that "these will make it sound good !" I finally got into his head that these mufflers were temporary...remember you built two 3 foot long hot-dog side pipes for me, they will be loud. So he sold me some really quiet mufflers....I built the temporary system and took it up for the stationary test and it failed. So he sold me two more mufflers and said...Don't drive it hard as the excessive back pressure will cause engine damage. The car at that time was untuned & on gas, so was a little hard to start. When the extra back pressure was added the thing wouldn't start. I had to attach a vacuum cleaner to the tail pipe to cold start it ....NO bull****... It passed the stationary test...just ! Then the RTA demanded a drive by test by another tester. At this stage the car was silent except for a loud whistle / gas noise. The drive by test in second gear at 2000 rpm was fine one way but too loud the other (exhaust exit was on one side ) I convinced the tester to take averages of the two results add them together and average them...I passed. Pay the man $200 and shake his hand. He told me later he worked for the RTA and used to pass custom harleys ! ?? Later I found that my 2" system should have been enlarged AFTER the mufflers to make a deeper sound which registers lower on the noise tester. My high pitched exhaust "whistle" freaked the machine out.
Smithy

[Philm]

Mr Smith

"I convinced the tester to take averages of the two results add them together and average them...I passed. "

Are you a lawyer as if I ever get divorced I will get you to represent me.

Phil

[Aussie Mike]

I've built a super quiet under body system for mine. No problems with starting and it seems to rev OK. I've got my own noise meter and it registers 87dB at about 4K RPM.

There's a bit of a theory I followed when I built it.

According to Boyle's Law The volume of a fixed mass of gas is inversely proportional to the pressure at a constant temperature PxV=K. That basically means that if you increas the temperature of a gas it's volume increases. If there's no room for it to expand then it's pressure increases.

So with that in mind the exhaust gasses are hottest when they leave the combustion chamber and cool as they make their way rheough the system before exiting at the exhaust tip. So with Boyle's law in mind the exhaust gasses are at their larges volume (size not noise) as they leave the motor. The larger the pipe we used the lower the gas pressure will be. We are trying to quieten the system down so it makes sense to try and slow the gas down.

To make mine run quiet I used 2.5" pipes out of the factory manifolds into the cat converters. I used 2 hi flo cats as these can be quite restrictive. I want to muffle not restrict the system. From the Cats I reduced the pipes size to 2" as the gasses are cooling and taking up less volume. These two 2" pipes run for about a meter before going into a Y and coming out as a single 2" pipe. This pipe then runs into a HQ Holden V8 oval section mufler and then on into another 2" round muffler.

Using small pipes and mufflers to quieten will increase the gas pressure and therefore the velocity giving that high pitched whistle.

I'll be in Sydney in a couple of weeks. I can throw my noise meter in my bag and bring it up and you can check your system.

Cheers

[Rare Iron]

Mike, are the Redback / Pro-Ex Mufflers still popular down-under? I've had dealings with their company before. We were contemplating launching a joint Aussie/US venture about 7 years ago.

[Aussie Mike]

Yep, still popular. The mufflers under my car are Redbacks. I've used a lot of their mufflers in the past and they seem to be pretty good quality at a good price.

Cheers

[Beejay]

I have Redbacks too, they appear very popular with the LS1 tuners.

Ben

[Rob. Smith]

PHILM...I laughed out loud at your reply... Thanks. I'm a dumb eleco that will try anything once; The noise tester had a sense of humour too.
People don't ask simple questions in the fear that they will appear stupid...Stupid people don't ask coherent questions !

[martrogers]

Aussie Mike

Thanks for your offer to measure my noise - when will you be in Sydney? - I'm in Forestville.

At the moment I have another problem. After 12 months of inactivity the motor started first time - whoopie. After half a dozen starts it is suddenly refused to start. The dash is powered but there is no response to turning the key. Fuses seem OK and the relay is clicking. Hope its not the starter solenoid - the starter motor has not been working hard as it has started quickly. I guess I should check power to the solenoid.

Needless to say, until I figure this out I cant avail myself of your generous offer.

Mart

[martrogers]

Rob

When did you do the test? - are the noise standards even tighter now? - Sounds like its going to be hard to pass...