how low??....small do you have to go?

stephen low · #1 (**permalink**) 10-21-2007, 03:22 AM

Have taken several noise measurements of the exhaust in advance of meeting the engineer.

Car generally has a two inch system with AU cats and 14 sports mufflers only, and is hitting around 93.5 dBA at rpms required. Tried first inserting steel restrictors at the flanges at the back of the cats with a 40mm hole and then again with a 28mm hole.

Second effort has gotten noise to 92.5 dBA.

What do I have to do to get under 90 dB?

Am thinking I return to exhaust shop for a pair of flanged hot dogs plus a pair of straight flanged pipes, the hot dogs for engineering and the straights for after.

Is there likely to be a cheaper way for me to meet the limit?

Cheers

BMK · #2 (**permalink**) 10-21-2007, 05:42 AM

stephen low

slowy,

Send Aussie Mike a PM. He has experimented a lot.

alffie · #3 (**permalink**) 10-22-2007, 02:00 AM

try a resonater at the rear. if all else fails use a factory set up to get rego

Jac Mac · #4 (**permalink**) 10-22-2007, 03:48 AM

On TVR ( SBF ) that is raced only- non roadgoing- we have been checked @ 87db with one large 'Flowmaster' type low profile ,dual 3" inlets- one 3.5" outlet into 'ovalised' 4" tailpipe 30" long. Test taken trackside at full throttle in third gear @ around 6500rpm.

Jac Mac

Aussie Mike · #5 (**permalink**) 10-22-2007, 04:52 AM

This test is at about 1 meter from the exhaust tip at 4K RPM.

Cheers

letsboogie351 · #6 (**permalink**) 10-24-2007, 03:51 AM

Slowy
how well do you know your exhaust man? I know of a couple of fellows who received a canary for noise. Their local exhaust man loaned them a couple of mufflers to pass the test. Then refitted the originals for them for a reasonable fee. I am told that this has been done a number of times. Alas the shop is not here in Melbourrne.
Food for thought?

Doug

stephen low · #7 (**permalink**) 10-24-2007, 04:29 AM

Doug

Did this for a road bike once, only a ZX6, and the smart exhausty said bring it back with the real exhaust pipe on it for me to check!??!!

The noise maker was in fast, just, legal.

But you did really need ear plugs. It was the best quasi horn I've ever had, a 10,000rpm twist of the wrist, and every driver looked in their rv mirror. Made it hard to miss me in traffic too for those dopy tin lidders out there.

However, am now planning to present on Friday and see what happens. Plan is to revisit exhaust shop, if needed, and get an additional pair of flanged mufflers into the car, to pass, but also have made up flanged straight sections to go in post engineering. At 93 dB I'm very happy with how is sounds and that ain't deafening for normal use.

Cheers

Rob. Smith · #8 (**permalink**) 10-26-2007, 05:22 AM

Slowy, I had some "fun" getting my 351 C passed. It started out as a stationary test on a "temporary" system to pass rego...just kept adding mufflers. In the end it passed the stationary test. Then I was required to pass a "drive by" test. It kept failing because it "whistled" too much. It was quiet to the point that standard cars were noiser. The muffler man was stumped but I tried a larger diameter pipe and the whistle dropped in decibels.
After creative mathematics the official report met and exceeded the required decibel level. I had a good argument point after the noise test man admitted that he used to pass harley choppers for rego. Ha ha ha..good luck

stephen low · #9 (**permalink**) 10-26-2007, 04:28 PM

I was a bit lucky at the test as I've measured mine at 93 at the right test revs 3950rpm but my man came out initially saying ok now you rev to 4500rpm,

I challenged his mathematics, ie 3/4 of max power rpm and he re-thought through and said your right rev to about 3,500 - 3600 and bingo - 89.3 dB.

Even he acknowledged these cars need a bit of burble.

So no exhaust work needed for the moment.

Cheers