Exhaust loudness / compliance

[strikee]

Today my 85 targa failed the Australian ADR compliance test as the exhaust was too loud.

I need to understand how I can make it quieter.

For a start the catalytic converter has been cut out, so I also need to replace (also failed on this point).

The rear silencer looks old but I dont think it has perished inside, however I need to confirm this.

The heat exchangers look stock and in relatively good condition.

Im thinking I will search out a 2nd hand rear silencer and cat converter. If anyone has one let me know. Will post a WTB. I dont want to spend a bundle as once it passes I want to go SS.

Is there any where else in the system that would contribute to loudness?

Cheers
Ed

[DRACO A5OG]

or you can always try a baffle like this:



Speedway Motors, search cone

If you can find or borrow a oem cat and muffler, that should do it if headers are OEM

[strikee]

Is it just the cat and muffler that make it quiet? Silly question but I just want to check im not missing anything.

Cheers.

[DRACO A5OG]

Most of the dB's come from the Muffler/Silencer. I have a test pipe and it is just a bit louder/bassier then with CAT.

You could probably pass with just a Silencer

[Joe Bob]

The cat does help to quiet the exhaust. Matter of fact....I don't even have a muffler, just a cat on my 3.6.

[DRACO A5OG]

JB is of course just doing a test , I tested his car, it is nice and loud especially topless.

[strikee]

Do you think the cat will count for about 20db reduction? My car came in at about 104, needs to be mid 80's db.

[mb911]

no way are they gonna be worth 20 dbs I think your muffler is probably shot . you could put a premuffler on there as that will help muffle a bit as well

[moneymanager]

Deflectors to point the exhaust away from any sound booths will often do the trick in marginal cases.

[db_cooper]

At what RPM do they do the DB test? Probably not at idle. Maybe 1/2 redline on the tach? Do they use their own tach reading or the instrument in the car?

The 911 tach being electronic, some clever adjustment there can lower your DB noise too, if they use your tach and not their own.

[DRACO A5OG]

Damn, I forgot, the air box will contirbute to db's as well.

If OEM box, you will be okay as long as the cover has not been tampered with like mine being cut open or if you have a cone filter

[db_cooper]

Looked it up..pretty tough test: They did not have data for the 85 3.2..I found data for the 991 3.4 which was 94db @ 3750rpm.

4.2.3.3 Where the ESMP for that engine has not been determined by the testing
authority then the engine shall be brought to and stabilised at a speed as close
as the testing officer can achieve to one of the following speeds:
In the case of a passenger car or derivative, if the engine has:
(i) 5 cylinders or less 4000 rpm
(ii) 6 cylinders and is
manufactured before 1995 3200 rpm
manufactured in 1995 or later 3600 rpm

I would fiddle with the tach and see if a lower than actual RPM reading might solve the db issue.

Our engines are much quieter at 2200 rpm than 3200 rpm.

[strikee]

He asked for 4400 rpm. The car tachometer was used. Which is the "air box". Is this the one with the air filter? I know mine has a couple of broken clips. Cheers ed.

[db_cooper]

I think 4400 is off the chart..check your regulations or find another tester. Best I could tell it should been 3200PRM.

I think the tester pulled that one out of the air. A 3.2 is noisy at 4400rpm.

If some air box clips are missing..it wont matter. Some folks carve some big holes in the air box..that will make the DBs higher.