Sport cat noise level

[Fen]

As some of you may remember my RS6 is going to be accompanying me to New Zealand in a few months (assuming we sell our house sometime soon...). For that reason I am being cautious with modifications as I don't want to do anything that will make registering it there a problem, however I do want to get the best from it and I'm pretty sure there is more model specific expertise in the UK than NZ where I believe my car will become one of something like 40 cars in the country.

One of the things I want to do is replace the cats. I understand that changing the exhaust is not an issue for NZ provided it doesn't become excessively noisy. When pressed I am told that might equate to 95dB measured at 45 degrees and 1m away from the exhaust tip and with the engine at 2/3 maximum revs, measured on a type 1 meter.

I have a noise meter of my own (if I can find it) so I can check the standard sound level, but I am concerned the RS6 already has quite a bellow and that sport cats would possibly tip it over the edge.

Can anyone give an idea of how much more volume is produced by changing the cats? Are 200 cell quieter than 100 cell and do 100 cell perform better (in terms of engine performance, not emissions performance)? Best of all does anyone have a Milltek or similar and a noise meter that can check for me?

I'm not too worried about changing the rest of the system as I think most gains come from the cats and I'm already supposedly running a part blocked pre-cat on the right bank - though if a full system is not noisier then I might go for one.

TIA as ususal.

[Wolverine]

My car registered 89 db at 4000 rpm according to the noise tester at a recent track day .... and my car has the full Miltek treatment with 100 cell cats. Anyone elsehere here who can confirm the reading was accurate ?

[grizz]

The system is not loud due to the car having turbos , i don't have any cats and even at 3/4 throttle it's not loud , put it under load it sounds like a NAS car..sweeet

[HyOctane]

is that 45 degrees C or F? Remember, the hotter it is outside, the louder the exhaust will be.

[grizz]

is that 45 degrees C or F? Remember, the hotter it is outside, the louder the exhaust will be.

It's a 45 degree angle to the tail pipe .

[Fen]

Ooh this looks encouraging... Thanks chaps.

95 is quite loud I guess, and there is a long way between 89 and 95. I'm a bit wary though as my 911 used to pull 116dB and even my 944 (with turbo) got black flagged at Silverstone on a 95dB evening for 106dB on the trackside meter.

[Fen]

Looking at pics of the Milltek cats they look to be the same section as the OE cats but I understood there are OE pre-cats also. Does the Milltek section replace both?

[Wolverine]

Miltek does away with the pre-cats.

Grizz is right though, turbos naturally supress the sound of the exhaust. The Miltek is definately not boy-racer loud, just deeper and more NASCAR. I doubt it would be more than 95 db ........

[allblack]

Fen

With my 100 cell & pre cat gut theres no not a huge amount of change - theres no way I'm over 95db - my wife didn't even notice I had had the exhaust done with the windows up...

You will be fine in NZ - the straight through exhaust on a Commodore V8 is much louder and get through LTSA regs. The boy racers in Jap cars are 120db+

Just take the factory cats with you and change them if you have any problems - if you changed them post LTSA they will never check again - there are no emissions / sound tests at MOT (WOF Warrant of Fitness) stage

S.

[grizz]

The milltek d/p's are a larger bore size , they don't have the precats that are at the top of the standard d/p & the milltek cats are in a larger case to allow better flow . i will get a noise level reading next week.