Exhaust Noise tests

[RSR]

Has anyone on here had their car tested? A 964 RS with cat bypass and cup bypass but standard final box was tested at 110db at 4500 rpm at half a meter at 45 degree from the exhaust exit. It failed to get on circuit.

Any other results with clarification as to distance tested and at what revs would be helpful. Current thinking is to replace the final silencer with another one in case the baffles have gone in this one.

Cheers Paul.

 

[Jamie Summers]

Paul,
My C2 with decat and cup pipe tested at 107db at 4500rpm 45degree angle etc. Funnily enough it is fine on 98db drive by tests so have made it on to every track I have tried despite red stickers !!!

 

[RSR]

Thats interesting and not far off. The circuit in question was castle combe on a noisy day!

One other area that can make a difference is depressing the clutch to avoid spinning up the lay shaft gearing that then just rattles around adding to the noise. Is this something you do?

 

[Matt]

I always have my foot on the clutch pedal (and try to hide the rev counter as well..)
I 've tested at just under 105 with smaller cat (I think its non standard), std back box & a G-pipe thing instead of the final silencer.
It fails bedford every time but I short shift on track by the microphones which appears to work in the past.
Seems to be OK on noisy (105dbA) days - Donington, Brands, Snetterton, Oulton
Matt

 

[Melv]

Paul -do you want a prize? []

Same set up on my Cup Car gave 107db.

I added a C2 silencer across the back and this has reduced to about 100-102db.

However, loosed baffle in the final silecncer has put the noise up a bit.

Make sure engine is really hot and depress the clutch.

However, most noise tests a nonsense when you consider they are done on tarmac and often near buildings (Castle Combe in particular). Also grossly unfair on rear engined cars!!

Also, there are discrepancies bewteen the poise measureing requirements. Combe -0.5m at 75% max revs at 45 degrees; Goodwood 0.75m at 75% max revs at 45 degrees; Bedford 4500rpmish at half a metre ish at whatever angle the tester waves the machine in the vicinity of the exhaust pipe......

I have a silencer from Merlin at Combe that replaces the tailpipe on the Cup Car and reduces a decible or two if I am borderline....you are welcome to try it!

 

[SimonExtreme]

I had always suspected my car was noisy (dcat and cup pipe) but I guess these figures confirm it []

I have been too busy to do any trackdays so far this year[] and wonder whether I would get through noise testing anyway. I looked into this at the beginning of the year and concluded that to get through noise testing without a reduction in power due to restrictive exhausts, you need something custom. When considering all of this, it would seem to me that the standard rear box is poor for both nioise control and flow while the G pipe isn't a good solution because it still follows a tortuous route. I would go with a box across the back but I would get it made by a specialist as I think the C2 standard box isn't much cop!

 

[Melv]

"I think the C2 standard box isn't much cop!"

And why not Simon? You've tested it 'exhaustively', no doubt...[]

I got a s/h one for thirty quid and it chopped a whopping 5 or so db off and with no discernable difference in power above 4200rpm................fact! Ask the guys who try to keep up in GT3 RS's.....[]

 

[SimonExtreme]

ORIGINAL: Melv

"I think the C2 standard box isn't much cop!"

And why not Simon? You've tested it 'exhaustively', no doubt...[]

I got a s/h one for thirty quid and it chopped a whopping 5 or so db off and with no discernable difference in power above 4200rpm................fact! Ask the guys who try to keep up in GT3 RS's.....[]

But Mel, how much faster would you be with a decent rear box. I haven't tested them myself but Hayward and Scott have. I believe they have also taken one apart and their own design gives the same overall noise but is freer flowing.

There is an interesting question as to whether you need any freer flowing with the state of tune you have. It could well be that the exhaust isn't limiting your maximum power and therefore it doesn't matter. From what I have been told by various specialists, after a certain point the fueling becomes an issue and after that has been sorted, the ports and cams limit how far you can go. Getting to the bottom of some of these questions is the point of another thread I have started[]

 

[937carrera]

Section E12.17.8 of the MSA blue book gives the test details. There are two basic methods

a, 0.5m from each tailpipe, at an angle of 45 degrees from the exhust, limit 105dBa
b, at either side of the car, 2 metres from the centre point of the car (1m from bodywork) at a height of 1.2 m from the ground, limit 93dBa,.... or 8m from the side (7m from bodywork), linit 81dBa

There are to be no reflective surfaces within 3 metres for test a and 10m for test b.

edited to add detail for test b and full MSA reference

 

[Melv]

Thanx for this -can I quote it??? []

And what do the MSA suggest for % revs etc?

Simon -my car is plenty fast enough for track days for me [8D] -be different if I was racing, and I'm not -some track dayers seem to forget this....[]

 

[937carrera]

Melv,

Of course you can quote it, but as you know many people do not like being told how to do their own job ![:-]

MSA specifies 75% of maximum RPM, best get hold of a blue book for the definitive details - there are different levels for different distances, though I don't know to what extent circuit agreements with councils actually accomodate the variations.

 

[SimonExtreme]

ORIGINAL: Melv
Simon -my car is plenty fast enough for track days for me [8D] -be different if I was racing, and I'm not -some track dayers seem to forget this....[]

Fair comment, Mel. I happen to get a lot of pleasure from the technical and engineering side of things and I like to think about how to get the best out of the car both driving and engineering wise. It isn't about the speed. I just hate bad or comprimised engineering.

After all, you can have a lot of trackday fun in far cheaper and maybe quicker cars than a 964 RS (even your cuppie!). In fact, a mate has a Peugeot for trackdays and probably gets more "bang for his buck" than any other trackdayer I know.

 

[RSR]

Thanks for all the feedback. I'll have the final silencer checked and if there's no sign of baffle damage then the car will need the cup or cat bypass replaced to get through the noise test at the strict circuits.

 

[hunter]

Paul remember I used to get 114db in the old days when things were not an issue,good to see you again

 

[Laurence Gibbs]

In a thread on another forum some time ago now, someone "in the know" suggested going the twin outlet route to reduce noise. The theory being the two outlets would split the noise in two, making the static test results lower. The theory makes sense(I think) but I have no idea if it's true in practice. The 993 type exhaust does this but also uses twin cats and boxes so I guess that would be unfair to compair but Lee's cargraphic system would be interesting to test.

 

[carreraboy]

Have you heard Shaun's the ex=des sturdee car on full hammer! The twin does dilute on low revs but on full resonance with a straight thru system and no silencers sound the DOGS DANGLY BITS MITTEN DER FLAMIN THROWEN MEIN COMRADEN MIT DER YELLOW PERILEN....

 

[Tankman]

Excuse my ignorance gentlemen but, do I have to pays my money for a trackday before I get the thing noise tested? Bit expensive if it fails eh!

 

[Laurence Gibbs]

Some track day companies will lend you a niose test meter for a small fee, can't remember which specific ones. Other than that yes some organisers will not refund you if your car fails! Moral is get it tested first! Most post up what limit is required. You are then expected to bring a car that runs under that limit and they view it as your fault if you don't!!
As an aside some nokia phones I believe have a noise meter on them, I have no idea how accurate they are though.