Too loud for track day!

[Adrian5]

Hi all

I've just come back from the track day at castle combe. Bought my 991S a couple of months ago and had a few hours free so thought i would try and get a taster session. Turns out it failed the noise test at 110Db (105 limit). Test performed at 6000 revs. Irrespective of whether sport, sport plus or neither are selected there is a distinct change in noise level around 4000-5000 revs so seems the exhaust set up is the same once the engine hits this point. Guys there said they're sure other 991S cars have been on the track at castle combe so any ideas? Only thing i can think of is that i DO NOT have a sports exhaust. I beleive the sports exhaust works by bleeding sound back in to a chamber by the cabin so could it be that the sports exhaust cars emit less noise from the pipes by absorbing it in the cabin?

Just glad i hadn't paid for a day. Any ideas greatly appreciated!

 

[tscaptain]

Why was the test done at 6000rpm? I thought it was either 105 dB max at 3/4 max rpm for a "noisy" day or 4500rpm/ max 100dB for a "quiet" one

 

[ralphmusic]

Today at CC I was 101, last year 97. "That was then sir" was the comment. It all seems hugely variable to me.

 

[Adrian5]

Good question. first tme i've had a car tested so i just presumed that as the first main red line is at 8000 they used that to work out the 6000rpm (even though the redline starts at 7500. You think this is the problem, was it supposed to be tested at 5600?

 

[tscaptain]

When does the rev limiter cut in? Not 8000 rpm, I know. Of course with rear engined cars there is the additional problem of mechanical noise from the engine - an unfair disadvantage compared to front engined cars when noise testing.

 

[Adrian5]

Mmmm. Not sure without heading out for a spin but it's definitely around 8000, probably a little under say 7800. I'll check tomorrow and let you know unless anyone has the answer []

 

[ralphmusic]

991 brochure has 7,400 for maximum power for S model

 

[Adrian5]

Have ordered a sound meter so will do some tests over the weekend. Would be really interested in hearing from anyone who has taken their 9912S on a track day and if so what exhaust they have fitted. Also anyone know if there is a way of disabling the exhaust valves they seem to open up at 5000 revs irrespective of the mode selected. Failing all that i'm going to have to look at some kind of silencer. Bizarrely i think it's also likely that the car would pass the quiet track day test due to the lower revs)

Any bright ideas for testing greatly appreciated []

 

[ralphmusic]

I really suggest you call Steve Kevlin at PCGB +44 1608 652911 - He runs the track days and knows the variations of each track in testing. I have been at Goodwood where 991S have run with no noise problems and Goodwood is pretty strict on noise testing.

At Castle Combe yesterday they insisted I ran at "near 6,000" because the guy in a GTS before me had offered that as 75%, it should be 5,400 rpm for 75% - it is so random at times. There was a 997 GT3 there as well and that got through.

 

[Adrian5]

Thanks for the advice. I had a long chat with Steve about it yesterday. Did a few tests there and then and he couldn't believe it had failed with similar results to the Lambo that also turned up and failed the test. Ultimately not allot Steve can do as the test is run by the track.

Part of the 991 selling point is the improvements made to engine noise. As mine is standard (albeit with Sport+) and appears to be the first to have failed the test my suspicion is the meter yesterday was either out of calibration (i see your own test increased significantly), there is a way of disabling the valves in the exhaust for the test or it's because mine has the standard exhaust with less noise fed back in to the cabin instead of out the back of the car. All speculation at this point though.

Plan to do some tests over the weekend and will see if OPC swindon will let me repeat them on their Demo 2S with the sports exhaust. Would be interesting to hear the results of tests of anyone else on the forum who has taken a 9912S on a track day. Heads up though for anyone looking at a new GT3 or Turbo!

Adrian

 

[Lancerlot]

I think the Turbo should be fine.

Not much help to you, but we used to stuff wire wool up the exhaust to pass the noise test when we were rallying. [8|]

One good blast at 7K on the track would blow the whole lot out and "Bob's your uncle" full power restored once again! []

I also remember when the Porsche factory team was rallying many years ago, seeing the cars in scrutineering with large bungs in the their systems that were promptly removed by the service crew when back outside the scrutineering bay, leaving a completely open exhaust with no impeding silencer system whatsoever - a glorious sound. [8D] Happy Days. []

Regards,

Clive.

 

[Geoff_Fields]

You can prevent the exhaust from going to loud mode by temporarily blocking the open air side of the vacuum actuator.

 

[Motorhead]

Adrian,

If you're purchasing a sound level meter, you really need a calibrator too which produces a 94dB 1kHz reference signal. Hopefully, the Castle Combe stewards performed a calibration on their equipment prior to measuring your car. Did they have the A-Weighting filter activated?

The Motorsport Vision Trackdays site gives the approved procedure for sound pressure measurement at their circuits:

The initial test is a static test which is carried out using a handheld meter. Each car is measured 0.5 meters away from the exhaust at a 45 degree angle when the engine is being held at ¾ of the maximum RPM. In cases where the vehicle has two separated exhausts the measurement will be taken ...... from the median point between the two.

Personally, I think that a drive-by test would be a more appropriate measurement method and note that this is in place at a number of MSVT circuits - Bedford Autodrome, Brands Hatch, Oulton Park and Snetterton.

Jeff

 

[Geoff_Fields]

Here is the valve actuator switch. Just cap off the the open nozzle to prevent exhaust going to loud mode.

This is a 997 GT3 so other models may have slightly different location.

 

[Adrian5]

Thanks everyone. Geoff any chance of a slightly zoomed out photo so i can identify the location on the car a little easier (or just tell me where to look?)

 

[jonathanw]

Adrian

I can say for sure that the noise from the sports exhaust is much much louder that when not engaged on the 991CS. Speak to the guys following me on the recent SW tour and they will vouch for that and that is for the entire rev range. It is not to say that the standard set up is quite though.

In the 997 you could inactivate the sports exhaust or keep it on altogether. In the 991 you can only view the engine from underneath unless you take the back bumper assembly off!!

 

[Geoff_Fields]

Adrian
Mine is a 997 GT3, so zooming out will not help you. On 997's the valve is located top right of the engine. The 991 access is unknown to me and having had a quick look at one, seems it may be a lot more difficult to get at!

 

[Adrian5]

Thanks Jonathan. From what i understand the sports exhaust essentialy adds a chamber near the rear of the cabin. Once engaged further valves in the exhaust are openend to bleed sound in to that chamber for a richer sound in the cabin. As far as i'm aware the rest of the valves are the same as power output etc is unchanged. My non sports exhaust also opens right up past 5000 revs with a real marked difference (hence the reason it's failing the test). Have you had yours measured at a track day?

 

[Adrian5]

I would love a spots exhaust by the way. Ability to pass the noise test to take on the track would be a very good excuse!

 

[Adrian5]

ORIGINAL: Geoff997

Adrian
Mine is a 997 GT3, so zooming out will not help you. On 997's the valve is located top right of the engine. The 991 access is unknown to me and having had a quick look at one, seems it may be a lot more difficult to get at!

Ok, thanks Geoff. Interesting none the less. If i can't find another solution i'll have a go and setting up a way of blocking the bleed from the valve. Will just need to be something i can access without having to remove the bumper each time!