Discussion
I have a 964 RS CS which has had few modifications - larger throttle body, air filter, modified ECU, cup exhaust - running approx 300bhp. Had it noise tested at Castle Combe - 103db at 4k rpm (and yes I did dip the clutch). Needless to say they wouldn't let me on the circuit :-(
Really want to do Bedford and Castle Combe, so what can I do to get below the 100db without losing too much power?
A friend of mine has a Supertrap that he is selling, wants £150 (said it cost him £250?) - any good?
I intend taking the car to Colin next year to get a few more modifications done to up the power, maybe it is best to wait until then and have the exhaust set-up properly? In the meantime use the Supertrap?
Any advice greatly appreciated.
Mark
Really want to do Bedford and Castle Combe, so what can I do to get below the 100db without losing too much power?
A friend of mine has a Supertrap that he is selling, wants £150 (said it cost him £250?) - any good?
I intend taking the car to Colin next year to get a few more modifications done to up the power, maybe it is best to wait until then and have the exhaust set-up properly? In the meantime use the Supertrap?
Any advice greatly appreciated.
Mark
With regards Bedford, my 964RS is around the 101-102db mark and I got into Bedford. The circuit owners do the testing and they understand that 911's are particularly sensitive to the .5 metre noise test at 4K revs and as a result are prepared to bend the rules alittle.
I've tried a decibel insert (reduced noise by about 1db) but you need to attach it inside the exhaust tip (means drilling a hole in the exhaust!)
I've heard these supertrap things can cause performance issues as they mess up the back pressure from the exhaust (9M may correct me on this!!!) You also need to weld them to the exhaust. Heard stories of bolt on ones doing impressions of exocet missiles.
I think (9M may correct me again) but the best way to reduce the noise is to put the rear silencer back on.
>> Edited by paulc on Wednesday 4th December 11:20
Hmmm, I have this quandary, too.
With the current system, my 964RS sounds like a Le Mans refugee, absoultely magnificent noise. Not just loud, but a pure flat six howl. Just ask rthierry or AJ Lintern
However, I kept the rear silencer as it sounds like a tart's MX-5 with it on, and if/when I track the pants off it next year, I may have to chuck this offending item back on.
With the current system, my 964RS sounds like a Le Mans refugee, absoultely magnificent noise. Not just loud, but a pure flat six howl. Just ask rthierry or AJ Lintern
However, I kept the rear silencer as it sounds like a tart's MX-5 with it on, and if/when I track the pants off it next year, I may have to chuck this offending item back on.
Bedford Ive never been to, but you are not missing too much by not going to Coombe. Its a nice enough track but there are noisy days ie 105db available at much nicer tracks like Brands or Donnington . Even Goodwood had several 105db days per year.
I think Cadwell park (awesome place although bit scary for 911s in the gooseneck) has either unlimited noise or at least 105db.
I think Cadwell park (awesome place although bit scary for 911s in the gooseneck) has either unlimited noise or at least 105db.
Probably try my luck at Bedford based on what you’ve said. I really want to do this circuit, as it is big, wide, with very little to hit. Means I can push the car and myself harder without fear of damage!
I have been to Combe several times in a previous car, and I really like it, mainly as it is a fast circuit – each to their own.
Domster, I fear you are very much in the same boat as me, and you will have to do something to get onto certain tracks - I have heard they are getting stricter as time goes on. Also what do you mean “if” you track the pants off the car, why have you not done this already, and why is it in question?
I read somewhere that if you were to noise test the 911 on a soft surface, such as grass, then it would stand a chance of passing most noise restrictions as the engine noise would not reverberate so much...?! Basically we are penalised because the engine is in the rear
No further forward really
I have been to Combe several times in a previous car, and I really like it, mainly as it is a fast circuit – each to their own.
Domster, I fear you are very much in the same boat as me, and you will have to do something to get onto certain tracks - I have heard they are getting stricter as time goes on. Also what do you mean “if” you track the pants off the car, why have you not done this already, and why is it in question?
I read somewhere that if you were to noise test the 911 on a soft surface, such as grass, then it would stand a chance of passing most noise restrictions as the engine noise would not reverberate so much...?! Basically we are penalised because the engine is in the rear
No further forward really
Bedford is a wonderful trackday venue, very open and very fast I have been there with the PCGB. However this weekend I went with some friends to a day organised by the Subaru Impreza Drivers Club.
The static noise test was only 85db - yes 85
Needless to say many cars were refused entry.
Furthermore there are three drive by measuring points also and once the day started a few more cars were black flagged (purely for noise) and sent home after complaints from the nearby village.
Eventually the circuit was reduced in length by a mile (nearest the village) after Jonathon Palmer himself arrived in his helicopter and took sound levels in the village.
Track was jolly empty after that
Paul
The static noise test was only 85db - yes 85
Needless to say many cars were refused entry.
Furthermore there are three drive by measuring points also and once the day started a few more cars were black flagged (purely for noise) and sent home after complaints from the nearby village.
Eventually the circuit was reduced in length by a mile (nearest the village) after Jonathon Palmer himself arrived in his helicopter and took sound levels in the village.
Track was jolly empty after that
Paul
!!!!! I followed that M5 for a number of laps as a passenger in an Audi S4 biturbo 4WD. The M5 had incredible traction out of the corners (bearing in mind it was a wet day) and a lot of the Scooby owners were surprised. With so few cars on track it was an excellent day
I believe that Bedford do not do many weekend trackdays and so lowered the limit to appease neighbours that are usually working during midweek days.
In my opinion, noise is going to become more of an issue as more and more of us join the ever growing trend of track driving.
Manufacturers of exhaust systems will have to be on their toes to produce powerful pipes that are not too loud or we jeopardise the future of our minority 'hobby'
Paul
I believe that Bedford do not do many weekend trackdays and so lowered the limit to appease neighbours that are usually working during midweek days.
In my opinion, noise is going to become more of an issue as more and more of us join the ever growing trend of track driving.
Manufacturers of exhaust systems will have to be on their toes to produce powerful pipes that are not too loud or we jeopardise the future of our minority 'hobby'
Paul
Hmmm, tricky one. We tested an RS with Motec not too long ago, first mit cat then without (straight through pipe) and the difference in power on the rollers was negligible once the mapping was trimmed. So I am not sure that the silencing is that important once a certain backpressure is reached.
My preference for the RS is no cat and cup pipe, and this will run at 103-106 depending on the engine/cam/meter/environment. As a result I have been contemplating a silencer tailpipe and have invested in my own noise meter so I can have a serious play. If there is enough interest I'll make a few different tailpipes and test their effect on the rollers and for noise so we can offer a proven solution.
One obvious observation however that we applied to our 930 race car, is that the engine noise also contributes to the noise level, so if you extend the tailpipe away from the rear of the car by a good few inches you will reduce the measured level at 0.5m. Secondly any trumpet effects of the pipe make matters worse so keep it constant diameter (I suggest you try 2.5") from the silencer to the outlet. Finally, if you then put an elbow on the end of the pipe so that it can be pointed down or simply away from any drive by test position, you will definitely pass the test.
So, go out, chop a coupling from any 964 exhaust section, weld a 12" straight pipe and a 90 degree elbow on to it, and try again, I bet it would kill at least 3-4 dBa.
>> Edited by NineMeister on Wednesday 4th December 22:33
My preference for the RS is no cat and cup pipe, and this will run at 103-106 depending on the engine/cam/meter/environment. As a result I have been contemplating a silencer tailpipe and have invested in my own noise meter so I can have a serious play. If there is enough interest I'll make a few different tailpipes and test their effect on the rollers and for noise so we can offer a proven solution.
One obvious observation however that we applied to our 930 race car, is that the engine noise also contributes to the noise level, so if you extend the tailpipe away from the rear of the car by a good few inches you will reduce the measured level at 0.5m. Secondly any trumpet effects of the pipe make matters worse so keep it constant diameter (I suggest you try 2.5") from the silencer to the outlet. Finally, if you then put an elbow on the end of the pipe so that it can be pointed down or simply away from any drive by test position, you will definitely pass the test.
So, go out, chop a coupling from any 964 exhaust section, weld a 12" straight pipe and a 90 degree elbow on to it, and try again, I bet it would kill at least 3-4 dBa.
>> Edited by NineMeister on Wednesday 4th December 22:33
Hmmm,
Now if you could run that pipe back so it exits just behind the door (ala cobra's etc) you would have a longer pipe, further away from the engine and not protruding a foot out back! Just a thought.
There is probably a good reason for not doing this? And before anyone mentions it. Yes I know that an awful lot would get in the way (trailing arms, driveshafts, wheel arches etc).
>> Edited by lemon yella rs on Thursday 5th December 14:43
Now if you could run that pipe back so it exits just behind the door (ala cobra's etc) you would have a longer pipe, further away from the engine and not protruding a foot out back! Just a thought.There is probably a good reason for not doing this? And before anyone mentions it. Yes I know that an awful lot would get in the way (trailing arms, driveshafts, wheel arches etc). >> Edited by lemon yella rs on Thursday 5th December 14:43
lemon yella rs said: Hmmm,
>> Edited by lemon yella rs on Thursday 5th December 14:43
I thought of this idea a while back, yeah sort of like a cobra or Caterham side pipe but in reverse but with a u shape bend at the end so the gasses exit to the rear of the car just to plonk on for track days. As it is not so much the exhaust noise that clobbers a 911, its the noise of the engine engine buzzing away 0.5m away from the measuring device. However even the new 996 with a standard exhaust would fail that strict Bedford 85db test (I think superlightr's new 996 was even over the 98db at Goodwood but it was a 105db day so he was ok)
Because of the flooorpan design of the 964 you could not bring the outlet further forward than the rear wheelarch.
Food for thought. If it is static testing only, simple: go for a twin outlet system. The noise will be measured at one side only, and if you play your cards right the overall level will be 103-104, but a single side measured could be as low as 98-100. Take a look at the 993RS, mine with a GT exhaust and 100 cell cats runs at 98-100.
We already make a composite LHS bumper section with the exhaust cutout (like the 965), so the rest is down to pipework only, a restrictor in the rhs and a cross pipe to the left may just do enough.
Food for thought. If it is static testing only, simple: go for a twin outlet system. The noise will be measured at one side only, and if you play your cards right the overall level will be 103-104, but a single side measured could be as low as 98-100. Take a look at the 993RS, mine with a GT exhaust and 100 cell cats runs at 98-100.
We already make a composite LHS bumper section with the exhaust cutout (like the 965), so the rest is down to pipework only, a restrictor in the rhs and a cross pipe to the left may just do enough.
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