track day noise compliance - options?

[cornershop]

folks,

managed to fail the noise test on my first trackday at Brands last week by some way - 106dB versus the evening limit of 102dB.

was thinking of one of these supertrapp things - http://www.demon-tweeks.co.uk/products/ProductDeta...

are there any other options? i have a 3.5" tailpipe (not rolled)

cheers
sp

[David W]

In my experience of cars failing the noise test at our events, these devices appear to reduce the noise by between 0(yes zero) and 3dB (max) depending on what condition your existing exhaust sytem is in. As a long term fix I'd be inclined to sort the exhaust system rather than use a super trap. Exhaust can often be much impeoved by a simple re-pack.

BHP

[speedychrissie]

As david has said you may be disappointed by how much quieter the additions make the exhaust.

One of these may be an alternative:
http://www.merlinmotorsport.co.uk/p1576/MERLIN-MUF...

We have a couple of them for the racing cars nad they have reduced the dB level, but I have never got around to quantifying by how much.

Personally I would suggest that at 106dB you would be safer getting a much larger silencer fitted by someone who knows exhausts.

[muckymotor]

I've been in the same position as you and I'd agree with replacing or repacking your exhaust.

It makes for a much less stressful time when waiting for the noise test

[cornershop]

Thanks fellas

I'm loathe to change the exhaust as a) there's nothing else like it soundwise for my 1987 911 and b)
its in perfect condition and costs circa 1200 Euros brand new!

That Merlin one won't fit as the max OD available is 3" - will see if a custom can be made.

Thanks again
SP

[boyzee]

I to failed the noise test at castle combe last friday with my skyline gtr.I have a 4inch exhaust fitted and merlin sold me a bung that fits my exhaust.I had to have some metal strips wealded to the part they sold me but i can just bolt it on when need be.Before the bung was fitted my car registered 106db at brands it only records 102db but combe makes you rev to 4500rpm.With the merlin bung it was 96.8,it cost £62 inc vat.It only takes 2 minutes to fit or remove.

[cornershop]

boyzee said:

I to failed the noise test at castle combe last friday with my skyline gtr.I have a 4inch exhaust fitted and merlin sold me a bung that fits my exhaust.I had to have some metal strips wealded to the part they sold me but i can just bolt it on when need be.Before the bung was fitted my car registered 106db at brands it only records 102db but combe makes you rev to 4500rpm.With the merlin bung it was 96.8,it cost £62 inc vat.It only takes 2 minutes to fit or remove.

thats interesting, thanks for your input. was there much difference in performance?

a pic would be great if you get a moment

cheers

[boyzee]

To be honest we had not taken the gtr to combe before so without timing it we don,t really know if it made the car slower,having said that i think the difference on our car was very minamal.The people at merlin were very helpfull as they let us try the exhaust and get it tested before we had to pay for it.Our car makes 680 BHP so as i said without timing with and without its hard to judge.If you click onto the merlinmotorsport site you can see the picture of the merlin muffler it fits inside my 4" exhaust the outside dieameter is around 1/4" smaller than my tail pipe but im sure they can give you a correct size.Do you run twin or single pipes?Hope this is of help to you.

Edited by boyzee on Sunday 14th June 15:10

[Mickyturbo]

Was at Croft last weekend,where the noise limit is 95DB,which is very low in my mind.Anyway,I failed,got a 99 DB reading.So with the aid of a large dogfood tin,wire wool,wadding,jubliee clip and a drill,we made up a bung of sorts.Got the noise down to 94DB,and didnt make the car feel any slower.Here's a picture

Not pretty,but it worked for the 2 days on track!!Regards,Micky

[Matt_N]

Combe's noise tester's are notoriously optimistic ime.

A couple of friends race cars always seem to read at least 3 or 4 db's higher at Combe than anywhere else.

[cornershop]

boyzee said:

To be honest we had not taken the gtr to combe before so without timing it we don,t really know if it made the car slower,having said that i think the difference on our car was very minamal.The people at merlin were very helpfull as they let us try the exhaust and get it tested before we had to pay for it.Our car makes 680 BHP so as i said without timing with and without its hard to judge.If you click onto the merlinmotorsport site you can see the picture of the merlin muffler it fits inside my 4" exhaust the outside dieameter is around 1/4" smaller than my tail pipe but im sure they can give you a correct size.Do you run twin or single pipes?Hope this is of help to you.

Edited by boyzee on Sunday 14th June 15:10

thanks again - mine is a single 3.5in

[cornershop]

Mickyturbo said:

Was at Croft last weekend,where the noise limit is 95DB,which is very low in my mind.Anyway,I failed,got a 99 DB reading.So with the aid of a large dogfood tin,wire wool,wadding,jubliee clip and a drill,we made up a bung of sorts.Got the noise down to 94DB,and didnt make the car feel any slower.Here's a picture

Not pretty,but it worked for the 2 days on track!!Regards,Micky

Genius!

[Chris71]

Am I right in thinking you're in a Porsche? If so there is a known 'trick' for rear engined cars, might be worth enquiring in the Porsche section? I think the idea is that you get a lot more mechanical noise due to the proximity of the engine so you need to test it warm.

Failing that (and indeed lying to or pleading with the marshalls ) the bolt-on external silencers seem to work well. I haven't seen the type linked above (although that's not to say they aren't good) but the TVR boys use additional cans to great effect.

[cornershop]

Chris71 said:

Am I right in thinking you're in a Porsche? If so there is a known 'trick' for rear engined cars, might be worth enquiring in the Porsche section? I think the idea is that you get a lot more mechanical noise due to the proximity of the engine so you need to test it warm.

Failing that (and indeed lying to or pleading with the marshalls ) the bolt-on external silencers seem to work well. I haven't seen the type linked above (although that's not to say they aren't good) but the TVR boys use additional cans to great effect.

yes indeed Chris, 87 911 - car was very warm having idled for 5 mins, clutch was dipped. have a drilled airbox lid, guessing this won't help either?

not a bad shout re TVR bits - saw this after a quick google

http://www.actproducts.co.uk/shop/silencing-trackd...

Edited by cornershop on Tuesday 16th June 20:36

[antnicuk]

Javeline have one of those ACT silencers which they kindly leant me, it only had an 1 1/4 outlet (my exhaust is 3 inch) and although it quietened things down a lot, it capped my boost from 0.7 to 0.3 bar boost which isnt good for a turbo engine, it also puts more strain on the turbo and increases EGT's, you should be ok on N/A 911.

I have had to have a huge repackable silencer made, dont know the results yet but should do next week.


If you are going to be doing trackdays regularly you may consider selling your system and buying a track day friendly one. I hate that wait while they sound test you!

Edited by antnicuk on Tuesday 16th June 21:25

[mat205125]

Matt_N said:

Combe's noise tester's are notoriously optimistic ime.

A couple of friends race cars always seem to read at least 3 or 4 db's higher at Combe than anywhere else.

It is essential that noise tests are done correctly. Trackdays are not race days, and not governed by the MSA, however the "normal" 1m, 45 degrees, and 75% rpm is a good static test.

It's important that if the test takes place in the assembly queue, that a "good" gap is kept between the car being tested and the car behind.

I find the 106db reading in the OP's post difficult to believe from the 911 in his profile unless he has a silly exhaust on it.

Drive-by noise should also be considered. A quiet exhaust is great, but 50mm open throttle bodies might annoy the machine. Likewise a turbo car "chugging" out 100db with no load will be making all kinds of weird and wonderful noises when the 2 bar boost is whistling through the engine ...... Drive-by noise transgretions associated with DCOE carbs is a medal of honour in my opinion

[cornershop]

[quote]

I find the 106db reading in the OP's post difficult to believe from the 911 in his profile unless he has a silly exhaust on it.

Drive-by noise should also be considered
[/quote]




http://www.youtube.com/watch?v=Qr4u9oQdL7c

[Herman Toothrot]

Is cutting the back box open re-stuffing it and sealing it back up an option. I'm going to do that to mine before the next trackday as although I was passing static tests at 98dB I did get re-tested as drive by my car was on the loud side.

[silverthorn2151]

We failed several tests in our Radical SR3 and I have lost count of the number of times we took the end cap off, repacked, packed around the silencer etc etc etc. Even bought a 102db exhaust from Radical wich was rubbish.

Eventlually had an exhaust made and we tested at Snett recently at 98db on a 105day!

On the other hand, we ran at Le mans Bugatti recently wuith the straight through fitted as they didn't test and didn't seem to care.

My advice would be to bite the bullet and get yourself an exhaust that you can be sure will pass tests. You waste a lot of time, effort and money doing otherwise. You want the car to run as it should as well, and the wrong exhaust can stiffle the engine.

Picking up a couple of points from the thread, most tests are in isolation, not in a queue in my experience.

I would also reiterate the point about warming up first. The example I witnessed was a Countach at Goodwood that failed when cold, the guy warmed it up, then retested it and it passed!

I'd also suggest that sitting at a test at 75% red line revs with a cold engine isn't the best thing you could do!

Chris