420r Drive by noise level.

[theslowman]

Hi,

I am a very new boy who is nearing completion of a 420r build.

I have just booked the novices trackday at Blyton Park this coming September but have just realised that "the day is subject to a 95 db(A) drive by noise limit"

As a complete beginner I have no idea if my lovely new car is going to get kicked off the circuit after its first lap.

Could somebody please give some guidance ?

Thanks

Patrick

[ScottR400D]

210bhp? Side or rear exhaust? 

95dbA sounds a bit tight to me. My R400 220bhp, side exhaust is usually over 100dbA  

 

[theslowman]

Oh dear.

Mine is a 210bhp, side exhaust.

How big a deal to fit a rear exhaust and where do I get the bits from ? I have had a trawl through the Caterham website and nothing leaps out....

As a complete new boy I am not exactly going to be going quickly - presumably this will help ?

[Handwheels]

Patrick - I'm taking my relatively new 420R to the novice session at Blyton too.  Iv'e got the standard side exhaust (minus the cat, which seems to have disappeared over the winter!).

When I put it through the IVA test last August it recorded 95dB - not sure how that compares with the drive-by testing at the track. However, I'm assuming I'll be able to be a bit more gentle if required to keep myself off the naughty step.

Look forward to seeing you there 

Richard

[theslowman]

Richard,

On Blyton Parks website they say that the noise meter is 20m from the track close to the start line on the exit of Twickers corner.

I assume that the IVA noise test is done at much closer range than 20m so if you can pass IVA then you should be able to pass the noise test at Blyton.

I suppose there is only one way to find out......

Mine is Hyper (Kowasaki) green. I'll see you there.

Bet I'm slowest !!

Patrick

[StevehS3]

If it helps I have seen 420s at Bedford where the drive by is 87dB at a distance of 20m. I obviously don't know whether they were driving in a way of being mindful of where the measurements are taken.

[theslowman]

Stevehs3

That is very much the correct answer !

Thanks.

P

[edo]

Funnily enough, when I was specifying my factory build 420, Caterham could not tell me what the rear exit track exhaust DB was, or the reduction!  I went with it to be on the safe side. 

I also notice on mine it just has one silencer box on the side, no separate cat - is that in the main box now?

[theslowman]

My kit was delivered in September 2021.

It has the side exit exhaust.

The cat is mounted immediately after the point where the four pipes come together.

The silencer is fitted almost immediately after the cat.

 

[edo]

Did they forget the CAT on my car?!!

[theslowman]

Presumably the cat is behind the silencer under the car ?

Or have you been a very naughty boy.....

[ScottR400D]

I think it's a bit optimistic assuming a car will pass because it passed the IVA. 
What are the parameters for the IVA test? At most tracks it's something like 3/4 of max revs at 1m distance. 
 

[theslowman]

According to their website its drive by and the device is 20m from the edge of the track at a defined location.

Presumably, easing off as you get close will help.

P

[Ralph45]

Caterham offer both side and rear exit exhausts with the cat in the main silencer so there's a fair chance it's one of those.

rear exit ref 3FX123A

side exit ref 370X0001A

   just looked and neither are in stock ! 

[Handwheels]

At my IVA it was tested at 5k roughly a couple of metres away. Think they said limit was 100dB

[edo]

that makes sense

[aerobod - near CYYC]

If it is too late to fit a rear-exit exhaust and the car does need to have a reduced noise output, a simpler solution that I use and quite a few other people I know use at noise restricted venues (on various cars) is a SuperTrapp system that can easily be added or removed from the exhaust.

There are clamp-on systems, but the lip on the side exit exhaust either requires a bit of tubing split in half to match the lip diameter as a clamping surface, the lip to be cut off, or a custom clamp. I machined myself a custom clamp.

In measurements that have been taken at venues for my R400D, 18 SuperTrapp discs reduce the sound level about 7dB, with only very slight drop in throttle response and a difficult to detect drop in power output.

[ChrisC]

It depends on so much, but as others have said a stock (or de-cat) 420R with the side exit exhaust will pass under a 100db static, assuming the exhaust is in good condition.  Drive by noise has a few additional factors, like sensor location, how hard your driving, gear used and weather etc.  On a quiet track like Bedford, I tend to start the day short shifting, and let the revs rise as the day goes on.  At Bedford your get a Noise board if you get close to the limit.  But I have not had a problem there yet with my 420R.  I believe the only circuit that does cause a 420R drive by noise problems is Brands.  This will change as the exhaust burns through its packing, and unfortunately the stock exhaust needs a fair bit of modification to make it repackable. 
 

I suspect your going there to learn your car, and therefore won't be ten tenths straight away, so go and enjoy and don't worry about noise.  

[Toughie]

#8, Edo.

"Caterham could not tell me what the rear exit track exhaust DB was"

I know there are far, far more knowledgeable members who will be along eight seconds after I post this, but until they do...

My understanding is that the dB level changes with the temperature and humidity of the day, plus, of course, the wind direction.  For this reason I've never been able to get Caterham or the people who service my car to tell me what noise level it emits.  They might be pushed into telling me what it is on a certain day at a certain time in a certain place, but wont tell me whether or not I'll pass scrutineering.

I have found that almost all circuits and organisers will do all they can to help you.  If you transgress the limits they'll often tell you where the meters are and suggest you back of the fortissimo pedal on that bit.

[Ralph45]

This is something that I have considered should I venture back on track as I believe my 420R would be to loud.

Sevens and classics offer a db killer that clamps on to the exhaust outlet in a similar way to the one James has fabricated.Its on the upgrade brochure download. It would be interesting hearing from anyone that has experience using one of these?

Just found the aforementioned and it's called a Decibel slayer costing 78 quid!

[aerobod - near CYYC]

With the Decibel Slayer you would need a "coffee can" exhaust tip to ensure the exit hole is at least the diameter of the exhaust pipe before the exhaust tip. With the SuperTrapp you change the exit cross section area by adding discs with 1mm gap between each disc. In my case I have about 120% of the exhaust cross section in exit area between the discs. The exhaust restriction in both types of device becomes the resistance to turning the exhaust gases through 90 degrees or more at exit.