Noise limits - a real PITA

The Oily Bits S2 Specific Topics
1

Last weekend Lotus Club Sweden arranged a track day at Ring Knutstorp.
Noise limit is 95dbA (full throttle drive-by) on all Swedish tracks.

On this day there were 5 supercharged cars (3 exiges and 2 elises) and all of us got black flagged.
I managed to “win” with 105db - and did it with a newly repacked 8x24 backbox.

We got lots of help trying to get within the limits and to identify the noise generators.
Lowering the revs to 6000-6500 got us all under the radar and the supercharger was identified as the source.
We were told that “You guys could put all the mufflers in the world on these cars but you still would not pass”.

So what can be done? How do you silence a supercharger?

Ideas are most welcome.

/Michael

2

This is exactly the reason I opted for my NA Exige with the Komotec SC conversion as the supercharger used is near silent. Don’t get me wrong, love the sound of an SC, but its just something else adding to the DB’s and can mean you’ll either have the problem you’re having or have to have a ridiculously restrictive/quite exhaust to pass the quite days

3

So sell yours, buy an NA and with the money you’ve made on the difference, hop over the border into Germany and take it to Komotec :slight_smile: Get the ChargeCooled option too, keeps your intake temps down so you shouldn’t see the power drop off when things get hot. Oh and you can see out the back through the grill :slight_smile:

4

bigger blower, spinning slower, so TVS1320 maybe

5

What air intake boxed did you have? Did everybody have the standard? TRD?

6

I am looking at the TVS1320 upgrade on mine for the same reason, SC whine is a problem for drive by noise :frowning:

7

Sounds like another dose of man maths :slight_smile:

8

changing your car or your supercharger would be insane, get rid of the TRD or get a bigger backbox

my cars pushing 300bhp, runs a TRD and has 2 backboxes for quiet trackdays

9

I’m running a TRD with ITG filter, 2Bular 100cell cat and 8x24 backbox.
So I’m not that surprised that I did not make the 95db limit, but they measured 105db which is on another planet.
The most surprising was that the completely stock Elise SC also got black flagged.

I will not change the car or supercharger, but mabe a new side exit exhaust with possibility to put a 2nd backbox for trackdays is a good idea.
I’m also looking at sourcing some of that trick dampening material that Koenigsegg uses to silence the intake a bit…

10

Nothing wrong with man maths, I’ve justified many of an upgrade with it :wink:

Going to try the drive by at Brands with my extra exhaust box and see if the SC whine sets it off.

11

I’ve not had problems at Brands. I think both of our potential problems are induction, not exhaust

12

That is interesting and good to know, still waiting to hear about the evening session.

13

I have not confirmed this on track yet but my wife told me (without me asking) that “the car sounds different, what did you do?”

What I did was:

  • Repack silencer with acoustafill
  • Cover as much as possible the inside of the rear clam, wheelarch liner etc with something called GLADEN AERO-Foam

It will be another couple of weeks before I know if it worked. As backup I have prepared a 90deg exhaust tip bend to direct the exhaust away from the microphone :slight_smile:

14

Thanks for the tip, had the same kind of Idea, build a intake box in the wheelarc with silencer material. I went from no black flags to 119 (!) dB, on Gelleråsen. No changes on the exhaust side

15

Result - about 50% reduction, 100db vs. 103db.
I’m guessing the repacked silencer did most of that, if not all.

However still waaay off that 95db limit. :imp: