Bedford K-series noise: induction, exhaust or both?

[Mankee]

I had a quick search in the archives and via Google, but couldn't find quite what I wanted. I really like Bedford Autodrome (did my first ever proper trackday there about 10 years ago) so don't really want to not go there ever again. I tripped three of the noise meters in a single lap yesterday (first semi-flying lap!) and I'm trying to work out if it's my silencer, indution noise or a bit of both.

 

Exhaust is a 6" silencer and VHPD/SLR 4-2-1 manifold, reading 98.9db static at a bit below 5000rpm. As a comparison, it came up at 98db at Rockingham a few weekends ago, so the readings are fairly consistent. Engine is a just over 200bhp modified VVC-based lump and I set myself a limit of 7500rpm yesterday. Induction is Jenveys, Pipercross dome filter and cutout in bonnet.

 

Driveby at Bedford is always tough at 87.5db. I only just tripped them at 87.6db, but three times in one lap is a bit silly of me really. I'm pretty sure that the ones I set off are on the exhaust side of the track when looking at the below diagram, even though I did give it welly past the meters on the north-west and east circuits:

 

http://i401.photobucket.com/albums/pp97/shimmylasco/cars/bedford_autodrome_large.jpg

 

So my questions are, has anyone been in a similar position and what have they done about it? I think I'm going to go to a 7" silencer first, as it's much easier to swap a silencer than mess around with bodywork, airboxes and other stuff to quieten the induction noise. Especially as my current silencer seems to read higher than what I was expecting.

 

Noise is so subjective as always. It was quite windy yesterday too.

[Jonathan Kay]

Could you borrow one of those additional bolt-on cans for the exhaust and see if that solved it before replacing the silencer?

 

Jonathan

[Mankee]

Hi Jonathan. That's a good point actually, but I'd never considered it for several reasons. I'd like a permanent, fit-and-forget solution, I've seen them strangle engines by their nature, I've had to pick a few up off live circuits when they've fallen off cars and, knowing me, I'll probably forget about it being attached and take out people's ankles/cars in the pit late!

 

They do work though, especially on notoriously loud stuff like Cerberas and VTECs.

[Jonathan Kay]

You know more about them than I do! I was thinking of it as a diagnostic rather than a therapeutic intervention...

 

Jonathan

[Jason Plato]

good big can and an airbox I would have thought.

 

my air box on the 1900K reduced noise massivly and it didnt affect power.

[Shaun_E]

I think you are going to struggle but an airbox and a RaceCo silencer is as good as you will get. With that set-up I used to record about 96db at 5500rpm on my 226bhp K which revved to 8000rpm