Intake noise problems on tracks with dB limits

[liipo]

Guys,

I'm having some problems getting by the noise limits on couple of our race tracks. When measured from the exhaust at 4500rpm, there's no problems, I'm at about 90dB there, but when they are measuring the drive-by noises, I'm clocking at little bit over 100dB and the limits are 95dB. So a little problem here as 4 out of 8 races this season will be held on 95dB tracks.

I'm running a 48mm CF-DTM intake with Lee's filtering setup. Any ideas how to get the noise down about 5dB's? I'm going to try a some kind of a sound reflector in front of the collector/Lee's filtering panel, but would be interested to hear how you guys have come around this problem?

Thanks!

Mikko

[JS154]

Guys,

I'm having some problems getting by the noise limits on couple of our race tracks. When measured from the exhaust at 4500rpm, there's no problems, I'm at about 90dB there, but when they are measuring the drive-by noises, I'm clocking at little bit over 100dB and the limits are 95dB. So a little problem here as 4 out of 8 races this season will be held on 95dB tracks.

I'm running a 48mm CF-DTM intake with Lee's filtering setup. Any ideas how to get the noise down about 5dB's? I'm going to try a some kind of a sound reflector in front of the collector/Lee's filtering panel, but would be interested to hear how you guys have come around this problem?

Thanks!

Mikko

What are you running for an exhaust setup?

Headers?
Center pipe(s)?
Muffler?

Are you certain you are pinging the meter on intake noise?

you can run a Rongineer intake box, that will be very quiet, but you wont gte the same peak power at high rpms as the big carbon airbox.

[liipo]

What are you running for an exhaust setup?

Headers?
Center pipe(s)?
Muffler?

Are you certain you are pinging the meter on intake noise?

you can run a Rongineer intake box, that will be very quiet, but you wont gte the same peak power at high rpms as the big carbon airbox.

Hi,

Header=50/50 BMW, Center pipes=Supersprint with big center muffler and Eisenmann back muffler.

I would rather not to go with a different kind of airbox as I can't afford to lose any hp as I'm struckling already with the the modified e36 m3's on the parts were hp counts.

Mikko

[TR-Spider]

When you hear your car drive by at full power, is it louder from the front or rear?

At 4500 rpm in standstill (no load) your throttle bodies will be almost closed and also the amount of air going through the engine is small, and accordingly the power (where the noise finally comes from).

If it is the induction noise, the snorcel of the airbox is like a trumpet...
then you could try to blank off the path of the noise, i.e. make an additional box in front of the radiator.

I enclose some pictures of the nice setup, which Uwe once made. It is basically a box with a foam filter in the rear, which draws the air behind the bumper. AFAIR, from his short test he reported a significant reduction of the induction noise without power loss.


Thomas

[LeeVuong]

Hi Mikko

M3s are notorious for high intake noise, but I also suspect your exhaust, for which you gave no specs (unless I missed them). The two baffles in your filtering panel already diffuse a lot of the sound wave, but there's a limit to what they can filter. Perhaps you can lower the sound level from the rear now...

[jannmann]

I'm one of liipo's mechanic, and we are 100% sure that intake noise is problem, not exhaust. Other M3 with same exhaust setup, but std manifold have no problem. Also this year we go CF airbox (old was thick GF) and that increase noise..

[LeeVuong]

Other M3 with same exhaust setup, but std manifold have no problem. Also this year we go CF airbox (old was thick GF) and that increase noise..

The big aluminum box absorbs a lot of noise. The AFM s a great muffler. The original air filter is a even greater muffler. Also cam duration will have an effect on intake noise. Many things to consider.

[Mick]

I have a similar intake muffler for my car. It replaces the filter frame and is covered in a rubber dampening material designed for speaker enclosures.

I don't use it often. The last time was when I was at a track that had a ridiculously low db limit of 81db @ 50', I was black flagged and told my car was over 100db. After installing the muffler I was left alone. So I assume it dropped at least 20db. The downside is that, with the bumper in place, it chokes the intake and the car runs rich. Since I very rarely use it I have't bothered to create an alternate map for it.

[liipo]

Thanks for the suggestions guys. Yes, the intake makes much more noise than the exhaust.

Lee, you can find the exhaust info on my second post to this thread.

Thomas, thanks for the pics. The box that Uwe made in front of the snorkel seems interesting and worth of trying.

Here's a short vid shot on the first outing of 2012 demonstrating the intake vs exhaust noise.

http://liipo.idle.fi/webiin/2012-season-intakenoise.wmv

Mikko

[liipo]

I have a similar intake muffler for my car. It replaces the filter frame and is covered in a rubber dampening material designed for speaker enclosures.

I don't use it often. The last time was at a track that had a ridiculously low db limit of 81db @ 50', I was black flagged and told my car was over 100db. After installing the muffler I was left alone. So I assume it dropped at least 20db. The downside is that it chokes the intake and the car runs rich. Since I very rarely use it I have't bothered to create an alternate map for it.

Mick,

Thanks! I think I will definitely try something like that, I'm only in need of dropping around 5dB, so maybe a "lighter" version of yours and Uwe's setup.

Mikko

[liipo]

First race weekend is behind and I managed to get the intake noise under the limit.

Made up a box bit like Uwe and Mick from sound deadening material and that did the trick. I'm a happy camper

Managed to come 1st on both races, so that was good too.

Mikko

[Mick]