Best noise reduction

[Supersprint1988]

Due to increasing demands on noise reduction on our Danish tracks I'm preparing an "additional rear silencer project".

Car is a 200bhp Zetec with a large Raceline silencer. I'm planning a set up like this here or this here and here

In the first example there is one large diameter silencer, and in the second there are two small diameter silencers.

What option will give the best noise reduction *confused*

 

Cheers *wavey*

Carsten

 

Edited by - Supersprint1988 on 16 Aug 2013 16:54:12

[Pezky]

How noisy is your car?

 

Mine, with the same set-up was 94db. Have you also considered induction noise?

[Supersprint1988]

Induction noise will be taken care of as well.

 

Danish track do the sound pressure measurement in a different way, so we can't compare

( did 106dB drive by @ 7200rpm )

The Raceline silencer is new and I believe it does what it is supposed to do. Just need to make the car even more quiet.

[rj]

Carsten,

 

 

The most effective way to silence the car it to turn the key you'll find under the steering wheel anticlockwise. By doing so it'll only be around 72dB on drive-by depening on tyres.

 

[Supersprint1988]

Hi Regin

 

Your suggestion might be closer to future dB limits than you know I'm afraid 😔 😔

[Grim Reaper]

Just out of interest, what IS the beautiful part of Denmark?

I'm passing through in a couple of weeks time (in the Seven) and wouldn't want to miss it. 😬

[k.russell]

Hi Carsten

It is my car in the first set of pics, I have a 2L vx engine, the car was very quiet with the extra silencer, I recall 87 db at Caldwell park with air box as well, with just the side exhaust it does around 96- 98 db at 5000 rpm static, but did go over the 98 drive by at Donny. I did eventually remove the silencer as it meant I had to run quite high, the tube under the chassis is the problem, I have fabricated an oval tube to revisit the idea at some stage. Ps the air box build is also in my photo albums.

[Supersprint1988]

Hi

An oval tube under the chassis it must be, no doubt. I think RJ has that oval tube in his set up ( pics 2-3 ). Believe he told me once that even an oval tube can be troublesome though 🙅🏻‍♂️ 🙅🏻‍♂️

[rj]

Carsten,

 

I know. Noise is an issue to me too. More than you think.

 

The lowest tube it at present worn through and therefore leaking It has to be welded before next trackday. The tube is not oval though.

 

Edited to add that I at Fladborg Mark have been measured to I think it was 104dB with this setup. The key issue is that when I enter the long straigt at full welly the induction points directly to the noise meter. Also on the non-Duratec cars the exhaust points towards the meter. Not good for us. You can turn the exit to point either to the ground, inwards or backwards. Anything will be better. I also think an airbox with a 90 degree bend facing downwards would be a benefit.

 

Edited by - RJ on 16 Aug 2013 20:14:52

[gundersen]

Trouble is, that while drive by lift off have been a good solution at Padborg Park for some time, they are now banning cars just for "sounding too load". Even if we don't trip the meter (singular).

That said, I got a 107dB at the meter on the first run, so that might be why they had an extra eye out for me the rest of the day.

[Birkin S3 ZA.]

Hi Carsten,

The longer perforated tube the gases have to pass through the more the sound will be absorbed.

The double pass rear silencer will make it quieter than the single pass one, the larger the perforated tubing diameter the less sound will be absorbed.

 

I would not go smaller than 2" bore and no bigger than 2 1/2" on either silencer, you could also fit one of the different removable outlet restrictors that are available on the single pass silencer.

If the packing is done correctly it would give you a very quiet exhaust, then you could run over a marshal without them hearing you coming 😬 😬

Chris.

[Supersprint1988]

Hi Chris

 

It would certainly boost my street credit at the race track if I could hunt down a marshal 😬

 

It makes good sense that the longer the perforated tube are the better, but there must be a reason for diameter of the 7" silencer most of us drags along with the Seven.

 

Also, on RJ's setup (pics 2-3) the bore decreases after the primary silencer ( something about the exhaust gas being cooler at this distance from the engine )

 

Edited by - Supersprint1988 on 19 Aug 2013 14:17:30

[k.russell]

 

Edited by - k.russell on 19 Aug 2013 20:52:31

[k.russell]

[k.russell]

[k.russell]

 

Edited by - k.russell on 19 Aug 2013 20:56:40

[k.russell]

this project hasnt moved for a while, i have fabricated an oval tube to replace the round (2 1/2") i have calculated this to be the same in area, cannot be done by just squashing the tube as the area reduces. have made a oval to round transformer for the ends to get bends onto oval section. the bit where the side exit joins is a bit of a tough one as the oval tube needs to have a slight bend in it before coming up to meet the transformer. I am sure a small diameter ali,carbon or tit silencer across the back will still have a good effect of reducing the noise. The big silecer i had on the rear before was heavy!

[rj]

Quoting k.russell: 

 

Edited by - k.russell on 19 Aug 2013 20:52:31

 

Trouble with that is that it reduces flow a lot in spite of having the same area. You more or less just "use" the area in which a circle can be drawn. In this case I'd expect that to be two circles, but you still loose a lot.

[rj]

Oh,

 

The R500K rear box weighs around 10Kgs

 

Not good for a weight watcher like myself

[Birkin S3 ZA.]

Hi Carsten, The reason for using a 7" canister is it gives you a bigger distance from the tube to the canister for thicker packing.

 

You can also get some perforated tubing with a lot more holes in it for better sound absorption.

 

I use a 2 1/4 system with a 20" long silencer with a 4" canister on my zetec and most people at the race track tell me its to quiet.

 

One other thing that can cause the exhaust sound to be louder is the cam timing, the further the exhaust cam is advanced the valves will open sooner and let a bigger pressure wave exit the chamber.

But its not one of the things I would not recommend trying to change, just something you can consider when you are planning to build a new motor.

 

Chris.

 

Edited by - Birkin S3 ZA. on 19 Aug 2013 21:19:52

[k.russell]

So would there be a formula to match the flow rate to that of the 2.5" tube ? the tube is completely bespoke so could I just make it the same height at a greater width, as an example if it was twice as wide as it is now, it must somewhere between these sizes have a similar flow rate, perhaps, exhausts are very magic as we know as very few seven designs have an optimum set up to accommodate the cars size and design. It is very difficult to get to the back of the car with large exhausts and nice low ride heights. It could be done by intruding into the passenger boot area though .

RJ the weight thing was more to do with it hanging on bobbins at the rear of the car, my car is not light, it has a boat anchor engine 😬 and me as the driver

[k.russell]

A quick google search suggest that flow rates may be better/ greater with oval over round for a given cross sectional area

[rj]

Quoting k.russell: 

A quick google search suggest that flow rates may be better/ greater with oval over round for a given cross sectional area

 

That sounds very strange. Every flow engineer I've ever spoken to has suggested that it reduces flow.

 

That be air, water and even plastic.

 

 

[gundersen]

Quoting Birkin S3 ZA.: 

One other thing that can cause the exhaust sound to be louder is the cam timing, the further the exhaust cam is advanced the valves will open sooner and let a bigger pressure wave exit the chamber.

But its not one of the things I would not recommend trying to change, just something you can consider when you are planning to build a new motor.

Now that sounds interesting...why don't you recommend changing it? I would think that it would be quite easy to do the experiment if verniers where fitted. Can't valve to piston contact, which I presume is the most imminent danger, be checked by turning the engine over by hand?

[Jonathan Kay]

Quoting Grim Reaper: 

Just out of interest, what IS the beautiful part of Denmark?

I'm passing through in a couple of weeks time (in the Seven) and wouldn't want to miss it.

Are you putting in a lower ratio final drive for Møllehøj?

 

;-)

 

Jonathan

 

Edited by - Jonathan Kay on 20 Aug 2013 11:02:50