How do I make my Elan a bit quieter?

[Bruce Crowthorne]

I hope to attend the CL track day at Goodwood in May, so as a precaution I popped in to Goodwood this morning (I only live a few miles away) and had the guys do a noise check for me. Bad news is that my car recorded 100dB and the limit for the day is 98dB......

It's an S4 and I have the twin pipe rear box (standard Lotus one) fitted currently.

So how do I make it a bit quieter (even if only temporarily!)?

I also have a Double S brand rear box which I could fit.
Now I don't really want to butcher my Lotus twin pipe exhaust, but I am not so precious about the Double S box.
However, in order to fit the Double S box I will need to find a bit of pipe to extend my existing centre exhaust pipe.

So what suggestions?

Is there anything that I can bolt on to the twin pipe exhaust?

If I want to butcher and pack the Double S box, any idea where I can buy a bit of 41mm exhust pipe with a flare at one end to go over the existing 41mm pipe.

HELP!!!!

[simonknee]

I might have a bit of pipe you can have. I bought some stuff from CN that I did not use but it was not economical to send it back once you take postage into account. I think one of the bits was as you describe but I'll have to dig it out.

[nebogipfel]

I suppose the simplest though not cheapest solution would be a Sprint rear box.

They were quieter, not sure by how many dB?

[prezoom]

Take a good look at your air intake for the carbs. A great deal of the total noise is from there. When trying to meet sound regulations imposed at various race tracks associated with SCCA racing, we found the intake was a huge contributor. Open trumpets on Webers are very noisy. Even the difference between individual K&N type filters and the original air box is noticeable. It's far easier to quiet the intake than the exhaust.

Rob Walker
26-4889

[vernon.taylor]

Salut Bruce

If you need a bendy bit of tube then this is a possibility:

http://www.flexiducting.co.uk/metal_hoses_17.html

They have all sorts of sizes and it's easy to clamp. If you need ends with two different diameters search eBay for flexible exhaust and you'll find companies that offer the end diameters you need.

@+

Vernon

[twincamman]

One of the first tracks in Michigan that required mufflers found the cars went faster with some back pressure . I t stopped the scavenging at the valves and created some horse power - --ed

[Spyder fan]

Hi Bruce,
Neither of my cars will pass the Castle Combe noise test without an additional track day silencer such as the one in the following URL http://www.demon-tweeks.co.uk/motorsport/universal-exhaust-silencers/custom-chrome-racing-sound-barrier
The +2 zetec puts out 102DB static (4500rpm at 0.5M distance) which is fine for most track days at Brands, Snetterton etc, but Combe has almost legendary Nimbys living nearby and therefore the local council restricts the noise on non race days to 100Db static, which for at least 90% of road cars is easy to achieve, but as you have found, the twin tail pipe setup on the Elan is particularly "Fruity" between 4 & 5 k revs. Changing to your Double S single outlet box would be the way to go and as a precaution buy one of the additional silencers as detailed above. What I generally do is to go to the noise test with the silencer naked, see if I pass okay, and if not fit the additional silencer and test again. the guys testing are generally helpful and will let you pull to one side and snick on the extra silencer before testing you again, so you don't have to go to the back of the queue. Merlin Motorsport at Castle Combe will happily sell you an additional silencer on the day, but having a captive market means it will cost about ?80, so best to be prepared beforehand.

The additional silencer for my +2 reduces the noise by 5DB which is plenty ( every 3DB is a doubling in noise) and as Ed points out it doesn't necessarily rob the engine of any power and can in some cases improve things.

I haven't had my S4 tested yet, but it sounds very interesting at 4500rpm so I have bought a tail end silencer for that in anticipation.

If you go through the noise test with an additional silencer, don't be tempted to remove it before going out on track as the marshalls will have noted on your noise pass sticker and you will get black flagged.... end of track day .... no refund.

I look forward to seeing you on the day, I will be the bloke with the 2 cars pictured below with a stupid grin on my face.

[Bruce Crowthorne]

Thanks for all the replies.

Simonk - Brilliant! Any chance you could measure the outside diameter of the non flared part of the pipe for me? I live near Portsmouth, but I will arrange some opportunity to collect it if it is the right thing.

Spyder Fan - I thought for a minute I had hit pay dirt! Demon Tweeks keep nearly what I need. But they list it as 1 3/4 pipe. Now my pipe is 41mm od and my guess is that is 1 1/2 pipe.
Although I could easily be wrong and would love to be corrected!

Pre Zoom - My guess is that it is mainly exhaust. I run the Webers with the standard air box with the duct and air filter in the nose. I am sure that the induction does contribute a bit, but under the static noise test conditions the car is on a fairly small throttle opening to maintain the 4500 rpm.
Now on full throttle acceleration I am sure even my modest induction set up is pretty noisy, but thank goodness that isn't what they are testing!

Regards
Bruce

[Spyder fan]

Assuming you are looking at the bolt on silencers and not the steped connection tube, 41mm = 1.61 inches, not far short of 1.75 inches. Generally you cut a couple of slots into the connecting tube of the bolt on silencer to allow it to be compressed slightly and use an exhaust clamp to fix it to the existing silencer outlet. You don't have to be gas tight here, it's not an MOT, but an exhaust bandage will do the trick.