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MG Midget and Sprite Technical - Quietening exhaust slightly for trackdays

Hi all,

Just wanted to know if anyone has any tips for quietening an exhaust by a couple of decibels for track days.

The last track day I went to my midget was VERY borderline, with a lot of smiling and the promise of short shifting down the straight I was allowed to run on this occassion but I don't want to have to worry about it everytime I go to a track day!

I have a 1500 midget with twin 40's and a stage 3 setup including a cylindrical single box exhaust, if I remember correctly the bore is about 1 3/4"

I have tried looking for temporary bolt on tips but all I seem to find is stupid stainless things which are for looks and nothing else!

Does anyone know of a method to reduce noise without reducing power significantly or a product on the market which will do so? Ideally I dont want anything huge sticking out the back of the car but I do want to be able to enjoy the trackdays.

As always any help greatly appreciated

Dave
D Prince

Dave,

I have a SupaTrap which I bought to quieten my sprint Midget but having fitted an MGB rear box I can usually get it through scruitineering round about 101dB.

I am in Sth Glos so if you want to give the SupaTrap a try then you are welcome

John
John Turner (Midget & MGB)

I had to use a similar device last track day, could have been a supatrap too. Fits onto the end of the exhaust and has a series of close fitting plates which dampen the noise. To be honest I didn't feel that much of a loss in power. It did the job though.
Tarquin

you could/should also consider your air filter setup; far more noise emanates from twin weber induction than most people realise...
David (davidDOTsmithAT stonesDOTcom)

What was the circuit and what was the noise limit for the day?
Daniel Thirteen-Twelve

"I didnt feel that much of a loss in power"

Tarq, you cant loose what you dont have... :)
Arie de Best

You can buy a small add-on box that fixes to your tail-pipe; I've seen these one more race-oriented cars on many track days. Most motor-sport companies sell them, e.g. Merlin. They may look a little awkward, sticking out behind the car... but this is a track-day not concours or POO.

Vizard has very rude things to say about the Supa?Trap; remember, it's hard to 'feel' power won and lost in terms of bhp.

A
Anthony Cutler

At my last Sprint, my car came in at 103 db and the scrutineer said that was fine. What is the usual maximum for trackdays and circuits?
Gary Lazarus

Gary there is more than one form of noise test; one is done at the exhaust exit, another is 1 metre away, then some circuits conduct 'drive-by' tests measured at the edge of the circuit usually on the exit of a bend where cars are on full power. So it's not safe to compare different readings unless one knows the type of test being referred to.
David (davidDOTsmithAT stonesDOTcom)

I think that mine was done only from about 1 meter away although I'm not certain as I was sitting in the car at the time.
Gary Lazarus

I've seen cars with a simple solution: a "bend down / sideways" end piece if you know what I mean. Altough deflecting the sound downwards could amplify it I think, but sideways, away from the measuring point is done.
Alex G Matla

Hi Guys,


Thanks for the responses, the last trackday was a at Keevil airfield, the limit on the day was 100dbl, mine came in at 101.7. I realise that this is one of the lower limits but the company which runs these trackdays do quite a few, at several airfields, all within 20 miles or so of me, so I would like to be able to participate.

These readings are done approx 1m from the exhaust at 4500rpm.

David - you're are correct about the induction noise, it's a great sound and noisey in itself, but there really is little I can do with that, due to it being a 1500 with the longtract intake manifold there is no room to fit a K&N box I have had to use individual foam piper x socks cut to length.

Ant - I too have seen these on race orientated cars, I had a scan through merlins website before posting and couldn't spot any, you don't happen to know what to search for to bring them up?

Alex - this was suggested by a racer friend of mine, I think I shall have to buy a noise tester myself and have a play with these!

As I say ideally I would just like to have a backup if I get a scrutineer who's having a bad day and won't let me on track if I have nothing!
D Prince

Hi Dave

I'd give them a ring... I'm sure I spotted at least one supplementary box when I was down there a couple of weekends ago...

A
Anthony Cutler

Anthony C

"Vizard has very rude things to say about the Supa?Trap; remember, it's hard to 'feel' power won and lost in terms of bhp"

I agree but if push comes to shove a few lost BHP is better than no drive.

There are other bolt on silencers but they will also affect output to a greater or lesser degree

Regarding limits, the MSA states 108dB for Road Registered classes. Castle Coombe has a further restriction for MSA sprints to 105dB. Most track days will require 100dB.

The measurement of noise levels leaves a lot to be desired! It is normal to measure 1m away at 45deg from the line of the pipe - revs 2/3 or 3/4 of max. Its unusual for the noise checker to carefully monitor your revs so there is some 'opportunity' there!

John Turner (Midget & MGB)

Get your rev counter to read low! And add a downturn to the exhaust exit pipe.

And as all noise meters are biased towards the higher frequencies, the induction roar/whistle will make a lot of the reading, try draping a rag over the air filters to cut that down, remember to remove rag before getting on the track!

Andy
Andy Borris

I am fortunate that my son makes all of my exhausts for me so I can taylor any sytem I want, however the point I would make is that most exhaust silencers have inside of them a form of wadding. Sometimes as this wadding ages the sound of the exhaust becomes louder and tinnier. Cutting open the can and repaking with new material can have a big effect. Wadding can be bought eqasily at most motorcycle shops as on most 2 stroke bikes it is common practice to repack noisy exhausts.
The only problem is welding the can back up!!

The other thing I would be tempted to do would be to replace your existing silencer with another one that was hopefully longer and better quality.
Robert (Bob) Midget Turbo

I just replaced my Maniflow single box silencer. The old one looked perfect but the new one is definitelt quieter. I think they do deteriorate with age.
Chris H (1970 Midget 1275)

Chris that's a missed opportunity! Kim at MagicMidget sells an excellent repackable silencer in stainless which mates up to the Maniflow systems. If it gets louder you simply unbolt an end and repack the innards with fresh wadding...
David (davidDOTsmithAT stonesDOTcom)

Dave Prince - the Merlin bolt-on isn't a cheap option! But it does a reasonable job and you can take it off again at the end of the day.

Better still, Kim's doing a 1500 system these days so give him a ring on 01225 704257 and he'll sort you out. He's only at Melksham.

Did you ever see the silencer he supplied for my FISC car? Did a great job!

Max


Max max-at-midgetmax-dot-com

I though Kim had such a silencer David but I was not sure.
As I stated above been able to repack an exhaust is a wonderful thing, I would certainly give Kim a bell!
Robert (Bob) Midget Turbo

I had Maniflow supply a larger oval shaped across the back single box - nice sound but not overly loud on runs.
Gives good ground clearance !

Richard.


richard boobier

But the Magic Midget re-packable silencer is large and ugly (in my view)
Chris H (1970 Midget 1275)

i had a magicmidget repackable silencer fitted by the po
filled it when empty and sounded fine but i blew all the dampening out in about 3/4 months of driving
after filling it up 3 times i ditched it and got an rc40 back box
Onno Könemann

Onno I don't understand why that should happen? I've had one on my racecar for 2 or 3 years now and it still passes noise tests, haven't had to repack it yet...
David (davidDOTsmithAT stonesDOTcom)

don't know
it also had a bit of a ratle
as said it had been instaled by the po so it might not have anny thing to do with the quality
Onno Könemann

Thanks for the comments guys,

I know Kim @ Magicmidget well and the irony is my car is the one which Kim used to make the pattern for the 1500 system you mentioned earlier. The exhaust he had made for me has had to be slightly customised from the standard ones he sells to allow for the low ride height and panhard rod which I have fitted.

The system was fitted in feb if I remember correctly and the car has covered about 2500 miles since then so I don't think it should require repacking just yet.

I think a removeable end piece is the way forward and will have to be investigated with a noise tester.

Thanks to all again.

Dave
D Prince

Dave,

Contacted one of the participants in the MG's on Track day a Goodwood 2 week's ago, to ask him what he uses on his K-engined Midget. His came from Merlin, Pt. No. MM-EX-MUFF-4 and is suitable for tail pipe sizes from 1.75" OD up to 2.875" OD. An alternative is from Demon Tweeks, the 'Sound Barrier', for tail pipes from 2" to 2.5" OD.

Both the same size, about 8" long and 4" diameter, and much the same price, just under £50 + VAT + postage.

Richard
Richard Wale

This thread was discussed between 04/11/2009 and 10/11/2009

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