Scorpion Autopsy - Update 26:04:2008 - It Lives Again!

[StuBeeDoo]

Some of you may remember I fitted a second-hand Scorpion back box on my Touring and took it off again a week later as it was illegally noisy.
I noticed when I took it off my car that the skin was stamped "11-97". I assume this is a datestamp and therefore the box is over 10 years old. I did offer it for sale, but withdrew it when it was confirmed that it was too loud for road use.
As I had nothing to lose, I decided to open it up and have a look inside. Here's what I found.....



The darker bits of the packing were nearest the perforated pipes. I had to chisel the packing away from the pipes, it had got that hard. Basically, the packing had got so hard/clogged that inside (what should be a) silencer was nothing more than a pair of plain pipes.

This shows the perforated pipes after the packing had been chiseled away.....



Until I started beating hell out of the skin to get inside the box, the whole thing looked fairly good - which was why I bought it.

I just thought I'd share this with you all as I don't like people (least of all me) getting caught. If you want to buy second-hand, make sure you hear the thing first - don't do what I did and buy it on looks alone.

[wackiacki]

cheers fella,got a touring myself and looking for a better system.was that a 2.5 box?

[pnd]

these are known for failing internally and this is a timely warning for those who are attracted by the seeming bargain of second hand parts they are sadly often knackered.

[StuBeeDoo]

Yes. The Sept. '87-on rear boxes are all the same on the 6-cylinder cars.

[BMJG]

can this not be repacked and rewelded now you have opened it up and empty'd it ???

[Simon13]

can't believe you did that!

Can i buy the tail pipes off you?

[DanThe]

I bet with a 24v engine it wouldnt sound half as bad, M20's are noisy antisocial things with standard systems, my Scorpion back box was 18 months old when I fitted it 2 years ago, middle box was brand new, 50,000 miles + later it sounds as good as ever

On the other hand, mate's 325i sounded horrendously loud when he fitted his, so bad he sold it 2 weeks later!

[SPIROS]

buy some exhuast wadding off ebay re-pack box & weld it back up, ive done that on that before on the centre box of my saxo vts its fine sounds good again now

[jimthejunior]

Can you just clarify who told you it was illegally noisy and what calibrated db meter was used to test said vehicle? To my knoledge the there isnt a decibel limit to be enforced.

[StuBeeDoo]

can this not be repacked and rewelded now you have opened it up and empty'd it ???

That's the plan.

Can i buy the tail pipes off you?

No, sorry Simon - it's going back together.

Can you just clarify who told you it was illegally noisy

3 MOT stations.

[Simon13]

i'm sorry but a back box on its own won't fail an MOT for being too noisey! ALL the sound on an M20 comes from the centre box not the back boxes

[jimthejunior]

Can you just clarify who told you it was illegally noisy

3 MOT stations.

So what db meter's were used to test this? And what is the maximum legal limit then?

Im interested as a police officer told me there is no actual limit to be enforced. As in there is no number to be tested against.

[jmc330i]

Im pretty sure there is no specific legal limit, although I think the SVA test limit is 101db.
IIRC, its down to the copper or MOT testers discretion at the time. If a copper thinks the noise is anti-social then you will have a problem, similarly if the MOT tester thinks its too loud, he can refuse to test.

[Simon]

i'm sorry but a back box on its own won't fail an MOT for being too noisey! ALL the sound on an M20 comes from the centre box not the back boxes

I will have to dis-agree with that. When I first fitted the sebring to my 1st sport (6 years ago now!) it totally changed the sound of the car. This was with a standard centre.

I recently had the same set up on my touring, and updated the centre section with a sebring centre, and I was quite dissapointed as the noise didn't change at all.

I did however once fit a knackered scorpion centre combined with the sebring back box, and that did change the noise (that hollow howl) but the pipes were cracked so didn't stay on for long.

[StuBeeDoo]

ALL the sound on an M20 comes from the centre box not the back boxes

Care to explain then how when I fitted the Scorpion it was no different to having no back box? (Yes, I did try it before I put the original back box back on)

its down to the copper or MOT testers discretion at the time

Preeeecisely. I was concerned that the car wouldn't pass an MOT with the Scorpion as it was. I asked the opinion of 3 testers and they all said they would refuse to test it as it's too noisy. Refusal = MOT fail. MOT fail = non-legal car.
Hence my decision to withdraw my offer to sell the Scorpion. I wouldn't want to sell any part that could potentially cause the buyer problems.

[StuBeeDoo]

Can you just clarify who told you it was illegally noisy and what calibrated db meter was used to test said vehicle? To my knoledge the there isnt a decibel limit to be enforced.

I've been trying to find this ever since I opened this thread. Thanks to Brian for posting it on another thread.

Depends on the mood the tester is in. This is the relevant text from reasons for rejection: b. a silencer in such condition, or of such a type, that the noise emitted from the vehicle is clearly unreasonably above the level expected from a similar vehicle with a silencer in average condition.

[StuBeeDoo]

I 'phoned Scorpion and although they were very helpful, they won't repack it for me as I didn't buy it new.
I've sourced a 2kg pack of packing (good old eBay).
I'll report back when it's all done. While I'm stripping it out, I'll try to catch all the carbon so that you can see what's caused the excess noise problem.

[Morat]

I know someone with an MOT on a car that produces 111db and is therefore banned from most tracks, including the ring!

[StuBeeDoo]

I finally got 'round to completing the autopsy today.
This is what the box looked like when I cut the skin open. As you can see, the packing furthest away from the pipes is as clean as the day it went in.



Pulling the packing away from the pipes, revealed this.

The material round the pipes is brittle and full of carbon. At this point, I used 2 stoppers to block the ends of the pipe with the packing still around it and pressurised it with a bike pump. The pipe was virtually gas-tight. That will be why the exhaust was so noisy then. The perforated pipe you can see in this picture has been wirebrushed and the holes cleaned-out with a piece of wire (takes ages!).

Below is just some of the offending carbon - the wind took a lot of it, and some got caught in my particle mask. The level of the carbon dust in the jar is at about three-and-a-half inches.

So now I just need to get the new packing in there and Johnna to weld it back together for me.

[StuBeeDoo]

I've been down to Johnna's today and he's now in the process of welding the skin back on.
The box is now full of lovely new packing. Fingers crossed then......

John's got a pic or 2 on his phone - hopefully he'll post them up.

[jaistanley]

What did you pack it with? Fibre glass or stainless wire-wool?

[Greeny]

There is no legal noise limit, it is at the MOT testers discretion and even if it is excessivly noisy it only becomes a problem if it is anti-social ie. revving the knackers off the car in a built up area at 12.00 o'clock at night.

[jaistanley]

You need a nice MOT guy like wot we used to have in Cov.. I know a sound MOT guy in Witham but I don't know how far I'd like to try his patience..

You'd still have to like the noise yourself even if I handed you an MOT slip tomorrow; and I have an idea you're like me.. I like a bit of a sporty noise, but one that sounds like you're going faster, not like the local chavs are going to give you two inbred thumbs/opposable toe's up! lol

[StuBeeDoo]

There is no legal noise limit, it is at the MOT testers discretion and even if it is excessivly noisy it only becomes a problem if it is anti-social ie. revving the knackers off the car in a built up area at 12.00 o'clock at night.

As above, 3 testers weren't happy with it - they can't all be wrong.
The amount of carbon I removed from the tube perforations made the silencer useless. The system was effectively centre box only. I did a 140 mile round trip and by the time I got home my ears were ringing and my head spinning. It's the only time I've ever been really glad to get out of the car. Even without the testers opinions I couldn't have lived with it as it was - I do too many long journeys - It was bad just on my 9 mile drive to and from work.

This here is the packing that's gone into the silencer.

Mind, it won't carbon-up anymore..... LPG is carbon-free!

[johnl320]

Do you know what state the last engine was in that the exhaust came off Stu? Might have been made worse by a lump burning more oil than petrol like my last E28

john

[StuBeeDoo]

Do you know what state the last engine was in that the exhaust came off Stu? Might have been made worse by a lump burning more oil than petrol like my last E28

No I don't John. The box came from a breaker through eBay - no idea why the car was being fragged.

I have to say though that for a 10+y.o box, it looks really well.

[jaistanley]

LPG isn't carbon free is it??

Surely it's still a petroleum distillate and therefore made of long chain carbon atoms?

Definately burns clean though so I'll stop being nerdy...

[barryj]

I think the problem is here that the MOT tester will not put his name to somthing he isnt happy with, hence refusal to test. You cant blame them really can you?

[stonesie]

On LPG, i serviced a dual fuel volvo a while back and the owner said that he ran it on gas as much as possible.

One of the daft little things i noticed was that the exhaust tailpipe was clean as a whistle inside, another was that the oil was very clean to say it had been in there for a year, after a road test of less than a mile on petrol the tailpipe was black inside

[StuBeeDoo]

On LPG, i serviced a dual fuel volvo a while back and the owner said that he ran it on gas as much as possible.

Anyone who has a dual-fuel car will be exactly the same. Once you convert to LPG, having to put petrol in hurts with a capital H.

One of the daft little things i noticed was that the exhaust tailpipe was clean as a whistle inside, another was that the oil was very clean to say it had been in there for a year, after a road test of less than a mile on petrol the tailpipe was black inside

Normal LPG characteristics.

[Jeepster]

I know someone with an MOT on a car that produces 111db and is therefore banned from most tracks, including the ring!

Interesting, I've never been DB tested at the ring, is this a new thing?

[handpaper]

No, there's always been a noise limit - 95dB @ 2/3 revs, static.
It's not normally strictly enforced, more often it's used to get rid of knob jockeys revving up in the car park, but I did see a standard Ducati 996 turned away last year!

[Morat]

I don't think he was actually tested - he just got a big NEIN at the gate. 111Db is stupidly, obnoxiously loud.

[StuBeeDoo]

I'll be collecting the reborn Scorpion from Johnna's on Friday evening and re-fitting it to the Touring on Saturday.
Will it be coming back off a second time???????????????

[Simon13]

no