How to repack a non repackable silencer.

[Keith Scarfe]

I have just finished this little project that I have been meaning to tackle for a while. I took photos while doing it so thought I would post on here in case anyone else wants to do the same.
My exhaust silencer was not silencing the exhaust much and I suspected all the baffling material had long been blown out of the tail pipe. The noise seemed to be being amplified rather than silenced. Some of the younger generation (as I was once) would maybe like this and celebrate it but I am a little more mature these days and although I obviously love the sound of the twink mine was just too grating especially when trying to drive sedately round town. I was sure replacing it would still give a nice, mellower sound at full throttle but be nicer to drive when not booting it. I have repacked the silencer a few times on my race car and I know this is the case. I hope it will be the same for the lotus and not make it too quiet.
The Silencer on my S3 DHC is the transverse oval box. It is easily removed from the car and can be seen here before I started on it.

I was not 100% certain on the internal structure of the silencer when I started but I guessed it was just the oval can with a straight through perforated pipe. So to get into it the only thing to do was to get the hack saw and saw it in half. First I marked a straight line around about 20 mm in from one side.

Then set to it with the hack saw.

This proved to be a little more difficult than I expected because as the cut went through, the tension in the metal, obviously in there during its construction, meant it started to distort and close up the gap I was sawing making the blade stick. It is also very difficult to hold the thing still without squashing it. I used various woodworking clamps to hold it onto the bench. Once through the outer can, I then continued sawing through the centre perforated pipe. Here is the result.

As expected it was a completely empty void with absolutely no wadding in there at all. Just horribly dirty carbon dust.

To put it back together, my plan was to make a strip of stainless steel the same thickness as the outer can and slide it into the end piece forming a joining face to which I can then pop rivet it together. Same for the perforated tube, so the original pipe will slide into the new outer sleeve. I started off by making some templates out of cardboard.

Luckily we have a fabrication shop at work who made the strips up for me and actually tack welded them in place. This meant I only had to have exposed pop rivits on one side of the join rather than on both as I originally planned.

Assembling it back together I found it was too tight a fit and I couldn?t slide it together. To achieve the required sliding fit, a small hack saw slit down the new strip made all the difference and meant the two halves could slide together. Holes were drilled for 6 pop rivets, 3 each side. I thought this was enough.

[Keith Scarfe]

The new baffling material I chose to use is called Accoustafil and came from here https://furoreproducts.co.uk/exhaust-parts and rather than the old fashioned e-glass is this modern stuff that is assembled loosely and when it gets hot the binding thread melts and it fully fills the cavity. It came in exactly the required size (350mm) for the width and the 1M length was slightly too long (too much to stuff in there) so was easily trimmed using scissors.

It seems very good stuff and was definitely far easier to handle than the e-glass.

In order to help get it into the can, a good tip I found was to wrap it around a cardboard tube from some toilet / kitchen roll. The cardboard tube is then withdrawn.

Final assembly using some Hylomar exhaust assembly paste.

And finally the fully finished article.

I have put it back on to the car and started the engine in the garage but not taken it out for a run yet so not sure what it will sound like on full throttle but it does seem much quieter on idle and light revving. I?ll report back when I take it out properly. Need to wait for some better weather for that.
Hope this helps someone.
Keith.

[richardcox_lotus]

Very good Keith and thanks for the pictures. I recall a similar task undertaken with a Sprint silencer - also with photos - but I'm buggered if I can find the post now.....

Thanks anyway
Richard

[billwill]

Did you think it not necessary to make a short tube to cover the join of the inner tube.

[Keith Scarfe]

Yes Bill the short tube is there to join the inner perforated pipe. Made in the same way by rolling up some stainless sheet. You can see it in the 7th pic down where it is tacked onto the end piece. Look inside, you can see the original pipe.

[Keith Scarfe]

First drive out this year for me today and I can say this is a wonderful job done. I am really pleased. It has definitely quietened it down a little while driving gently (not too much though) but open it up and on full throttle it still makes the lovely twincam sound just a little quieter but much more meaty rounded sound rather than the crackling sharp sound it made before. Also on the over run the horrid moggy minor type farting sound is now a nice burble sound.
Seems to be all sealed OK with no signs of gasses leaking around the new joint which is good. Will see how it is in a few miles time.
Superb. Looking fwd to the drive home now.

[pereirac]

Nice work...

I wonder if you could make a hole at one end and then just stuff steel wool into the cavity to 'refill' the silencer. Not as efficient as your method but simpler. You could then weld a plate over the hole to cover it.

Carl

[Bud English]

That will work if you want a good fireworks show. Been there, done that. Amazing how little heat it takes to start steel wool burning and how fast it goes up and out the tail pipe. In all probability the "welding up" should do it. Admittedly, this was on VW sand rail and my "muffler" was pretty close to the headers, but it was an impressive light show even in daylight .

Thanks to Keith for this thread. Nice to know this can be done without ending up with the high pitched Rice Burner exhaust sounds we all love to hate.

[Davidb]

This project and the very similar project by El-saturn had me interested enough to find out who the distributor is for "Accoustifil" in North America.

The distributors site is:
www.culimeta-saveguard.com

You can purchase directly from them I believe.

[el-saturn]

...................still "in " the car, same as 2000 miles ago: nice and quiet under 2000rpm: city-like! ---- once your "out there": unbeatable TC sound all the way to 7500!! PS certain pedestrians do NOT share the JOY!! and there's a small difference is: i'm using 2" tubes starting at the Y-tube!! ---------------------- more volume more sound

[prezoom]

Thanks David,

I am planning on a pipe enlargement, including the silencer to go along with the Zetec conversion of my Plus2. Currently awaiting the arrival of the exhaust flange, from Dunnell Engineering.

[Quart Meg Miles]

Excellent thread, Keith, which I've only just spotted. Perhaps I just need to put some stuff in the SS box I discarded twenty years ago once my MS unit falls apart. Thank you.

[Keith Scarfe]

Hello Meg. Yes I remember the thread you did a while ago trying to drum up interest in a group buy for MS silencers. I was tempted as mine made a horrid noise and I too believed this was due to the difference between SS and MS. I now think however that the main reason for SS exhausts sounding so much louder is that all the wadding gets blown out of them but they still look new from the outside. It would be interesting to hear what you think to the difference if you repacked your stainless one. It costs relatively nothing compared to buying a new silencer, that was my main reason for trying it. If the above method failed the worst that would happen is that I would have to buy a new one.
Cheers Keith.

[Davidb]

Interesting comment about the stuffing getting blown out. My "other car" had a stainless muffler/silencer from Falcon exhausts of the UK. It was simply too loud so I fitted an American made muffler (Magnaflow) and it was quieter for a while but now seems as noisy as before. A three day rally at eight hours a day is exhausting! (Sorry...) The effect of this is that I now suffer from hearing loss!

[Quart Meg Miles]

Interesting comment about the stuffing getting blown out. My "other car" had a stainless muffler/silencer from Falcon exhausts of the UK. It was simply too loud ....

Hmm, mine was a Falcon and I'll make it a summer project to stuff it as described above.

The MS silencers don't seem to have any filling so it must be about case resonance. I declared, somewhere earlier, that a MS silencer is still unacceptable if the intermediate pipe is SS. But if it is easy to repack them at a few quid a time then that seems to be the way to go.