G'day,
Has anyone cut open an early Chummy muffler to see what is inside, like how it is/was constructed?

One the outside, does 4" diameter, 23" long body, 1&1/4" inlet pipe and 1" exhaust pipe sound about right?

Thanks,
DG

Hi Dennis,

I have just spent nearly an hour writing a comprehensive reply to your query, and the computer has just deleted the whole f*cking thing. So all I can say is that I got a batch of original pattern silencers made by Dave Phillips at the Seven Workshop, so ask him.

Sorry to be so short, but I'm feeling anti-computer at the moment.

David

Oops, enough said for now!

Thanks,
DG

You can speak to Dave Phillips on:

0044 (0) 1225 868696

or visit the website at

http://sevenworkshop.com/

Hope this helps

Ruairidh

I have asked Davie this very question a while ago, but he does not know but says they where made to an original pattern. Anyone got an old one we can cut up?

Doubt if Dennis' dimensions (4" diam)would fit. The ones I've made in the past were copied from what I believe to be an original and they are only 3" diam by 21&7/8" long. Each end is a dish 5/16" deep and there are three internal baffles similar size and shape. The 1" holes (one in each)in the baffles are then offset to each other so that the gases have a snaky journey to the exit. The flanges on these dished baffles are spotwelded in position to the case from the outside.The hole for the inlet pipe is 1&1/2" diam and the exit hole is 1&1/8"d. The longitudinal "join" in the case is not welded but a "Jam-tin" (overlapping) one. It's too difficult to describe here the brackets on either end (they're different length & shape) and one of them is also stepped. It's perhaps interesting that the mufflers in stock in our Austin 7 Club here are the same as I've described - whether they're ex 7 W'shop or locally-made I'll find out, but if the latter would assume also made from an original pattern. For you Ruby people : the ones I've come across were slightly smaller (2&7/8" diam and 21" long)with of course different mounting because of the extra 6" "gap" in the chassis. I can only assume they were originals. Hope this helps. Cheers, Bill

Just confirming that the mufflers in our Club stock were copied from a very good original and done by a professional muffler firm who did on a jig. The only change from original was the relocation of the line-up of holes in the baffles to decrease the back-pressure shown on their test machine, thus making them more efficient. As one who has had cooked feet as a passenger with standard mufflers in our weather, I suggest that Dennis' larger muffler would present an even greater problem. Cheers, Bill

Thanks Uncle Bill!
That was the "good-oil" that I was after. Just one question though, was there any "stuffing" in the chambers between the baffles, or was the can otherwise empty?

So, if these various mufflers were bult to "original plans", who holds the plans and are copies available?

Thanks,
DG

Fantastic Bill, This is just the information I have tried to get for a long time. Can you elaborate on the positions of the internal baffles along the box and the approximate orientation of the 1” holes with regard to each other? I have a straight through silencer on the Chummy (that I made myself), but I have always suspected that it stops me from getting a ‘clean’ take off from rest. I put it down to lack of backpressure; do you think that this is a possibility?

I've checked with the expert who made the Club mufflers (he sold the Exhaust business many years ago) and he said our Spares Manager is mistaken - the baffles were in fact arranged exactly as original ie - the holes offset to each other. He said it's not important as to the arrangement. He also said there was no evidence (I found none either) of any material inside other than the baffles. (Fibreglass was not used in those days and steel wool would be blown out the rather-large holes). He doesn't think the removal of the baffles or lining-up the internal holes would make any difference to performance. Maybe there's enough backpressure in the crazy path the exhaust gases follow after leaving the block? I do know that no baffles would mean greater resonance, which in turn increases highly the chance for welds to crack and part. The Club baffles are @ 5 1/4" from front, then 5 1/2", then 5", but probably don't have to be exact.I mentioned "jam-tin" folding/joining -I hope you understand. In some countries I think it is called a Pittsburgh Lock. The main body, which starts off as a sheet and is rolled, is not welded along it's length but the butt-ends overlocked & flattened into a join as I hopefully described. I know of no plans available for Chummy mufflers & I doubt the Club would do so, as the huge costs & time to get these projects set up requires the compensation of the sale of the made items. Hope this helps. Cheers, Bill

Just one more point - I forgot to refer to. If you make the front hole 1 1/2" (or preferably 1 3/8"?) the pipe forward will slip over the engine pipe wich is 1 1/4" diam. On the Club mufflers, the forward pipe is 1 1/4" with a sleeve about 3" long over it to do the same thing. Cheers again, Bill

Thanks Bill,Will make one up to your instructions and see how it goes.

Ian

Ref "back pressure"

there is a lot of information around reference exhaust system design . Your mention of "back pressure" is not a term I like , but I get what you are trying to suggest. Exhaust systems were and are designed with a number of factors in mind as I suppose are most motor car components!
I have a very small amount of practtical experience of building and using different proprietery systems/manifolds, and have found that it most certainly is possible to influence the engines characteristics via the exhaust. In fact I would go as far as to say that the exhaust manifold/system design along with the valve timing used is what realy dictates the characteristics of any engine and has been a well studied subject by tuners over the years.

those with a musical ear will be well versed in the subject because all it is realy about is the the sound waves set up in the system (and of course the induction system) musical people will understand resonant frequencys I'm sure. Its not so much "back pressure" more about the differences in pressure (both positive and negative)that occur at different points in the rev range on either side of the combustion chamber i.e induction side/exhaust side. These differences in pressure assist the "scavenge" of spent exhaust and aid the induction of a fresh charge. Perhaps what you are suggesting is that the silencer you have made is influencing these "pressure waves" at certain points causing a detrimental effect?
If originality is not an issue moving the postion of the silencer may well have an effect of somekind, but generally it is the manifold that causes the most influence . Do you run a standard manifold ?

regards

Steve.

Steve's right and verified all that my muffler expert friend explained, but I didn't want to submit a lengthy explanation. (The friend, by the way, made replacement extractors for nearly all the Lamborghinis in Oz to make them perform better, exported extractors of all types to New Zealand, America, Asia including to manufacturers in Japan, so he knows about gaining the most from your engine). It is noticeable that on his '29 Chummy he has an extractor exhaust system with a S.U. But if you're using a standard manifold and carby Ian, the baffles etc in the muffler won't make much difference. Cheers, Bill

Yes Steve,Everythig is standard,and thanks to you and Bill for all your input,the first silencer I made many years ago was causing the front pipe to overheat and gave trouble with the fuel vaporising,It was only after reading an article about modern BMWs warping the heads if a pattern non original exhaust was fitted that made me take a closer look at my system,it was evident from the way the paint had burnt off forward of the first baffle on the box that I had a problem.I then made up a straight through box to the pattern of a period advert in a 1920s motor magazine,this has performed well with no more problems with the petrol but tends to be a bit noisy.

Ian, I seem to recall back in the 60's seeing your RP with a twin exhaust coming out from under the running board, was this a noisy straight through system as well?

Algie