Exhaust Baffle?

[Roger Dyke]

Hi all,

 

I have just purchased a second hand Irvine 46 mk3 (red one). It's silencer is stamped "1E". Inside the silencer is a cone baffle with a hole at the pointed end. The cone is trapped between the two silencer halves.

 

In parting the two halves, I found the cone with it's narrow end pointing towards the engine. Is this correct, as I was sort of thinking that the pointed end of the cone should be facing the outlet to the rear?

[Engine Doctor]

Try it in both directions a note the best for silencing and performance, Many engines have variations of this and none seem to make a lot of difference. OS used to sell a plate with semi circular punched holes with the tang bit pointing towards the outlet . These really made a difference to noise with only a slight loss of performance.

[Roger Dyke]

Thanks for that, I'll give it a try. My question really was, which way around is the default supplied position as the previous owner has probably moved it.

[Charles Smitheman]

My understanding is that the second chamber should be about 40% of the volume of the first to cancel out the sound waves.

I have made a number of silencer extensions for old engines using this rule of thumb with success.

 

[Engine Doctor]

31 minutes ago, Charles Smitheman said:

My understanding is that the second chamber should be about 40% of the volume of the first to cancel out the sound waves.

I have made a number of silencer extensions for old engines using this rule of thumb with success.

 

Ive done a couple of silencer mods , one on an Enya 40 SS . That worked extremly well . I used the OS type of baffle .

Ive also read somewhere that making a baffle plate  to replace the cone with holes punched through using a punch with four flats ground to a piont leaving the jagged edges works well Has anyone tried this ?

[Cuban8]

19 hours ago, Engine Doctor said:

Try it in both directions a note the best for silencing and performance, Many engines have variations of this and none seem to make a lot of difference. OS used to sell a plate with semi circular punched holes with the tang bit pointing towards the outlet . These really made a difference to noise with only a slight loss of performance.

Yes, they worked very well. I used to sometimes add a further baffle - just an ali disc with a central hole about 25% larger than the silencer outlet and spaced at a suitable distance from the standard punched baffle. Either on the exhaust port side or between the original baffle and the outlet. Experiment to find best position re noise/power. Very effective.

I also made a 'gun silencer' type supplimentary silencer for a Flair Magnatilla that I had at the time. A series of discs with holes of gradually increasing size spaced inside a length of 30mm or so plastic tube (plumbing). Two stroke engine so no heat problem and it fitted after the standard silencer with a length of silicon and a suitable clip to the underside of the fuz. I guess the theory was to gradually allow the gases to expand within the silencer body, rather than escape with a loud crack. It did work well. Some interesting Youtube vids available.

Not my original idea -  I'm sure it was part of a noise reduction project published in one of the several mags that existed 25 years ago or an internet based project. Anyone else remember it? Might have been a Wizard of Oz thing...not sure now.

I did have a print/copy of the articles, but they've gone missing.

Edited October 25 by Cuban8

[Charles Smitheman]

I think it was a Norwegian F3a enthusiast who wrote two articles in a mag in the eighties. I have them somewhere.  Lots of maths boiled down to "about 40%" for the 2nd chamber volume.

He also used further chambers. I have not tried this, as my attempts have been quiet enough anyway. 

Sizes of engines I have tried range from 09 to 60. I am more interested in engines that run well rather than extracting the absolute maximum from them.

 

I have tried various baffle types but not scientifically. Nail holes in soft ally sheet worked too. Important is the overall size of the sum of all the holes. Too small would choke up the engine, too big would be noisy.

 

My first attempts before finding out about the 40% chamber volume were not all successful. They caused power losses and drew remarks about the funny noise! I recently adjusted one of these and it now works fine. 

[Fin 35]

I’ve just purchased a O.S. silencer (E-2030S) to fit to a Thunder 25 GP that was rather noisy with its small unbaffled silencer. The OS silencer is unusual in that it has two cones close together at the front and a more conventional cone at the rear, all pointing to the exit. The front cones seem very restrictive but I’ve yet to run the engine. 

[Fin 35]

Thunder Tiger that is. Just a thought about the direction of the cone - if the point faces towards the engine exhaust, then fluid will tend to collect in the silencer rather than being blown out. 

[Nigel R]

Neat way to get a couple of extra chambers into the standard silencer. Large, tiny, medium and small, in that order. I suspect the restrictions have to start small and increase as has passes, to keep the pressure highest near the engine. I have a similar looking silencer for a 10cc o.s. and it is very effective.