Exhaust too quiet on Beta BD3

[MtB]

Our three cylinder Beta Marine BD3 is a lovely engine to use, modern but attempting to mimic the vintage engine style by being 3 cylinder low-revving with an vertical exhaust out through the roof.

 

Trouble is, the exhaust note is extremely muffled and quiet, virtually inaudible at low crusing speeds and although I prefer quiet to noisy, I'd like it to sound a bit more, well, traditional. So I'm planning to modify the exhaust so we can actually hear it bit more, but I'm not sure exactly how to modify it.

 

First I'll describe our current exhaust system. It's a bit of a bodge. We have about six inches of 2" BSP pipe coming vertically off the manifold, then a 23" long vertical silencer with 2" BSP connections each end. The outlet from the silencer has a 2" to 1½" BSP reducer fitted then there is 30" of Bosal 1½" flexible exhaust tube connecting this to the inlet of the welded-in roof fitting. At the inlet of the roof fitting the diameter steps back up to 2" BSP and there is an elbow, and outside we have a 3" diameter stack about 30" tall.

 

Reading back through the old threads about exhausts it seems a silencer is often not installed on slow revving engines so yesterday I tried an experiment. I dismantled the internal exhaust and temporarily replaced the silencer with a plain section of 2" diameter tube and ran the engine. Very noisy, too noisy by far. I'm wondering if the section of 1½" tube is increasing the noise and whether using 2" tube all the way will make any difference. Any opinions anyone please?

 

I'm also contemplating leaving the structure of the system as it is but cutting a hole in the side of the silencer, hooking out all the stuffing or whatever is inside a silencer, and welding the hole shut again. Does anybody know what is inside a silencer, exactly?

 

Suggestions or advice most welcome.

 

Cheers, Mike

[DHutch]

The first thing i would by asking myself is whats in the silencer!

- Look down it and tell us what you can see, its proberbly got some baffles in it, so you wont be able to see right the way through?

- It may well be double skin too, but if its not and its baffled you can probably see where the baffles are by the weld marks on the outside.

 

If you want a nice noise but without quiet the racket, a straight through silencer is probably they way to go.

 

Whats the course of the flex tubing as well, fairly stright? Sounds like at some point they failed to get hold of any 2" flexable to me.

 

 

 

Daniel

[Malarky]

Check out what's with them fat chromey exhausts boy racers have sticking out of the back of those little cars they drive?

Pick the brain cell of a chav?

[MtB]

The first thing i would by asking myself is whats in the silencer!

- Look down it and tell us what you can see, its proberbly got some baffles in it, so you wont be able to see right the way through?

- It may well be double skin too, but if its not and its baffled you can probably see where the baffles are by the weld marks on the outside.

 

If you want a nice noise but without quiet the racket, a straight through silencer is probably they way to go.

 

Whats the course of the flex tubing as well, fairly stright? Sounds like at some point they failed to get hold of any 2" flexable to me.

 

 

 

Daniel

Hi Daniel

 

Thanks for your answer.

 

I dunno what's inside the existing silencer apart from a lot of dark black soot - that's all I could see when I looked down the ends.... it's re-fitted to the boat now and I'm kicking myself for forgetting to find a torch and look into it carefully while it was on the bank! The inlet and outlet are offest and no, I couldn't see though it. No weld marks on the outside either.

 

The flex tube bends through 90 degrees tand runs horizontally across against the roof to the roof outlet position which is about two feet offset from directly above the manifold outlet.

 

A straight-through silencer is a good idea - know of any with 2"BSP threaded connections?

 

(MUST go to work now!)

 

Cheers, Mike

[Albion]

Our three cylinder Beta Marine BD3 is a lovely engine to use, modern but attempting to mimic the vintage engine style by being 3 cylinder low-revving with an vertical exhaust out through the roof.

 

Trouble is, the exhaust note is extremely muffled and quiet, virtually inaudible at low crusing speeds and although I prefer quiet to noisy, I'd like it to sound a bit more, well, traditional. So I'm planning to modify the exhaust so we can actually hear it bit more, but I'm not sure exactly how to modify it.

 

First I'll describe our current exhaust system. It's a bit of a bodge. We have about six inches of 2" BSP pipe coming vertically off the manifold, then a 23" long vertical silencer with 2" BSP connections each end. The outlet from the silencer has a 2" to 1½" BSP reducer fitted then there is 30" of Bosal 1½" flexible exhaust tube connecting this to the inlet of the welded-in roof fitting. At the inlet of the roof fitting the diameter steps back up to 2" BSP and there is an elbow, and outside we have a 3" diameter stack about 30" tall.

 

Reading back through the old threads about exhausts it seems a silencer is often not installed on slow revving engines so yesterday I tried an experiment. I dismantled the internal exhaust and temporarily replaced the silencer with a plain section of 2" diameter tube and ran the engine. Very noisy, too noisy by far. I'm wondering if the section of 1½" tube is increasing the noise and whether using 2" tube all the way will make any difference. Any opinions anyone please?

 

I'm also contemplating leaving the structure of the system as it is but cutting a hole in the side of the silencer, hooking out all the stuffing or whatever is inside a silencer, and welding the hole shut again. Does anybody know what is inside a silencer, exactly?

 

Suggestions or advice most welcome.

 

Cheers, Mike

 

On Albion, with its Gardner 4LK, I only had an expansion box. The exhaust from the engine ran through a tube into, and right near the top of a tubular chamber (looked like a silencer but wasn't). The roof outlet ran from near the bottom of the same chamber up and out. There were no baffles or wadding in this whatsoever. I've crudely drawn a diagram below, but you'll get the idea. It was fabricated for me by my shellbuilder Graham Edgson of Norton Canes Boatbuilders. Roger

 

Outlet

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Inlet

[ditchcrawler]

Our three cylinder Beta Marine BD3 is a lovely engine to use, modern but attempting to mimic the vintage engine style by being 3 cylinder low-revving with an vertical exhaust out through the roof.

 

Trouble is, the exhaust note is extremely muffled and quiet, virtually inaudible at low crusing speeds and although I prefer quiet to noisy, I'd like it to sound a bit more, well, traditional. So I'm planning to modify the exhaust so we can actually hear it bit more, but I'm not sure exactly how to modify it.

 

First I'll describe our current exhaust system. It's a bit of a bodge. We have about six inches of 2" BSP pipe coming vertically off the manifold, then a 23" long vertical silencer with 2" BSP connections each end. The outlet from the silencer has a 2" to 1½" BSP reducer fitted then there is 30" of Bosal 1½" flexible exhaust tube connecting this to the inlet of the welded-in roof fitting. At the inlet of the roof fitting the diameter steps back up to 2" BSP and there is an elbow, and outside we have a 3" diameter stack about 30" tall.

 

Reading back through the old threads about exhausts it seems a silencer is often not installed on slow revving engines so yesterday I tried an experiment. I dismantled the internal exhaust and temporarily replaced the silencer with a plain section of 2" diameter tube and ran the engine. Very noisy, too noisy by far. I'm wondering if the section of 1½" tube is increasing the noise and whether using 2" tube all the way will make any difference. Any opinions anyone please?

 

I'm also contemplating leaving the structure of the system as it is but cutting a hole in the side of the silencer, hooking out all the stuffing or whatever is inside a silencer, and welding the hole shut again. Does anybody know what is inside a silencer, exactly?

 

Suggestions or advice most welcome.

 

Cheers, Mike

I would like to suggest whatever else you do that you get rid of the 1 1/2" stuff as it could well be restricting your exhaust flow. I think you will find Beta specify 2"

 

A boater on our moorings made his own expansion box from a pub co2 cylinder, it has quite a ring to it.

[nb Innisfree]

Maybe you could find a long drill, one of those long masonry jobs and drill a hole through the baffle(s) from both ends? just drill one to start with and then have a listen before drilling any others.

 

Never done it myself mind, just a thought

[alan_fincher]

Maybe you could find a long drill, one of those long masonry jobs and drill a hole through the baffle(s) from both ends?

In my experience you'll struggle to drill anything at all with a masonry drill that isn't masonry!

[nb Innisfree]

In my experience you'll struggle to drill anything at all with a masonry drill that isn't masonry!

 

Maybe but it's worth a try

[MtB]

Thanks for your replies everyone.

 

Having googled for silencer construction and seen a few diagrams it seems there isn't any wadding or anything to remove. They simply work on the basis of passing the exhaust gas through a series of chambers created with baffle plates which smooths out the pulses. Converting a silencer into a single expansion chamber seems therefore quite straightforward. Just destroy the effectiveness of the baffles by bashing big holes straight through them.

 

 

Maybe you could find a long drill, one of those long masonry jobs and drill a hole through the baffle(s) from both ends? just drill one to start with and then have a listen before drilling any others.

 

Never done it myself mind, just a thought

 

 

Yep, exactly. I'm going to try that, but not with a masonry drill. Like Alan, I too doubt if it will have any chance of drilling steel whatsoever! I have quite a few diamond core drills with extension mandrils in my shed though and I'm reasonably certain they cut though steel perfectly happily. Failing that, I'll sharpen a mooring pin to a nice sharp point and try punching it though all the baffles with a nice big club hammer :-)

 

Cheers, Mike

[alan_fincher]

Maybe but it's worth a try

Not if it's metal you want to drill through, it ain't. They will just spin on the surface util the tip is burnt off. (Honestly!).

 

Even attempting to drill softwood with a masonry bit is a challenge - although if you don't have matches you can start a fire that way.

[furnessvale]

Thanks for your replies everyone.

 

Failing that, I'll sharpen a mooring pin to a nice sharp point and try punching it though all the baffles with a nice big club hammer :-)

 

Cheers, Mike

 

Worked a treat on Alton when I felt she was being choked by the silencer.

 

George ex nb Alton retired

[MtB]

I would like to suggest whatever else you do that you get rid of the 1 1/2" stuff as it could well be restricting your exhaust flow. I think you will find Beta specify 2"

 

A boater on our moorings made his own expansion box from a pub co2 cylinder, it has quite a ring to it.

 

 

I just checked the installation instructions for the engine and it does not specify the exhaust diameter, instead specifying the maximum back pressure measured at the exhaust manifold must not exceed 1.5 PSI. They make no comment on any relationship between exhaust diameter and the sound though....

 

I like the idea of incorporating a CO2 cylinder, but I may not have enough height available. Someone suggested the other day welding a 3.9kg gas bottle in line instead of a silencer. Just so happens I have a few of them behind the shed :-)

 

Will try punching the silencer through with a mooring stake first though. That's the easiest and simplest option!

 

Cheers, Mike

[matty40s]

completely off topic, sorry, but Alan, while you are burning off drill bit tips, nip inside and empty your inbox!!!!!

[ditchcrawler]

I just checked the installation instructions for the engine and it does not specify the exhaust diameter, instead specifying the maximum back pressure measured at the exhaust manifold must not exceed 1.5 PSI. They make no comment on any relationship between exhaust diameter and the sound though....

 

I like the idea of incorporating a CO2 cylinder, but I may not have enough height available. Someone suggested the other day welding a 3.9kg gas bottle in line instead of a silencer. Just so happens I have a few of them behind the shed :-)

 

Will try punching the silencer through with a mooring stake first though. That's the easiest and simplest option!

 

Cheers, Mike

How about an ex fire extinguisher?

[Speedwheel]

Just remove the silencer.

[ditchcrawler]

Just remove the silencer.

He tried that first

[PhilR]

This is an interesting thread. A few people have been asking about hospital silencers and others have asked about sound insulation. Now someone wants to make their exhaust sound louder. (edited)

Edited September 10, 2009 by PhilR

[Albion]

Thanks for your replies everyone.

 

Having googled for silencer construction and seen a few diagrams it seems there isn't any wadding or anything to remove. They simply work on the basis of passing the exhaust gas through a series of chambers created with baffle plates which smooths out the pulses. therefore quite straightforward. Just destroy the effectiveness of the baffles by bashing big holes straight through them.

snipped

 

I'm afraid that simply isn't true. Some silencers can be constructed with labyrinth chambers to stifle the noise (like a multi chambered expansion box, put simply) but most automotive silencers have wadding in them to absorb the noise. When a car silencer starts to break up significantly you can sometimes see evidence of the strands of fibre being pushed out of the outlet pipe.

Roger

[MtB]

I'm afraid that simply isn't true. Some silencers can be constructed with labyrinth chambers to stifle the noise (like a multi chambered expansion box, put simply) but most automotive silencers have wadding in them to absorb the noise. When a car silencer starts to break up significantly you can sometimes see evidence of the strands of fibre being pushed out of the outlet pipe.

Roger

 

 

Hi Roger,

 

Thanks for your diagram in your previous post. I may well end up having something similar made myself. There is a local chap here (altered my rudder) who will be able to do it.

 

Regarding automotive silencer construction, the website I was looking at suggested diesel silencers always used the multichambered method, but didn't say why. I can't find the site again in my history or I'd post the link. It was a massive PDF file. Seems intuitively right to me as I'd have thought soot was quite likely to quickly clog a wadding-filled silencer on a diesel exhaust loaded with particulates. I suspect wadding is only used on petrol engines.

 

I don't find silencers break up on my diesel vehicles. The pipes always seem to corrode through from the inside and break, leaving the silencer boxes always in fine condition. Have you seen fibre strands coming from a diesel engine silencer yourself, or is is only petrol silencers?

 

Cheers, Mike

[Albion]

Hi Roger,

 

Thanks for your diagram in your previous post. I may well end up having something similar made myself. There is a local chap here (altered my rudder) who will be able to do it.

 

Regarding automotive silencer construction, the website I was looking at suggested diesel silencers always used the multichambered method, but didn't say why. I can't find the site again in my history or I'd post the link. It was a massive PDF file. Seems intuitively right to me as I'd have thought soot was quite likely to quickly clog a wadding-filled silencer on a diesel exhaust loaded with particulates. I suspect wadding is only used on petrol engines.

 

I don't find silencers break up on my diesel vehicles. The pipes always seem to corrode through from the inside and break, leaving the silencer boxes always in fine condition. Have you seen fibre strands coming from a diesel engine silencer yourself, or is is only petrol silencers?

 

Cheers, Mike

 

That is possible for diesel silencers maybe (although you didn't specify diesel only in your posting). You are correct that diesel silencers usually last for ages, as compared to petrol, which will be to do with the slightly acidic mix of gas and moisture in a typical petrol system. Catalytic converters also increase the moisture in exhaust these days as can be seen from the moisture dripping from petrol car tail pipes during the warm up phase particularly.

Modern diesels usually have to have a catalysed DPF (diesel particulate filter) these days to achieve the required particulate limits required by Euro IV emissions legislation IIRC. The DPF has to be burnt off every so often so what happens further down the exhaust system when that afterburn is initiated in the DPF I really don't know except that they will have to withstand some very high temperatures. Perhaps a wadding muffled system wouldn't be able to withstand the temperatures also.

I think an expansion chamber system will work well for you, although whether is achieves just the right note remains to be seen.

The chamber for my engine was quite large and my gut feel is that the larger the chamber the more mellow the note. It'll be an interesting experiment but the advantage is that it's very easy to fabricate and should give no problems providing the internal tubes are made so that they can't resonate aganst the body of the chamber; that could cause an annoying resonant frequency rattle at certain revs if it is allowed to happen.

Roger

Edited September 11, 2009 by Albion

[richardf]

TW marine do something they call the Trad Engine Silencer - basically it's an expansion box rather than a silencer. I used one as my engine had a straight through exhaust and it certainly took all the harshness out. It is designed so as not to increase the back pressure. It was about £180 from memory, so much more expensive than some of the other suggestions. TW are a very helpful bunch who do know their subject, it would be worth giving them a call.

[Mick_B]

Why not try your local breakers. Car's have 2 silencers and if I recall correctly thats because they reduce differant frequencies (that doesn't look right!!).

If you got 2 from a car you could see if one of them gives the tone your looking for..

[MtB]

TW marine do something they call the Trad Engine Silencer - basically it's an expansion box rather than a silencer. I used one as my engine had a straight through exhaust and it certainly took all the harshness out. It is designed so as not to increase the back pressure. It was about £180 from memory, so much more expensive than some of the other suggestions. TW are a very helpful bunch who do know their subject, it would be worth giving them a call.

 

 

Thanks for that! I've just had a chat with the bloke at TW Marine and it sounds just the job so I ordered one. At £164 inc VAT and delivery, and a virtually straight swap for my current silencer it's well worth the money to me to save all the time involved in devising something bespoke.

 

I'll post again with results when I've fitted it!

 

Cheers, Mike

Edited September 12, 2009 by Mike the Boilerman

[Night Hawk]

Hmmm....I'd keep it as it is...nice and quiet....and have a small CD player hidden in your back cabin playing a range of engine sounds on a continuous loop....you could have different tracks for different types of engine according to your mood!