Adding an extra silencer

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James k
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Adding an extra silencer

Post by James k »

Hi,
I took my Traveller out the other day on a good drive for the first time since last September (due to family health issues) and was reminded of how deafeningly loud the new exhaust is. It's tolerable at 30mph but at 60 or 70 it's absurdly loud, I had to virtually shout to talk to the passenger in the car. I'm wondering what can be done about this and am thinking of either fitting a new twin-box exhaust system or somehow adding an extra silencer. Has anyone tried doing this and had any luck? If so, what was involved?

Thanks,
James
TDV102
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Re: Adding an extra silencer

Post by TDV102 »

Probably not loud outside the car though. Resonance issue? My GT-Four was the opposite - quiet in the car but readily woke the neighbours and occasionally set car alarms off! I'd swap for an alternative brand system.

As a footnote, my 55 lost it's back box on a trip up the dales once and I ran it with no silencer for weeks - crisp but not unduly loud.
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Monty-4
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Re: Adding an extra silencer

Post by Monty-4 »

Baffled exhaust tips can make a difference as well as or instead of adding silencers. Certainly calmed my 1.5" twin box system down.
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kennatt
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Re: Adding an extra silencer

Post by kennatt »

whats not widely known or understood (including by me) is that the design of the exhaust contributes to the performance,changing the distance the gasses have to exit,or adding resistance in the form of baffles,can upset the system,
Not sure if this applies to 50 and 60 cars,but probably original systems are best left alone

Its something I read about years ago,someone will no doubt be along to explain the science behind it .
philthehill
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Re: Adding an extra silencer

Post by philthehill »

Kennet
You are right that the design of the exhaust manifold and exhaust system has an impact on the way the exhaust gasses exit the engine.

There is a good description of gas flow and exhaust system design requirements in Vizard's book 'Tuning The A Series'.

You can have good flow and low noise with the right system.

50's & 60's production cars had little in the way of performance silencers mainly incorporating off the shelf silencer components that would silence the engine and as importantly fit under the car in the space available.

BMC sports cars using the 'A' Series had slightly better exhaust systems as regards flow but could be noisy.

A period performance mod for the Minor was to fit a MG Midget/Sprite 1098cc silencer which gave a slightly better performance.

My first competition 'A' Series engine was not fitted with any silencer just a straight through pipe off the LCB exiting at the rear of the car and what a lovely noise it made. 8)

Phil

IslipMinor
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Re: Adding an extra silencer

Post by IslipMinor »

Typically fitting a second silencer at the rear of the car will quieten the exhaust, and make it less 'raspy' as well, BUT you will lose the Minor 'signature sound' on the overrun though!

Our 1380 engined Minor has a big bore LCB manifold feeding into a 2" diameter system, with 3 straight-through Jetex silencers - one small round one up by the manifold, an oval one before the rear axle and another oval after the rear axle, at the side of the fuel tank. The result is a deep, but very unobtrusive burble at low engine speeds, which remains unobtrusive up to around 5000rpm. After 5000rpm the exhaust noise increases noticeably, but is never raucous. It has been measured a number of times for track days at Goodwood at ~89db, so passes the circuit sound limit of 95db quite comfortably. The first iteration of the system did not have the small front silencer, and we had a noticeable exhaust drone at around 3750/4250 rpm - typical motorway cruising of 75/80 mph when not in the UK! The Goodwood noise test was also quite close to their limit.

At normal road speeds of 60/70mph (3000/3500 rpm) the only real noise is wind (with either the hood up or down), with neither the engine nor exhaust being very noticeable.
Last edited by IslipMinor on Sun May 13, 2018 4:19 pm, edited 2 times in total.
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James k
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Re: Adding an extra silencer

Post by James k »

Thanks for the replies!

Monty, What sort of baffled tip are you referring to? Would it not also affect the air flow and engine performance?

In terms of resonance issues, are there any common fixes to sort that out? It's worth noting that the exhaust doesn't even clear the bumper. I wonder if a tailpipe extension might reduce the noise a bit.

Thanks,
James
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Monty-4
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Re: Adding an extra silencer

Post by Monty-4 »

My "baffled" tip is made by HJS and cost all of £9. Imagine a normal chromed tip with some razor blades stuffed in (watch your fingers!).
tip.png
tip.png (12.55 KiB) Viewed 1394 times
Adding any kind of silencer to an existing system is going to effect the potential throughput of the gasses in one way or another. That said, how often do you take your engine to above, say, 3500rpm? I don't think it's going to make much of a difference unless you're screaming about.

Stuffing the boot/back full of blankets or soundproofing it helps too, I suspect it acts as a kind of drum. Also check you're not running too lean or rich as that'll change the sound too. :)
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James k
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Re: Adding an extra silencer

Post by James k »

I fitted a tailpipe extender yesterday. I haven't driven it on a fast road yet so I don't know how much of a difference it's made there but it seems to have quietened down a little bit. It's not making any classic Morris Minor noises any more either :-? It's certainly stopped exhaust coming into the car though which is a big plus. I'm now looking at various ways to reduce the sound and have started a thread in general discussion.

Thanks,
James
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