Classic cars forum & vehicle restoration.

[Kleftiwallah]

Good afternoon chaps and chapesses.

I have an exhaust pipe 8' (2.4m ish) long. where along that length should a silencer be installed?

Over to you knowledgeable types. Cheers, Tony.


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It may work in practice, but not necessarily in theory!

[Rootes75]

What is the exhaust to fit?
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Various Rootes Vehicles.

[alastairq]

The silencer [not, in itself, mandatory....but there are maximum lawful noise levels]......is the 'expansion' box......the distance of this expansion chamber , from the exhaust valve, ought to be properly calculated.....this is so that the 'sonic' pressure waves can be bounced back to the exhaust valve, to aid further exhaust scavenging, thus, effectively, allowing the engine to make more power.

The position of the 'expansion chamber [silencer box] will depend on things like, diameter of the main [primary?] pipe, etc.

An internet search will uncover how to calculate the position.....but if the engine is a standard production item, then by copying what the manufacturer did will help.

[Hence, a short straight open-ended pipe can reduce outputs compared to a well-designed manifold and tail pipe?]

Pipe diameter is important too....too easy to go too wide, for example, which can reduce torque, by changing back pressure.

Sometimes the sheer physical size of a car can create an exhaust pipe compromise......noise doesn't always equal power.

[Kleftiwallah]

Good morning Rootes 57.

The exhaust pipes are for the B.S,A.D.W.D. T31.

On the 'original' set-up the exhaust emerges from the front of the cylinder loopes over the top between the cylinders then take s downward swoop to go under the cockpit and along the base of the body. Where it loops over the cylinders there is a 'hot spot' to warm the carburettor.

I'm fitting twin carbs (facing rearwards tucked under the fuel tank) and twin exhausts to go forward from the cylinders then down and under the body either side and off to the rear.



Good morning alastairq,

many thanks for thast informative answer, could you enlighten me as to whereabouts is this calculation for the position of an expansion box?

Also...The I.D. of the exhaust pipe should be the same size as the the exhaust exit hole ?

Cheers, Tony.
_________________
It may work in practice, but not necessarily in theory!

[alastairq]

Google?

As an example only, http://www.mezporting.com/exhaust_length.html

I would ''suggest'' having the silencer as far away from the engine as possible...bearing in mind the presence of any axles, crossmembers, etc that might get in the way?

In other words, some practical limitation might impose the silencer position on the whole exhaust system.

[Kleftiwallah]

Good afternoon alistairq,
I had searched for information, I wasn't being bone idle! I've had it up to here with adverts for bespoke exhausts and systems that look like spaghetti.

I tried all combination of words (with or without " " at each end). I've finally got all the bends and straights I think I need, all there is to do now is to find a decent welder!

Many thanks for that lead. By the way, I worked with a Jock who was adamant that the 't' should be a 'd' in your name!

Cheers, Tony
_________________
It may work in practice, but not necessarily in theory!