[ROVERNET - UK] exhaust and back pressure

John Atkin john at atkin4174.freeserve.co.uk
Thu Aug 12 00:18:29 BST 2004

All mufflers/silencers restrict the exhaust flow to some extent but the
least resistance is with a straight through one but it's a bit noisier and
may not be legal in some places. When I had a motor-cycle , I and all my
friends used to drill out the baffles in the silencers to make more noise
and give a better top speed.
best wishes
John Atkin(IOW.UK)
----- Original Message ----- 
From: "Gundry, Kenneth" <KG at dolby.com>
To: <rovernet at lyris.ccdata.com>
Sent: Wednesday, August 11, 2004 9:51 PM
Subject: RE: [ROVERNET - UK] exhaust and back pressure

Dear Peter,

Thank you for that suggestion.  I hadn't thought of a constriction that
might have developed; I was merely wondering whether the muffler (see, I am
bi-lingual) was unsuitable.  Actually I don't think it is very likely that
it has fallen apart inside, in that my cousin installed it only a few years
ago, since when the car has not done more than a few thousand miles, if
that, and has not been exposed to the elements.  The outside of the exhaust
system is not seriously rusty.  However, I have no idea of the source or
construction of the muffler, or how my cousin chose it, so I really have no
idea whether it was suitable.  I doubt if what he replaced was the original,
in fact, I'm sure not, so he didn't have anything authentic to match.

Anyway I am still interested in whether there is any objection to or
possible damage from disconnecting the exhaust pipe from the manifold
(temporarily, of course) to see whether a reduction in back-pressure
increases the power output.  If disconnecting it makes no appreciable
difference, then clearly there is no point dismantling it.

It occurs to me alternatively that disconnecting the exhaust pipe and
somehow measuring the pressure required to force air through it might tell
me something, except that I really have no idea what the figures ought to
be.  Presumably the actual exhaust gas flow rate is related to the engine
displacement and speed.  I suppose there is some standard form of
measurement for the obstruction to flow and for the sound-reducing
properties of mufflers.  Does anyone know how the performance is specified?

Ken G, 1925 Rover 16/50 (San Francisco)

-----Original Message-----
From: rovernet-bounces at lyris.ccdata.com
[mailto:rovernet-bounces at lyris.ccdata.com]On Behalf Of
sspmilr at netzero.net
Sent: Wednesday, August 11, 2004 9:42 AM
To: rovernet at lyris.ccdata.com
Subject: Re: [ROVERNET - UK] exhaust and back pressure

Hi Ken G:

Your muffler may have rusted to the point where there is
bits and pieces restricting the exhaust flow.  Take the
exhaust appart as best you can, put a cardboard box on
the floor with a flat piece of wood in the box.  Bounce
the exhaust pipe on the wood, as well as tapping the
exhaust with a rubber mallet.  This should dislodge any
bits and pieces from the system.

Hope this helps.

Peter Miller
Port Orchard, Wa.
Formally of South San Francisco.

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