Exhaust Pressure sensing

[Hugh Keir]

Craig,

I have measured back pressure with this system, and used a length of copper
brake pipe from the exhaust bung which I then pushed a plastic pipe over
that led to the gauge.

I used the same bung that my exhaust temperature sensor normally sits in and
measured the pressure at the wall of the exhaust.

I had concerns that the venturi effect would be reducing the recorded
pressure, but also felt less inclined to insert a tube into the gas flow as
this would have disturbed the flow.

Hugh
----- Original Message -----
From: Craig Dotson <crdotson at vt.edu>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, February 20, 2002 5:46 PM
Subject: Exhaust Pressure sensing


I have searched the archives trying to pick up good ways to measure exhaust
backpressure.  I have found references to welding NPT bungs and Swagelock
fittings onto a header, and this sounds practical.

The questions I had which I have not yet found an answer to in the archives
(there are a lot of them) are:

What type of pressure sensor is capable of surviving exposure to exhaust
gases?

Is there some way of measuring with a pitot-static probe, to get both
dynamic and static pressure?

Does the NPT tap/Swagelock setup measure solely pressure at the tube wall of
the header or does it protrude into the center of the tube?

Which pressure is better to measure, wall pressure or pressure at the center
of flow?

I will be attempting to measure exhaust backpressure on a restricted, fuel
injected 600cc Motorcycle engine.  The header this is installed on will be a
testing-only header which also has EGT probes in it.  Purposes for
collecting exhaust pressure will be to design a custom camshaft that will
allow the engine to work with the restricted setup better.  It might also
contribute to advances in the design of our custom exhaust collectors.

Thanks in advance,
Craig Dotson
crdotson at vt.edu
2002 VT FormulaSAE

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