Back-pressure Measurement Techniques?

[Wicsteve]

Many small engine manufacturers use exhaust backpressure specifications for emission conformance guidelines. Such specifications are often given to a muffler manufacturer for use in designing an exhaust system.

There does not, however, appear to be any consistancy between engine manufacturers (or suppliers of mufflers) as to the procedure used for measuring back pressure. We've seen measurements made in the first chamber of the muffler, in manifolds at locations immedately downstream of the exhaust ports, in the bends of exhaust manifolds, with different probes, in mid stream, at the tube walls, etc. We've seen drastic differences in measured backpressure depending upon small changes in location of the measurement. In twin cylinder engines there can be large differences in back pressure readings between cylinders (with similar manifolds).

This presents the question for general discussion. Can the forum share some good techniques for taking back pressure measurements? Are there accepted practices and advice for making pressure measurements in manifolds? Since measurement technique appears to affect the results so dramatically, can there be any validity in back pressure specifications for assuring that an engine conforms to emission standards?

 

[carnage1]

The omega looks perfect but I would still suggest the $20 for the motorolla unit to make sure that there are not any waves of great enough magnatude to damage the omron unit. It seems like cheep insurance to me.

 

[carnage1]

That last post was supposed to read Omega both times. We use omega for temature and pressure controls and omron for timers.