---- Stuart MacMillan <stuartmacm@gmail.com> wrote:
> Right, but by that logic the funnel should have been used on all vehicles to be equal conditions since it caused some degree of backpressure.  I'm sure many more would not pass in those days if they did.

That might be correct.  I assume the funnel is to direct the exhaust into the test device.  Without it on some vehicles, some of the exhaust would escape.  Test devices in this day and age are usually idiot proof, being set so that an operator only enters a set of values, operates the device, and gets out a result.  The operator may not even know anything about the operation except to enter the specified values and to read the result (for example as "pass" or "fail").  Is the vehicle type, make, model, and year among the values the operator enters?  If so, the device is likely calibrated for test conditions for each vehicle type.

But what do I know?

Interesting discussion.  mcneely
>
> Stuart
>
> > most important, is that he was able to talk the tester out of using
> >the  funnel they were supposed to stick on the wand for short tailpipes
> >like the  Vanagon's.  I think that had the most to do with it because
> >without it there  was more air dilution of the exhaust gasses.  That
> >stupid funnel kept the  gasses in the tailpipe longer, and I didn't
> >think it was fair.  They didn't  listen to me though.
>
> Well, the test conditions are set to be constant for all vehicles.  One is not testing against the ideal, but against the conditions of the test.  If what is supposed to be a constant is varied, then the result will not yield the desired information -- whether the vehicle is operating properly as required.  mcneely
>
>
>

--
David McNeely