[Diy_efi] Pressure readings perpendicular to airflow

[Greg Hermann]

At 2:32 AM 6/3/03, Grant Beaty wrote:
>I've seem two books (Maximum Boost and one other) recommend testing for
>things like pressure drop, exhaust backpressure, etc. by just connecting the
>sensor to a barb that rests on the pipe. I've done this with intercooler
>pressure drop, and turbine inlet and outlet pressures.
>
>But doesn't bernoulli's law say that vacuum should be created in these
>circumstances? Wouldn't this effect the readings? Seems odd if it would,
>since this is how everyone does it AFAIK.
>
>I don't remember feeling any vacuum on the exhaust backpressure gauge when I
>routed it to the cabin and put my finger over it...
>
>Thanks for any help,
>Grant Beaty

A probe perpendicular to the flow measures "static" pressure. Yes, static
pressure goes lower as velocity goes up in an adiabatic flow.

A probe directed into the flow will measure 'total' pressure--which is
equal to dynamic (velocity) pressure plus static pressure.

A change in velocity converts part of the static pressure into dynamic
pressure or vice versa.

Greg



_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi