Re: Exhaust Back-Pressure, ever check it?

["Graydon D. Stuckey" <graydon@apollo.gmi.edu>]

On Sun, 30 Nov 1997, Scott M. wrote:

> pressure after the turbo (exhaust back pressure) was
> measured to be 0.5 psi. 

With a good free flowing exhaust system, this is about what I'd expect.

> Has anyone with a '86-90 5000/200TQ that are currently
> running 1.8-2.0 bar ever check their exhaust system back
> pressure while under full boost? I did this on my 89 200TQ

Not yet.

> using the pre-catalytic converter sniffer pipe that
> connects to the exhaust pipe at the turbo exit. This metal
> tube is bolted to the intake manifold and is typically used
> for adjusting the CO% using an exhaust analyzer. I did not
> like what I saw on the pressure gauge while in 3rd gear,
> 1.8bar boost at WOT ~6000RPM.............take a guess how
> much pressure was shown on the gauge.....1 psi? 2 psi? 4
> psi? 6psi ? 8psi? 10psi?

If you have a stock exhaust, I'll guess a couple psi.

> Is there any reason why this location is not a good place
> to measure the exhaust back pressure?

I can't think of any.   If we were measuring vacuum, I'd be concerned 
about venturi effect, but we're measuring pressure, so iti should be 
accurate.

> > It would be interesting to see the difference in exhaust
> back pressure on those cars that have the stock turbo but
> are running the 3.0 inch exhaust system. If you show me
> yours, I'll show you mine............

I'll check it out when I get my car back on the road.   Might be next week.

Later,
Graydon D. Stuckey 
the "Muffler Man" this week