From: Wally Plumley [wplumley@bellsouth.net]
Sent: Saturday, December 30, 2000 12:03 AM
To: 928
Subject: [928] Re: Oh no, not another question!!! (not too long though)

At 10:30 PM 12/29/00, Jay Gary Wellwood wrote:
>Drove the girl home (~75 miles) with a noticable improvement in handling
>and ride.  I found a nice stretch about 10 miles out with few cars and
>decided to give her a 'test push'.  I am almost ashamed to report that
>~125 was the best I could do.  Seemed to have plenty of throttle available
>(i.e gas pedal movement and rpm reserve), just no increase in speed - and
>I was not going up hill either.


One of the symptoms of a partially plugged or restricted exhaust system is 
limited top end. The car will run well, and have no apparent problem, but 
will just not go fast.

The easiest test is to hook up a vacuum gauge to an intake manifold tap 
(not the venturi vacuum, nor after a check valve). Crank the engine - there 
should be perhaps 16" at idle. Pop the throttle open enough to hold the 
engine at a steady 2000 rpm. The vacuum reading should drop as the throttle 
is opened, then jump to a fairly high and steady reading, perhaps 20 - 22". 
Hold the engine speed (not the throttle opening) steady for thirty seconds. 
The manifold vacuum should hold steady at the high level.

If the exhaust is partially plugged, there will be a steady drop in 
manifold vacuum, and if the restriction is bad enough, you can end up with 
full throttle and zero vacuum at 2000 rpm.

Wally Plumley
928 Specialists