STU-TO writes:
>Barry, I hate to disagree with someone offering advice, but the TR8 manual
>gives a spec of 9-16 degrees advance at 12" of vacuum, then in a separate
>table gives 10-14 degrees of retard at 12" of vacuum. Since the distributor
>has both vacuum advance and retard, the retard line comes off the manifold,
>and .the advance comes off the carb. As I rev the engine I can stick my
>finger over the advance hose and feel it sucking stronger. The mechanical
>advance is only 22 degrees at 3000RPM, hence my concern. StuTU
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You can disagree all you want :-), that's your prerogative. The fact
remains every thing I said was true. No flames here - Your running your
'test' at static, no-load conditions. It's impossible to get a wide open,
full throttle condition and not grenade the engine without placing a load
on it. If you really want to see actual road, real world conditions, then
put a vacuum gauge on your engine while you drive it. You will see exactly
what conditions exist during normal operation. I have had these installed
on several cars over the years, in fact one on an AMC that I was tuning a 4
bbl Holley carb on so that I could see what the vacuum reading was to fine
tune the power valve operation point (also known as the economy valve).
You can realistically expect to see a no vacuum condition if you mash the
throttle at 1000 or 2000 rpm until you get to your cruising speed and back
off the throttle, creating a restriction in the manifold. This is what
causes your 'vacuum'. The engine is still trying to pull the full amount
of air that the volume of the piston/stroke and valve opening will allow.
Your throttle plate, partially closed is preventing this. This difference
in the pressure inside the manifold from atmospheric is what we are calling
vacuum. It's interesting to note also that on some *very* early cars the
wipers were "vacuum" operated and on very long steep hills, they would stop
working - because there was no vacuum under these full load conditions. I
personally have never driven such a car, not quite old enough <G>. . .but
have heard stories. .:-) It's also worth noting that many diesel engines
employ a vacuum pump to operate devices that require vacuum because there
is NO throttle plate and simply meter the required amount of fuel depending
on the load conditions. Typically at cruise you will see anywhere from
15-20 inches. A lot depends on the cars weight/gearing/horsepower.
Barry Schwartz in San Diego, CA
Bschwartz@encad.com
72-V6/5sp Spitfire ( daily driver )
70 GT6+ ( when I don't drive the Spitfire )
70 (sorta) Spitfire ( project )
73 Ford Courier ( parts hauler )
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