In a message dated 97-10-28 12:41:27 EST, curry@wolfenet.com writes:
> The real reason for
> damping (as is evident in the definition of the term) is to make the
> engine run smoother by eliminating oscillation of the piston.
>
> Without the oil, it would have a tendency to jump to the top on
> acceleration un-impeded and be forced down by the spring as soon as the
> vacuum drops. The oil slows the ascent of the piston and makes it less
> sensitive to erratic changes in vacuum.
I'm not trying to irritate you, Joe, but I must comment on those statements.
The real purpose of the damper is to supply an extra "squirt' of gasoline to
the engine during sudden acceleration. This is the Brit's way of doing the
same thing the accelerator pump does with American carburetors. Any dampening
of "erratic" changes in vacuum is just a side benefit, if any benefit at all.
< Since In racing The foot is on the floor all the time (well most of the
< time),
This statement is the key to the benefits of no oil in a racing engine
carburetor. The only time (for the most part) the foot is off the accelerator
pedal is during gear changes, and since the dashpot has no dampening effect
on the downward motion of the dashpot, the piston would instantly drop during
that momentary throttle off condition. During that time, the engine has
insufficient time for a significant change in RPM, whether upshifting or
downshifting, so the air flow through the carburetor is roughly the same
before and after the gear change. Because air flow under these conditions is
sufficient to create a strong vacuum signal to the jets, the extra squirt of
fuel is not needed. If the dashpot were dampened, there would be a time delay
to full throttle position again, at a time when it is not needed, and
certainly not wanted.
Even when braking for a corner without a downshift, the engine RPM is not
allowed to drop enough to need the dampening effect of the oil. If the corner
is slow enough to cause a large drop in RPM, there will be a downshift
involved, which will bring the rpm up again.
Barry Schwartz, jump in here please! Correct me if I'm wrong!
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
|