Dave Rupert wrote:
> Isn't it the other way around? The oil is supposed to
> work as a damper, so getting rid of it would make the
> piston move more quickly.
That's right, but there's more to consider...
The piston controls how much air gets in to the engine.
The intent with the piston travel being damped is to slow
the piston down when rising, so that less air gets in the
air/fuel mix -- resulting in a richer mixture. When
accelerating, if the car was tuned for emissions (somewhat
lean), suddenly opening the throttle will cause the
air/fuel mixture to be under-lean, giving lousy performance,
and maybe pinging as well. Typically, a richer fuel mixture
is desired for acceleration.
For the factory-tuned car, it is better for performance
to let a little less air in but with a richer mixture (as
caused with the dashpot oil) than it is to let lots of air
in, but with an overlean mixture (as with dry dashpots).
That said, I have a '74 TR6 which is mis-tuned to run
quite rich. On this car, the mixture is always rich,
so it really isn't necessary to have an even richer
mixture on acceleration -- the standard mixture is
already rich enough. Thus, for this mis-tuned car, it
doesn't matter whether or not there is any oil in the
carb damper, since even when the throttle is suddenly
depressed, the then-leaned out mixture (since no oil in
dampers) is still rich enough to give good acceleration.
If the mixture is far enough off (on the rich side) to
give reduced performance due to an over-rich mixture, then
having no oil in the pistons will actually *increase*
performance, as it will lean the mixture out to where there
is more power.
My speculation with the cars in question is that the
cars were mis-tuned to be over-rich (like my '74), so
that sudden throttle depression doesn't result in an
under-lean mixture, because the mixture was too rich to
start with! If anything, the mixture may just get leaned
out to where it belonged in the first place...
In the long run, I think you'll do as well by leaning out
the mixture in the carbs to maybe just a little richer than
specified by the factory, and then relying on the piston-damper
oil to enrich the mixture under acceleration. If nothing
else, you'll be a lot happier on fuel consumption, as well
as "greener."
(My '70 TR6 is tuned slightly lean, and gets 27MPG;
my '74 TR6 is tuned quite rich, and gets about 17MPG.)
--ken
'70 & '74 TR6 Daily Drivers
--
Kenneth B. Streeter | EMAIL: streeter@sanders.com
Sanders, PTP2-A001 |
PO Box 868 | Voice: (603) 885-9604
Nashua, NH 03061 | Fax: (603) 885-0631
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