Sherman :
As in most areas of automotive engineering, there are compromises and
tradeoffs here, that inter-relate.
There is a 'perfect' air-fuel ratio (stoichiometric sp?) around 14.7:1
where the amount of oxygen exactly matches the amount of fuel to be
burned. Car engines produce the best fuel economy at (or just slightly
lean of) this point. However, for a variety of reasons, they make the
most power at a somewhat richer mixture. The richer mixture also helps
suppress knock, and lower exhaust gas temperatures (and increase
pollution <g>).
So, for a street engine (where fuel economy is important), you want the
cruise mixture to be around 14.7:1, while the 'full throttle' mixture is
around 12 or 13 to 1. The SU and ZS carbs implement this with the taper
in the needles. However, for best throttle response, you also want the
mixture to go rich immediately when the throttle is opened. This is
(one of) the effects of the damper. However, the damper also introduces
a certain amount of resistance to air flow, which (briefly) limits
power.
So, on a full race engine, where fuel economy is less important, the
carbs are usually setup to provide the maximum power mixture (or close
to it) all the time. (This, in addition to similar modifications, is
presumably the reason that "Uncle Jack's" TR4 only gets 10 mpg <g>)
Now, the damper only represents a power loss (and possibly would take
the mixture too rich, which is also a bad thing), so it is left empty.
Of course, again like most areas of auto engineering, there are
differing viewpoints. I'm sure we'll hear some opposing ones <g>
Randall
"Taffel, Sherman" wrote:
>
> I also remember that the race tuned TR-4's specified NO OIL in the
> dashpots.
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