> Gasoline precipitation is only
> an issue at
> very low intake mixture velocities (idle) and this is why they added
> manifold heat (engine coolant passage) to the manifolds of later model
> cars.
FWIW, the earlier cars also have manifold heat ... it just isn't as well
controlled as the water-heated manifolds used on (some) later model cars.
On the early models, the intake manifold is bolted to the exhaust manifold
to provide the heat.
Also FWIW, there's a theory that a slightly rougher surface actually
improves air flow at WOT. It does this by creating a tiny boundary layer
that actually reduces resistance to the main airflow and reduces overall
turbulence. In effect, you get tiny little swirl cells near the size of the
roughness, instead of larger cells that extend further into the airstream.
This effect has been used to advantage on high-performance aircraft, and
even on golf balls.
But, the standard TR3/4 intake manifold features huge passages, and somewhat
unfortunate geometry. The TR4A manifold was the result of some addition
performance tuning, and addresses these problems with gentler curves and
smaller passages.
Randall
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