Esteemed List Memebers,
Consider for amoment how much air a Spitfire needs:
1500 cc =~ 91 Cu in
7500 RPM = 3750 intake strokes/min
91 * 3750 = 341,000 cu in/min
1 cu ft = 1730 cu in ( 12 * 12 * 12)
341,000 / 1730 = 197 cu ft/min
This is at 100% Volumetric Efficiency.
(your chances of reaching 100% VE with a Spitfire are
slim)
The CFM ratings of carbs (and throttle bodies) are
measured at a specified pressure drop, I believe it is
about 1" of water (not much). So in term of raw flow,
anything more gives very small performance gains.
What is critical to good running with a carb is the
mixture control that can be maintained over a wide
range. This is not simply the air/fuel ratio, but also
atomization, uniformity of the mixture, and response
to transient conditions (like sudden WOT) and
different environmental conditions like temperature,
relative humidity, air density (altitude).
The advantages (and shortcomings) of all the carbs
listed can be attributed to how well (or poorly) these
issues are handled.
A well tuned and fitted ZS could outperform a badly
tuned and fitted Weber on the same engine. But the
Weber can be tuned to within a gnat's whisker of
perfect (in the hands of the right person). While a
ZS, well ........?
Modern computerized engine management can achive this
feat reliably and repeatably. This is one reason that
current engines achieve such astounding performance.
( 100 HP/L *and* 35 MPG, meeting emission control
regs, docile and tractable under all driving
conditions)
But I think my Spitfire is a lot more fun to drive!
Carter
--- "Terry L. Thompson" <tlt@digex.net> wrote:
> The cost is reflective of the performance as well.
>
> A single Zenith Stromberg (150CD or ? cfm) can be
> had rebuilt for as low as
> $100-$200.
>
> Dual SU HS2 (1.25" or 90 cfm per carb) set-up can
> cost anywhere from
> $150-$350.
>
> Dual SU HS4 (1.5" or 142 cfm per carb) will cost
> around $200-$400.
>
> Dual SU HS6 (1.75" or 210 cfm per carb) will cost
> around $300-$600.
>
> Weber 32/36 DGV (255 cfm) will cost around
> $400-$500.
>
> Weber 45 DCOE (400 cfm (32 mm choke), 420 cfm (34mm
> choke), 440 cfm (36 mm
> choke)) I have no clue how much $$$.
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