Dan Buettner wrote:
>
> >But the 2 1.25" SU's with their combined 2.12" area is still better
> >than the single 1.5 ZS with 1.766", right?
> >
> >Joe
>
> Yes - and no. Depends on the size of the engine, among other things.
> Carbs have to be sized appropriately to the motor.
>
> If one were to put a pair of really stinkin' big SUs on a Spitfire
> motor, I would imagine that it wouldn't run well at all. The air
> velocity going through the carb body might not be sufficient to draw
> enough fuel up out of the jet, and atomization might suffer as well.
>
> On the other hand, carbs that are too small will effectively cut the
> engine's breathing ability, as air simply can't travel into the
> cylinders fast enough.
>
> All that being said - yes, I would venture to say that two 1-1/4" SUs
> are better for a 1500 than a single 1-1/2" Stromberg. From
> everything I've heard, two 1-1/2" SUs are even better for the 1500s
> ... the same might not be true for the 1147cc and 1296cc motors,
> though!
The question wasn't whether 2 1-1/4" SU's would work but rather would they
deliver more air/fuel than a single 1.5 ZS. And because of the increased
choke area, that would definitely be true without question.
The question of whether or not it would beliver greater performance than a 1.5
ZS, based on personal experience they certainly do. Of course, this
assumes that the engine is otherwise in good operating condition. A poor motor
will still be a poor motor regardless of what sort of carburetors are
installed!! :)
1.5" SU's might work better for European 1500's but unless modifications are
made to the US version 1500, it might not perform any better with 1.5"
SU's than it would with 1-1/4" ones. The European engines were not hamstrung
by all the emission controls that the US engines were.
Joe
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