On Fri, 15 Aug 1997 18:16:39 -0700 Sergio Dimarmo <wanderer(at)sure.net>
writes:
>My old 65' Triumph TR4 had dual 175CD's on it similar setup to the
>Alpine. My friend had a Series V at the time and the only difference I
>saw between the 150 and 175 is that the 175 is a little taller.
>Although
>we did not measure it the bolt pattern seemed to match. Wouldn't these
>be too much carb for a stock Alpine?
>
>Serg
The term too much is subjective.
A stock alpine motor will readily accept twin sidedraught webers, and
will
make another 10 BHP doing so.
On variable venturi carbs like CD and SUs, the size of the throttle plate
is not the limiting restriction.
"unless it is smaller than the wide open area of the venturi."
What is the limiter is the spring loaded venturi piston, which is
lifted by the depression sensed between the throttle and the
back side of the venturi piston.
The depression lifts against the weight of the piston, as well as the
spring.
In this way the depression there is held constant CD=constant depression,
and the cross-sectional area of the venturi changes as a function of the
volume airflow.
Now, all that aside, if the 175 has an appropriately larger piston size,
and about the same size diaphragm, the depression level will
be about the same as that of a 150, but at a corresponding higher flow.
This means that the restriction as a function of flow will be lower (CV),
and that the larger throttle plate, will make the pedal more sensative,
and add a little more top end power.
If you have them (175s) and they fit, I'd use them.
I doubt you'd notice any major power increases though.
The 150 carbs are well suited for the displacement of the 1725 motor.
Jarrid Gross
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