I don't know if anyone has answered this or not since I still
have 372 messages to read !!.
On a four cylender engine, only one cylender is drawing in air
at a time (180 degrees of rotaion, just for argument sake, not actual
cam specs). So basically, the carb is just right for ONE cylender. So
a single CD-150 will make the engine run fine, since it only has to
suplly the cylender one at a time. Going to twin CD-150's shortens and
straitens the path the misture must take before entering the cylender,
thus making a bit more effiecient. If there was room you "could" go to
four CD, however, they do require a fair amount of vacuum to lift and
maintain the slide. So have only one intake suck pulse every two
rotations typically don't work well in (basically) low RPM engines with
constant velocity carbs like the CD-150, or SU's. Twin side draft
webbers, which are really four carbs with two shared float bowls, are a
better choice, and will typically produce the most horse power.
This changes on a V-8 engine because there is some significant
overlap in the intake strokes of these engines, so the carb has to be
able to supply 1.5 to 1.75 cylenders at once. On an unmodified engine,
you would normally drop a size or two if going to dual carbs, depending
on the intake manifold design. The old Six Pak (3 two barrel carbs)
usually used failry small carbs. Does this make sense? I'm pretty
tired.
Rich
> ----------
> From: Sergio Dimarmo[SMTP:wanderer(at)sure.net]
> Reply To: Sergio Dimarmo
> Sent: Sunday, August 17, 1997 7:48 PM
> To: Lauri Lehtinen
> Cc: alpines(at)autox.team.net
> Subject: Re: CD 150's - There's gotta be something better out
> there
>
> Lauri Lehtinen wrote:
> >
> > Serg Dimario wrote:
> >
> > >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
> >
> > I quess yes. If factory have calculated 150 is enough, then it is.
> Engine
> > can swallow only known amount of mixture, and bigger carb gives it
> with let
> > us say 7/8 throttle. That final 1/8 is useless.
> >
> > Funny thing, if you replace single carb with two, you must use same
> > diameter throttles? At least with brit twin bikes.
> >
> > Lauri
>
> Now I don't understand that.......why wouldn't you split the diameter
> between the two new carbs? I don't get it....of course, I'm not a
> physics major, I'm not even a private.
>
> Serg
>
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