You know....
I could not agree more on this...even a
decent stub-stack would be of help and
yet.....people just don't "get it" for reasons
I do not know. And Vizard makes a point
of explaining all this.
As do Passini's books.
While a good filter in and of itself will
help smooth out airflow, you cannot beat
a combination of both filter and stub stack
and/or air horn. Especially for low end
street torque in consideration of your remark on "fixed venturi (choke)"
design,
Daniel, at least in accordance with my
experience. Especially in view of the fact
the Weber has bigger "holes", as well.
I have never run my 45 without airhorns
(at least short ones if nothing else) along with the deepest (K&N in
this specific case) air filter I can get in there, even
cutting the inner fender and rain gutter
on the left side of my PO'd '74 to fit
it all in there with a 6 inch intake manifold.
There is another thing also, and that is
inlet manifold length. Here again, Vizard
explains it all and yet, I am sure there are
those running around with "short" intake
manifolds complaining about poor low
end street performance of the "DCOE carburettor", when in fact the
length of
intake manifold is unsuitable for the
application. And millimeter for millimeter,
longer velocity stacks on the "other end"
won't fully make up for "shortness" at the
"other end", though they will help in this
respect.
According to Vizard the stock SU intake
manifold is the main culprit blocking
better flow to the head in terms of the
stock 1.25x2 set-up (not the fault of the
carburetter), just a change to an intake
manifold delivering a far more unemcumbered "straighter shot" should, in
and of itself, make a major difference in
performance and response. But without
smooth airflow at the carbs. mouth, you
may not see this if going over to the
larger "holes" of a 45 DCOE.
Matter of fact, with the "holes" being
"larger" and the carb. now being of fixed
venturi rather than "variable venturi" low end torque would certainly be
much worse than with the stock SU set-up with it's
smaller holes, without "flowing" intake
air at the carb. mouth(s) with air horns
or stub stacks.
I mean I can remember being unable to
set the idle properly in the stock 1275
which came in my PO'd '74 Midget due to
some air leakage by the throttle shafts.
Nothing major mind you. Off idle the engine ran just fine but the idle
was uneven and there was excessive back-
firing out the exhaust on over-run and
deceleration in gear. So I said, what the
hell, we'll convert to a "45" rather than
rebuilding the stock SU's.
After sticking in the correctly calilbrated
Weber Kit for the stock 1275 and trading
back the longer velocity stacks for the "shorties" (the kit came with
the Weber
6" manifold already as a street application
so no need for "longer"...just something
to "smooth" airflow). Set up the idle mixture according to the book,
turned
the key and drove away.
The kit came with velocity stacks. They
must have been included for a reason.
This WAS the official Weber Kit, after
all.
Worked absolutely fine. No performance
or gas economy problems at all. Low end,
mid-range, top end...all worked just fine.
Never had a bit of a problem with it.
"Response" has always been more quick
than the SU's and fuel economy has always been fine in 3 Series A
configurations I ran with the "45" from
plain stock, to mildly tuned, to about as
tuned as it can get for the road with big
valves, etc., while retaining a decent low
range for street driving. I started with
34mm chokes, went to 36 and finally ended up with 38's for the latter
(Vizardized) 1380 motor (7000+ "redline).
I will say that with the latter 11.0-1 Vizardized 1380 "might mite"
motor
with it's 1.414 intake valves (Rimflows)
"big bore" header/LCB through a 2"
exhaust and Cherry Bomb glasspack,
that off the line from idle rpm, the car
was "quicker" at 1/2 to 3/4 throttle than
WOT, initially. "Flooring it" instead would
not produce a bog, but initial torque was
better under 3k if you did NOT floor it.
Revving the motor to 3,000k before dropping the clutch was a different
matter
in this respect of course (hardly ever did
this)...then, WOT all the way!
Considering all the above, I accepted this
as quite normal for a car that was about
as hot as you get for the road and still
retain "reasonable" traffic manners. It
wasn't "happy" in heavy traffic but it
was not "unuseable" in such conditions
either, even when outside air temps. got
to 90F.
A lot of carburettor faults (as in the case
of DCOE's) are not carb faults. The same
goes for other fixed ventui set-ups, most
especially their twin throat "progressive"
downdrafts WITHOUT water heated intake manifolds.
And...there is also nothing wrong with a
mechanically sound set of SU's...this is
NO intended as an argumentative "for" or "against" kinda post. :):)
'Course, you're probably asleep by this
time, anyway...it is sorta long...sorry!
Cap'n. Bob
'60 :{)
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