Just for edification: I had stacks!!!
Geoff Branch
'74 Meejit "Yellow Peril"
'72 Innocenti 1300 Mini
----- Original Message -----
From "Robert E. Shlafer" <PilotRob at webtv.net>
To: <Daniel1312@aol.com>
Cc: <gjbranch@attbi.com>; <spridgets@autox.team.net>
Sent: Wednesday, June 25, 2003 6:48 PM
Subject: Re: SU question
> 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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