Daniel1312@aol.com wrote:
> What Scott says about venturis is true. However, a 45DCOE with 34mm venturis
> is probably making less brake horse power AND making less torque than a single
> 1.75 HIF6 carb - or so some well respected experts advise me. The reason for
> the big SU working so well is that has the advantage of being a variable
> venturi carb, whereas the DCOE is a fixed venturi carb albeit one that can
> have the venturi changed from one size to another.
Aha! I had forgotten about the variable venturi effect. Very good point.
I wonder if the dual smaller SU's would improve on the torque - say 2 slightly
improved 1.5" SU's? Or would the 1.25's be best for torque and power below
6000rpm?
In Autocross (i.e., SCCA Solo II) most of the courses are second gear, with
occasional (brief) third gear moments. Rarely is there the need to shift back to
first. The average course is in the 45 to 75 second range. There is a lot of
time
spent between 3000 rpm to 5500rpm, *BUT*, with the occasional need to handle a
180' turn.
Since I refuse to try to shift to first in my Sprite, torque at 1500 to 2000rpm
is of significance.
FYI - Often is is not advantageous to downshift into first for a 180' turn
anyway, because of the wheel spin typically produced.
> BUT,returning to my question of is the SU better than the DCOE, the only thing
> I am not so sure about is whether top end BHP aside (where the DCOE is
> superior) does the Weber DCOE whether or not 'choked down' with small venturi,
> gain over any SU setup by virtue of the acceleration pump jet system. In
> other words when the pedal hits the metal does a Weber DCOE carbed engined rev
> quicker (not revs more) than the SU? I suspect it does and that this is why
> there is more to performance carburation than dyno and flowbench figures
> suggest?
As with turbo-engined cars in Autocross, one can anticipate "throttle-on" and
avoid any throttle hesitation by slightly early application.
I am very intersted in this discussion, because my effort is to create a
successful Sprite in (USA) SCCA Solo II competiton in D Street Prepared. Right
now the current "King of the Hill" is the Fiat X1/9. The Sprite is current
champion in D Prepared, where they must run SU carburetors, but cams, engine
and
suspension modifications are quite open.
> PS. Is this the Scott that made the cover of Tom Colby's newsletter a few
> years back?
Nope - the Scott from Phoenix Arizona, working on his 5th Sprite (although my
first in many years).
Anyone with experience please add to this discussion - what would (have?) you
run
for carburetion, given the parameters above (best power and torque within
2500-5500rpm)?
Thanks,
Scott Meyers
60 Bugeye
Engine out - installing a stock cam (required by the rules),
removing the Isky 320' cam the PO had in there :-(
a REALLY bad choice for a cam for ANY purpose......
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