Re: O2 sensors AD #784

[bearbvd@domain.elided (Greg Hermann)]

>
>While there's nothing like the induction roar through a set of perfectly
>set up and balanced Weber carbs ( or Dell Orto or whatever your favourite
>happens to be) the fact of the matter is modern engine management computers
>can't be beat. That's why all the F1 teams use them, and yes Virginia
>that's an O2 sensor on that Ferrari V10 F1 engine.

BUT--that sensor on the Ferrari is a WIDE BAND O2 sensor. They do NOT tune
to the stoich a/f ratio on FI engines--because that is not the a/f ratio
which gives the maximum output. Some of the Aurora based Indy car engine
are now running a wide band O2 sensor on EACH cylinder--and by eliminating
the variation from cylinder to cylinder, they are are able to get best
power at an a/f ratio somewhat closer to stoich (but still on the rich
side) than they otherwise could.

A regular O2 sensor (such as what is provided on the newer Alfas) acts
pretty much like a switch at stoich a/f ratio. Tells you whether the engine
is above or below the stoich a/f ratio, and not much else.

And--by the way--these sensors switch at the stoich a/f ratio for whatever
fuel you happen to be feeding the motor: It you are burning a fuel whose
stoich ratio happens to be 13:1 rather than 14.7:1, then the 13:1 stoich
a/f ratio is where the sensor will switch when you run that fuel.

A wide band O2 sensor (working together with its control box) gives a
voltage output which varies, almost, but not quite, in a linear manner,
from 0 to 5 volts, as an engine's a/f ratio varies from 10 : 1 to 30 : 1.
The best, most responsive wide band A/F sensors/controls are made by
NTK/NGK. A wide band control box/sensor/wiring harness from NTK costs about
$1100 (USD).

You may find this rather incredible--BUT--a PROPERLY tuned set of Webers or
Del'Orto's will give BETTER (lower, more efficient) bsfc at wide open
throttle than all but the VERY most sophisticated design efi systems!

And I am not aware of ANY efi systems designed for street use which have
reached the level of sophistication necessary to match the level of WOT
bsfc that good, individual runner type carbs will give!

Not as much total power from the carbs as from efi, because the carbs need
the air flow restriction of their chokes to function,  but more work output
from the engine per unit of fuel burned at WOT with the good carbys, and by
a statistically significant amount (5 to 10%).

There are lots of complex technical and thermodynamic reasons for this
being true, but it IS a fact!

For the same group of reasons--it IS possible to obtain better throttle
response from properly tuned GOOD carbs than can be had from any normal
efi.

Regards, Greg

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