When I dyno a car I always use one of my widebands placed in front of any
cats and the dyno facility uses a
wideband tailpipe sniffer. In the case of cat equipped cars I see a
consistent offset 0f 1/2 of a point in single
cat systems and .7-.75 of a point in cars with two cats per bank.On
carbureted cars I see only a couple of tenths
difference between my sensor(usually placed in a collector or just past
the collector) and the tailpipe sniffer.
Any well designed exhaust system should have only a couple of pounds of
back pressure so those effects should be
negligible.
Ron
p.s.
Randall, you're one of the reasons I don't post much. By the time I can
come up with a response you've
already responded with a great response.
On Tue, 20 Apr 2004 19:09:21 -0700 "Randall Young"
<ryoung@navcomtech.com> writes:
> > I have two widebands and I tune a lot of turbo'd and supercharged
> cars
> > and they are indispensable.
>
> For situations like that, where the fuel curve has to be altered, I
> agree
> that a wideband O2 sensor would be a great help.
>
> > I only have two Triumph customers and one of them was quite happy
> with
> > with his own tune on his carbs,
> > I finally persuaded him to let me use my wideband and he could see
> for
> > himself how far off his wot a/f ratio was.
> > His a/f was between 17:1 and 18:1 and he thought the car ran just
> fine,
> > we did a lot of tuning and brought that down
> > to about 12.5:1 and he went from 115 SAE hp to 142 hp at the
> wheels.
>
> But note that even a narrowband O2 sensor would have gotten him much
> more
> power ... at least on the rich side of 14.7 to one instead of way
> out on the
> lean side.
>
> > Anyway, I feel some of you more serious racers could benefit from
> this
> > technology.
>
> It's on my wish list !
>
> BTW, Ron's chart didn't make it out to the list (which blocks all
> attachments including all forms of graphics). He sent me a nice
> chart
> purporting to show the response curve of a narrowband O2 sensor,
> with the
> entire range of response located between 14:1 AFR and 15:1 AFR.
> However, it
> didn't include the effects of exhaust backpressure and sensor
> temperature,
> both of which I understand distort the curve substantially.
>
> Randall
|