I do have a question concerning where I should be taking my AFR
readings on my 13b powered RX7. I have one sensor installed on the
header about 8" from the engine and as I accelerate I see readings
going from 14:1 at 3K RPM and going to 10:1 at 75K RPM as I am on
track.

Two weeks ago I ran the car on a dyno after my second session of the
day and that showed that in fact, the AFR reading at the top end is
actually just going lean at 75K RPM. So, is it better to install the
sensor back at the rear of the exhaust, just down stream of the
collector and before the muffler?  Thanks for your input. Love
reading the emails.

Regards,  Ray Hellstrom

Check the fuel pump volume Ray. Sounds like the fuel pump is running
out of grunt.

Paul Lamar


Paul,
My fuel pressure stays at up around 6 psi and I don't see it dropping at
any time.
I am questioning where to read the AFR. During the runs on the dyno I
saw the Innovate AFR meter in the car topping out at 10:1 at 7.5K RPM
while the AFR sensor on the dyno was starting go lean. Is it just the
distance and mixture of both front and rear rotors.
Regards,
Ray Hellstrom


My mistake. I assumed you had fuel injection.

My Motec people say it does not matter where  the O2 sensor  is.

Do you have a wide band ?

Paul Lamar

Hi Ray,

I have a AFR gage on a small Rotec radial. Remember it is an Air/Fuel gage, and we are looking for ideal stoich ratio of 14.6.

Those figures indicate that at 3K rpm you are running slightly rich and at 75K, you are running very rich.

If the engine is making good power, I doubt there is anything wrong with the fuel delivery system.

What brand AFR are you using?

Dave Mccandless in Oz

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