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
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
Years ago I got a Solar turbine sticker that said" Do not exceed
100,000 RPM and put it on the dash of my RX3. Messed people's heads
up. Tension breaker; had to be done.
Dale Davies
Dale, Good catch! I was missing the decimal point there, but as I
messed up twice in my last post, I'm hard just to train.
And I do Love the RPMs though, especially after I stepped out of my
'72 T/A 455 HD into a '73 RX7 in 1979. I've never looked back
Regards, Ray Hellstrom
You had a 73 Trans Am? I did the spoilers on that for Pontiac. I am
still in touch with Herb Adams.
Paul Lamar
I didn't know that at the time but I learn this year's ago when I first
found your rotary web site. Amazing stuff.
Oh BTW, I just read another thread you have going where you give the
length of runners and max. HP & torque /rpm. My 13b puts out 160.61 HP@
7.4K rpm & 126.7 ft/pds @ 6K using a Weber 48 IDA running 37mm choke on
top of RB manifold, with a total length of ~12" long.
I know this is low but I am running in NASA Time Trials so any
improvements to the car as well as power to weight ratio determine which
class I run. I need to look how I prepare for next year's season because
at this time if I go for more power, I'll be pushed up into the class
where the supercharged and turbocharged Miatas run.
Anyway just wanted to share the results from the dyno run.
Regards,
Ray Hellstrom
We have been at it for 18 years :-)
That is about right for a side port.
Are you allowed p-ports?
If so 300 HP is available at about 9.500 RPM or maybe 10,000 RPM.
This happened almost 30 years ago :-)
I think they are now making 51 or 52 MM Weber or Chinese copy Weber carbs.
There is a u-tube video on this. We made 250 HP on the dyno
with an RX8 p-port and Weber at 7500 RPM. Side exhaust no less.
Search U-tube for "PaulLamar2"
If NASA allowed a turbo 2 rotor 650 HP would be available. Do they have
a class for that? :-)
Paul Lamar
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