Typical A/F ratios:
high 14's up to "0 PSI" AKA
atmospheric pressure (1 BAR)
mid 12's up to 6 PSI (1.4 - 1.5
mid 11's up to 14.5 PSI (2 BAR)
Fuel related links:
Detailed information on both
In terms of ignition, proper timing is needed to ignite the
compressed air/fuel mixture at the most opportune time avoiding preigniting
(detonation) or retarded ignition
Typical timing advances:
30 to 35 deg advance to 90kpa
20 odd up to 120kpa (1.2 BAR, 3
as low as 10 to 17 total advance
up to 200kpa (2 BAR, 14.7 PSI)
If you stick
to a total engine advance of no more than 15 deg, assuming your static timing
(pick up) is set correctly, then you are much less likely to suffer engine
failures due to timing
Exhaust gas temperatures is one way to measure
timing. If the timing is too retarded (combustion happens too late) then
the fuel is still burning in the manifold causing higher EGTs
Effects of porting on timing:
*1 BAR boost assuming
constant ambient temp of 15 C and charge temp of 30 C*
20-23 deg advance ...lowest effective "dynamic" compression at max power.
15-17 deg advance...midrange effective "dynamic" compression at max power.
10-12 deg advance...highest effective "dynamic" compression at max power.
Before you tune you must ask yourself:
1) What ECU are you using?
2) What amount of performance/reliability do you want from your car?.
3) How modified is your car?
4) How much boost do you plan on running?
5) What octane gas do you use? (better be more than 92 octane)
6) How easy is it to access a dyno, wideband O2 sensor and data logging kits for
all vital engine information?
7) Where is your EGT sender located?
Wide Band O2 Sensors
Why do I need a wide band 5-wire sensor on my air fuel
1) The output of a sensor with less than 5-wires is binary. That means
it'll only tell you if you are rich or lean. It cannot tell you how rich or
lean you are. Once the mixture goes a little bit fat, the meter will pin to
the rich side. Likewise if the meter goes lean, the meter will pin to the lean
side. Very often, a meter maker using these cheap sensors will write on their
faceplates that the meter goes from 10.0 to 20.0 AFR. This is just paint on the
panel. It is simple dishonesty. It is more likely 13.5 to 15.0 in reality.
They might as well use three LED's to tell you the AFR - LOW, MED and HIGH!
2) There are only two wide band sensors widely available today. One is
made by Bosch and the other by NTK/NGK. They have five wires. These sensors
require sophisticated closed loop controllers to determine the air fuel ratio
rather than a simple switch type OEM sensor that requires only a voltmeter. All
sensors can only determine the air fuel ratio at the switch point where the
mixture goes lean to rich. This is any sensor's zone of accuracy. The
difference between the OEM sensors and the 5-wire widebands is that this zone
can be moved around to different air fuel ratios in the widebands. In other
words, 5-wire sensors have an electronically controllable air fuel ratio in
their reaction cavities.
What this means is that you can make the sensor operate in it's zone of
sensitivity at air fuel ratios ranging from 8 to 24 or higher air fuel ratio.
The problem is that this requires some clever circuitry to keep the sensor in
this delicate balance. (lamdaboy)
Many RX-7 tuners actually wire their wideband directly into the O2 sensor
location for the aftermarket ECU. As long as the Wideband O2 sensor has a
1-4V output it can replace the stock O2 Sensor. Many do this so that, like
in the PowerFC, one unit logs O2 and all other engine parameters.
The standard scale is: 4V is amount of oxygen in open air
2.5V is combusted fuel at a 14.7 A/F ratio
This is the
Tech Edge Wideband O2 sensor kit
which is used in proper tuning of a RX-7
This is the
FJO Wideband O2 sensor kit
which is used as well.
Standard Air Fuel Ratio Meter
LM-1: Digital Air/Fuel Ratio Meter
Data Logging ability with excellent software
All of these kits have a data logging feature which is crucial for tuning
because it retains past information so tuning does not have to be "on the spot"
Data is logged into either a laptop or a PDA and reviewed as the fuel map is
corrected to get as close as possible to the desired Air to Fuel Ratio.
Stoichiometric combustion is always dreamed about, but is unattainable due to
the detonation in turbocharged rotary engines. Detonation is more likely
with the air is hot and pressurized. It is a debate as to what the
"correct" AF ratio is for a FD. I have personally seen as low as 11.5 to
as high as 13 used in setups. (this information is used as education
This website chronicles an installation of a wide band o2 sensor on a 3rd Gen
Use primarily in tuning the ignition maps for the RX-7, the J&S Knock Sensor
is not only a monitor, but a safety net as well. The unit is capable of
detecting preignition and displaying that to the driver. The unit adjusts
timing as needed to avoid early timing. If the timing is too soon
preignition/detonation will occur. If the timing is too late, the timing
is considered retarded and ignites what is already expanding because the rotor
is in motion causing a change in pressure and volume. Perfect timing is
This document has several articles related to knock sensors and detonation.
Datalogit for PowerFC
Data logging unit that "splices" the signal for the commander and sends it to
a laptop via serial port. The laptop must have correct software installed
to read signals and log data from ECU. Most useful features include
logging Load vs. RPM graphs and correction maps.
The manual (PDF)
This site is meant to give information related to the 1993
(o)Mazda RX-7 Twin Turbo. Anything from rotary engines to wiring diagrams and turbo upgrades to tuning info, this site has it all! efini 93 rx7 13b anfini Turbo RX-7 Turbo RX7 turbo rx7 rx7tt rx-7tt As well as the Rotary Engine Pickup Truck aka REPU repu