Wideband O2/Datalogit Tuning
Stoichiometric or Theoretical Combustion is the ideal combustion process during which a fuel is burned completely. A complete combustion is a process which burns all the carbon (C) to (CO2), all hydrogen (H) to (H2O) and all sulfur (S) to (SO2). If there are unburned components in the exhaust gas such as C, H2, CO the combustion process is uncompleted (taftan) Approximately 14.7 parts Air to 1 part Fuel (14.7:1) for the perfect complete combustion.
Remember: when the term 1 bar is used to describe pressure what most forget to state is that it is assumed they mean “above atmospheric pressure.” Naturally the atmosphere has pressure (1 BAR approx 14.7 PSI) but this is assumed constant. Stating a turbo “kicks out” 14 PSI that is actually 14 PSI more than the atmospheric hence 14.7 PSI is technically 2 BAR
101.325 kPa = 1 ATM
100 kPa = 1 bar
200 kPa = 2 bar = 14.7 PSI (referred to 1 bar assuming it is understood to be 1 bar above atmospheric pressure)
Goals of a tuner:
For any given moment have the A/F ratio, Load, and RPM to make calculations and then output the corrected amount of fuel for the desired A/F ratio in those same conditions .
- high 14′s up to “0 PSI” AKA atmospheric pressure (1 BAR)
- mid 12′s up to 6 PSI (1.4 – 1.5 BAR)
- mid 11′s up to 14.5 PSI (2 BAR) and above.
Fuel related links:
Detailed information on both Gasoline/Ignition
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
What is DETONATION?
Typical timing advances:
- 30 to 35 deg advance to 90kpa (0.9 BAR)
- 20 odd up to 120kpa (1.2 BAR, 3 PSI)
- 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*
- STOCK PORT 20-23 deg advance …lowest effective “dynamic” compression at max power.
- STREET PORT 15-17 deg advance…midrange effective “dynamic” compression at max power.
- PERIPHERAL PORT 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
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.
This is the FJO Wideband O2 sensor kit which is used as well.
Lambda-BoyStandard Air Fuel Ratio Meter
Innovate Motorsports 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 resources only)
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 the goal.
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.