Welcome to our introduction to our VE tuning.
As far as we know, Autronic were the first guys in the aftermarket world to do VE tuning. We followed in December 2009 and since then other aftermarket ECU manufacturers have followed.
The main benefit is that it allows you to generate a base map really quickly. Even if you don’t have all the details of your injectors, it’s still a lot quicker than guessing millisecond values and allows you to more easily see incorrect fuel map values.
Here’s the theory: each time the engine rotates through its cycle (720 degrees or a 4-stroke, 360 degrees for a 2-stroke), it draws through its swept volume worth of air, multiplied by its volumetric efficiency. For example a 4 litre engine operating at 80% efficiency would draw through 3.2 litres of air in 2 crank revolutions.
Knowing this, as well as the manifold air pressure (MAP) and air temperature, the ECU can calculate the mass of air that’s gone through the engine in one cycle.Knowing this, and the target AFR, the ECU can work out how much fuel to inject. Knowing the amount of fuel to inject, the injector flow rate and the injector dead time, the ECU can work out the injector duration in milliseconds.
So here are the steps to set it up:
1. Set the engine capacity in cc
2. Set your injector type.
Currently we have characterisation for the ID1000s and Deatschwerx 720s hardcoded in the ECU. If you’re using either of these and primary injection only (no injector staging), then you can select the injector type, type in the fuel pressure in kPa and select whether your fuel pressure regulator is manifold referenced or not, and the ECU will work out the flow rate and dead time (also called “offset”) based on the fuel pressure.
Otherwise, if you’re using ID725s, 850s, 1000s or 2000s, you can go to the primary dead time setting
select the injector type, enter the fuel pressure and select “set”. This will set the dead time based on the injector type and fuel pressure, and also set the injector flow rate.
If you are not using staged injection, Then make sure you set the primary 2 and the secondary injector sizes to zero so that the ECU doesn’t run in staged injection mode.
If you are using other sorts of injectors, then enter the flow rate in the primary injector flow rate, and enter the dead times in the primary dead time table. A value of 1 here corresponds to 10 microseconds, so 100 is one millisecond.
3. If you’re using staged injection, then the injector type must be set to dead time / flow. If you’re using ID injectors then you can go to the dead time settings and select the injector type and fuel pressure and click set and the software will set those for you. Otherwise enter the dead times and flow rates provided by your injector manufacturer at your nominate fuel pressure.
If you’re using only 2 stages of injection, as on the RX7 and the series 2 RX8, then just enter the values in the primary and secondary injector settings.
If you’re using 3 stages of injection, as on the series 1 RX8, also enter the primary 2 injector size. Ensure that your target AFRs are set up to roughly where you want them.
From there, start with the fuel map at all constant values in the range of 80 to 100. This will get most engines running quickly, and from there it can be tuned as usual. Note that from here, not only do you get a lot more resolution than using milliseconds alone, because the values are scaled by the manifold pressure.
One final point, when you’re tuning, the AFR or lambda field in the gauges window gives you 3 values. The first is the measured AFR; via either the serial wideband or an analogue input. The second is the AFR measured from the analogue input. The third is the target AFR.
When you’re tuning, you need to adjust the value in the fuel map to get the AFR reading to match the target AFR. Once this is done, you can change your target AFR and the ECU will automatically change the injector duration to achieve the new target AFR.
