Discussion and questions related to the course EFI Tuning Fundamentals
I've got a Radical SR8 that I've got running with a MoTeC ECU using the GPR package with Geartronics extensions. All is well except idle. When I set offset and scale for the Jenvey DBW servos (one per bank), I can get them pretty close -- within a percent or two. And for track use, that's plenty good enough. But at idle, a couple of percent makes a big difference in air flow from bank to bank -- 20/30% air flow difference.
I'm wondering if anybody has a procedure for getting the throttle percent to match airflow across dual servos, especially at low blade angles such as idle.
I would be adjusting the linkage with Unisyn to get the airflow the same for a given throttle area target. Another way is the use the throttle test - set a fixed Throttle Test Aim, turn off Closed Loop Fuel and adjust the linkage while monitoring the lambda readings on each bank. The airflow will be very close when the lambda values are the same on each bank. Might make the Fuel Mixture Aim a bit richer for smoother running during this test, then return it to it's previous values.
Thanks for the response. I've got flow meters I can use to get the air flow to match, but I was thinking that would affect the throttle closed offset value and cause other problems. I'm eyeing the throttle area table, and wondering if setting up some extra fidelity there with some tweaks might work.
The throttle closed offset value is determined at each startup. I would not change the actuator servo motor position, only the linkage from the servo motor to the ITBs. So both DBW actuators would be at the same throttle position (say an average of what you are currently finding when idling), and you would adjust the linkage so that both are flowing the same amount of air for that throttle position.
Yes, got it! I did a similar thing: I slowly closed the throttle stop on the rich bank (1/4 turn per iteration), then reset the offset and scale for that bank. The lambda values slowly converged (as did the throttle scale percentages, which showed that the rich bank was less open than the other bank), and all the volatility in the rich bank went away.
Now I've got some idle tuning to do, but balanced banks should make that an easier process.
Excellent! I bet that engine sounds sweet!