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Discussion and questions related to the course Practical Standalone Tuning
I am running a BP4W 4 cylinder 1.8L engine paired with a haltech elite 1500 running 72mm DBW throttle body. Stock flywheel is 16.2 lbs.
What I want to do is when I let off the clutch without giving it throttle the engine hold enough power to creep without stalling. Right now my throttle is at 4.2% max idling and my open loop is about 50% to idle at 900rpm. Basicly to achieve the 900rpm idle the throttle is at 1.8-2%. Output max is 100%. Zero demand ignition is at 15 degree.
Stall off set is set at 200rpm so if the clutch is released the engine will dip to 700rpm then the ecu will open the throttle to 4.2% and rev the engine to 1400 rpm to prevent stalling. The issue with this is when at 1400 it will bounce back to about 700 then back and forth until the car has moved enough to not stall. It makes it jerky.
My theory is if I set me max throttle to 2.5% and have the ecu control idle all the time at about 80-90% max out put when I release the clutch the engine would go up to no higher than 1000-1050 rpm and it bounces less.
The questions are:
1. Would having DBW Throttle output at 80-90% idling ideal? Or should I just drop the output max?
2. What's the differences between Output Max and DBW Max Position? I know Output Max is related to DBW Max Position but which equation does the Output Max control?
3. Should I increase zero demand ignition more so the engine has more power to overcome stalling when I let off the clutch?
You generally want ignition timing to do the bulk of the instantaneous idle control since it can affect torque very quickly and then throttle (which is slower at increasing torque) takes care of longer-term offset. I dont know what options Haltech has for the idle control, but that is the general strategy you want to think about in the back of your mind.
So run idle ignition timing relatively retarded for the normal warm idle - say 5deg BTDC provided it still runs nice. This gives you a bigger margin between the normal timing and MBT so when a sudden load increase occurs the ecu can add a lot of extra torque quickly to prevent the stall.
I'm presuming that that is not the standard throttle body that you are using? 72mm is a large throttle for that size engine, a 58~62mm throttle would have been suitable for the airflow requirements of that engine. Having too large a throttle body makes idle and idle transient conditions tricky to get right, as you are working with large changes in mass flow relative to a small change in the throttle angle. Going from a 60mm throttle (standard throttle size for the BP engines that I can find) to the 72mm unit that you are using is a change of 44% in throttle opening area, at low openings this requires a much smaller throttle angle to maintain engine speed, and a larger reaction to small changes in this angle.
That the engine is idling at 2.5% throttle opening says that the throttle is over sized for the airflow requirements. You will most likely find that setting the maximum throttle opening angle to less than 100% (plate 90 degrees to the airflow) will not change available power. I know with the Toyota 86 that setting the throttle plate to the correct opening position (the 90 degrees to airflow position) and then using the ECU setting to restrict the opening to 80% of this angle will result in no loss of power on a dyno, nor will a professional race driver detect the differences in driveability or have it reflect in the lap times.