Re: Ignition cut rev limiter possible?
Posted: August 17th, 2021, 4:26 am
So coming back to this, I have something implemented in my tunes for a long time now, to drop the timing abruptly beginning with a certain RPM. However because of how ECU tunes logic works, the timing values are being interpolated from the last RPM point where they were set to a proper value and the next RPM point we have control on and we have them dropped to implement some sort of soft limiter/cut. So it's not sudden/abrupt, it's progressive.
The problem with this as a setting in the actual calibration tables of the tune is that if you want to cut the engine at, say, 7000rpm, if you have proper timing values at 6500 and very low values at 7000 basically you are robbed of 300-400rpm from the engine power band. This is why:
- if, say, you command 16 degrees of timing at 6500rpm;
- ...and -20 degrees of timing at 7000rpm;
- at 6750rpm you'd have roughly the average between the two (-2) while the optimum and safe timing at that RPM is probably 16.5-17 (having 16 degrees @ 6500rpm as a reference, this varies from engine to engine, with fuel, type of pistons or rotors, exhaust mods, and so on).
- basically you can calculate the timing and load in each RPM point between the two references because they will be on the same segment defined by those two points, in our case with the coordinates of the RPM and timing (it can be RPM and load depending on the used strategies - I use both).
So it's still doable but not as elegant as having the ignition cut at a certain RPM.
To implement this limit directly in the ECU calibration I basically command a ridiculously low timing value and load value above those RPM I don't want to go above, and the rev limit is set a tad higher to avoid the engine fuel cut from the default rev limit strategy.
So this is how I implemented it in my case. It's a piston engine, I have no idea if it will work for you as well or not, but it's an idea.
Probably because on some models the rev limit is at 9000rpm and the lead and trailing ignition tables also end at that RPM some scaling must be required to make the ignition tables go above that RPM by the desired amount (also considering the eventual rev limit increase, if it's the case).
The problem with this as a setting in the actual calibration tables of the tune is that if you want to cut the engine at, say, 7000rpm, if you have proper timing values at 6500 and very low values at 7000 basically you are robbed of 300-400rpm from the engine power band. This is why:
- if, say, you command 16 degrees of timing at 6500rpm;
- ...and -20 degrees of timing at 7000rpm;
- at 6750rpm you'd have roughly the average between the two (-2) while the optimum and safe timing at that RPM is probably 16.5-17 (having 16 degrees @ 6500rpm as a reference, this varies from engine to engine, with fuel, type of pistons or rotors, exhaust mods, and so on).
- basically you can calculate the timing and load in each RPM point between the two references because they will be on the same segment defined by those two points, in our case with the coordinates of the RPM and timing (it can be RPM and load depending on the used strategies - I use both).
So it's still doable but not as elegant as having the ignition cut at a certain RPM.
To implement this limit directly in the ECU calibration I basically command a ridiculously low timing value and load value above those RPM I don't want to go above, and the rev limit is set a tad higher to avoid the engine fuel cut from the default rev limit strategy.
So this is how I implemented it in my case. It's a piston engine, I have no idea if it will work for you as well or not, but it's an idea.
Probably because on some models the rev limit is at 9000rpm and the lead and trailing ignition tables also end at that RPM some scaling must be required to make the ignition tables go above that RPM by the desired amount (also considering the eventual rev limit increase, if it's the case).
fuel cut could be given at 9100 rpm maybe ?
