Ignition cut rev limiter possible?

[mituc]

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).

[riffy]

This feature is not currently available, we would have to investigate how much work it is to add something like that.

Any possible update on the status of that if it's been looked into?

[Walle]

any reason why we couldnt do a "gheto" revcut limiter in the ignition tables ?
adjust the rpm axis where the max RPM will become the rew limiter rpm, and one before it where it is still inactive.

I dont have a table in front of me now but in principle if rev cut is at 9000 (oem) increase the rev limit (fuel cut)
adjust the axis on the ignition tables that the max rpm is 9050 rpm and there a big retard is made (where it wont ignite the mixture lets say -70-90deg) and have the next below it at say 9000 rpm (this gives 50 rpm hysteresis) thought this might "melt" the exhaust fuel cut could be given at 9100 rpm maybe ?

dwell needs to be calculated so we are sure that the next proper ignition will be made possible with "full" power in coils to not have a missfire

Please comment. I might be tottaly of coming from diesels with this logic where injection is controlled like this. that gives a hard rev limiter on them.

[Walle]

thought simplest solution is to rais the rev limiter and avoind hitting it. the power drops of anyway so you will feel it before it "comes"

[wcs]

Just read an interesting post from Brettus on the RX8 club about the Rev Limiter cut.
He did a bit of a thread Resurrection, however the thread is short and his post is worth reading.

https://www.rx8club.com/rx-8-discussion ... em-143791/

[d-LoiX]

That seems to create a very lean condition on NA after the limiter?
Besides not taking it to the limit what is recommended?
I increased the limit to 9300 (to shift before it)
I also disabled completely Decel Fuel cut (to avoid lean when shifting) but from 2nd gear to 3rd gear at high RPM shift I believe the engine chokes for a second due to too much fuel.

[McTinkerson]

That seems to create a very lean condition on NA after the limiter?
Besides not taking it to the limit what is recommended?
I increased the limit to 9300 (to shift before it)
I also disabled completely Decel Fuel cut (to avoid lean when shifting) but from 2nd gear to 3rd gear at high RPM shift I believe the engine chokes for a second due to too much fuel.

Have you datalogged this? Because I have an it isn't a rich condition. It's the fuel cut kicking in. The DFCO table doesn't work.

[d-LoiX]

I haven't yet! Car is on the shop for a 5.1 ring & pinion.
But how come the DCFT does not work? why is it even there then?

DCFT is table for coolant temp vs RPM saying above that RPM decal cut will kick in at that specific coolant temp.
I put 9500 above 80ºC so that would disable decel fuel cut. with the stock table set up it did not happen.

I will get the car in a couple of weeks and do proper testing as soon as I can.
One would thought if table exists on a 400 usb sw then it should work no?

[Walle]

Just read an interesting post from Brettus on the RX8 club about the Rev Limiter cut.
He did a bit of a thread Resurrection, however the thread is short and his post is worth reading.

https://www.rx8club.com/rx-8-discussion ... em-143791/

someone from versa should follow that up and maybe enable a function before mazda Edit, as there has been a lot of progress and data from Bretus

[malijames12]

bump