RomRaider

As I understand the knock control strategy for recent (CAN bus) ECUs, the stock ignition advance is designed to stay within the anti-knock zone:

From the factory shop manual (2011 G37)

The knock sensor retard system is designed only for emergencies.
The basic ignition timing is programmed within the anti-knocking zone, if recommended fuel is used under dry conditions. The retard system does not operate under normal driving conditions. If engine knocking occurs, the knock sensor monitors the condition. The signal is transmitted to the ECM. The ECM retards the ignition timing to eliminate the knocking condition.

With this in mind, would the ECU change the ignition advance IF 94 octane fuel was used?
Would the engine make more power with 94 octane vs 91 octane?

So for 350z’s we have Cold Ignition Trim, High Octane Ignition Trim, and High Detonation Ignition Trim. The High Octane ignition trim is setup for 91 octane here in America. I know European Z’s can be setup for 93 octane though. But putting in higher octane fuel than the ignition map is setup for won’t yield and power gains. Although, you could just bump up the ignition timing all around by a bit to compensate for the anti-knocking zone being raised. Since our timing maps are in burn time, it’s actually pretty easy to get it dialed in like that haha

Hey Pytrex,
Thanks for the excellent clarification!

Are you aware of any "dynamic advance" that is built into the stock ECU?

No, Nissan has not made an ignition map in "burn time". https://www.romraider.com/forum/viewtopic.php?f=65&t=15017

You've been through the A2L, you should know!

Generally, no. The maximum amount of advance you'll get is calculated from the "Mean Best Torque (MBT)" amount and then whatever the trimming map adds or removes. The ECU uses the knock sensor to detect fuel quality, but it will never give more advance than the cold or high-octane maps.

I see people talking about how the ignition timing on the VQ37 is much more adaptable. Perhaps they have something else going on there, but the trimming maps are similar so I wouldn't expect increased advance. Especially with the risk of damage to the engine, Nissan wouldn't embed that risk in the code.

In my defense, we originally thought it was burn time and I haven't added anything ignition related besides limiters xD Plus I've been focused on finding the maps before figuring out what the hell these monstrosities can do haha But eventually I am gonna go into IDA and figure them out through the functions. Luckily ZB060 lines up almost perfectly with CF48D in terms of the functions. The values and numbers are a bit different, but the lines and commands are pretty much identical.

Off topic but any advice on figuring out scaling for the few maps that don't follow the A2L's scaling?

I think you are correct about the VQ37 timing being a little different. From the UpRev Nissan Tuning Guide, page 7



"On the newer vehicles equipped with VVEL, the ignition advance algorithms rely heavily on knock sensor feedback.

In many cases it is not possible to make the ECU run more advance because as soon as you increase the values it hears something on the knock sensor and adjusts accordingly.

For VVEL vehicles you WILL still have to pull timing for forced induction applications so that it won’t ping before it has a chance to do any learning. However for NA applications about all you can do is pull back the high spots and smooth the table out. The ECU will do the rest on its own.

In our testing we found that pulling LARGE values from the main ignition table caused a LARGE power drop on the first run, but after a few consecutive runs the ECU would advance the ignition right back to where it was before based on knock sensor feedback."



If the ignition timing relies "heavily on knock sensor feedback", I wonder if the ignition timing would change (advance) if 94 octane fuel was used.

I might try a tank of 94 octane and after 100 or so KM, data log ignition timing with different engine loads.
Based on past data logging (many, many runs!!) at wide open throttle, in second gear the ignition timing is around 22-23° BTDC @ 3500-4500 RPM and ramps up to around 28° @ 7000 RPM with 91 octane.

I understand fuel temp, barometric pressure, and air intake temp are inputs into the ignition timing calculation, so I may not be able to see any correlation... but you don't know until you try

I would suggest finding the most similar / units-related CID parameter you have, and trace xrefs starting from your map input values and from the CID until they "meet".