Questions on AFR Tuning for BRZ/GR86 During WOT

Hi everyone,

I’ve been working on tuning my BRZ/GR86 and encountered some questions about AFR (Air-Fuel Ratio) settings during wide-open throttle (WOT). I’m hoping to get some insights from the experienced members here.

In the stock calibration, I noticed that the factory target AFR for WOT is typically set around 12.2–11.9, but based on actual logs, the AFR often ends up being richer, usually around 11.5 (using the factory-calibrated sensor).

I have two main questions:

1. Ideal AFR and Ignition Timing Combination

If both of the following configurations can achieve similar power output:

• Option A: A leaner AFR (e.g., 12.5) paired with later ignition timing.
• Option B: A richer AFR (e.g., 11.5–11.8) paired with earlier ignition timing.

Here’s what I understand:

• Leaner AFR + Later Ignition Timing: Could lead to higher exhaust gas temperatures (EGT) and potentially increase thermal stress.
• Richer AFR + Earlier Ignition Timing: Might reduce EGT but could increase the risk of knock.

2. AFR Range for Naturally Aspirated Tuning

For naturally aspirated engines, is it normal for the actual WOT AFR to fall within the range of 11.0–12.0? Could running richer in this range lead to carbon buildup or other long-term issues?

From my understanding, an ideal AFR for NA engines during WOT is typically around 12.5, but is it common to see richer values in practice? Should I aim to adjust this, or is this range acceptable?

I’d greatly appreciate any insights or advice on these topics. If anyone has experience or log data to share, it would be fantastic to compare notes and learn from your experience.

Thanks in advance for your help!

Arvin,

First, what you're seeing in stock form is normal for this car. All of them run richer than the open loop target at WOT.

Time spent at WOT isn't a significant portion of total engine operation in a street vehicle, so I don't suggest making choices about ideal AFR over a small range based on potential carbon buildup. Also consider that you're considering options which are leaner than stock, and stock the cars don't exhibit severe buildup issues. In a race application, engines generally don't last long enough to worry about buildup that may become significant at say 100k miles.

I'm simplifying for the sake of trying to provide some info without complex discussion, but I suggest thinking of shifting ignition timing moving the heat more than increasing or decreasing it. More timing advance, more heat in the combustion chamber, less in the exhaust. Less timing advance, less heat in the combustion chamber, more in the exhaust.

It's vital that you don't forget the OE tune is designed to protect not only the engine, but the emissions systems. The catalyst can become overheated if you aren't careful, so monitoring catalyst temperature with probes is part of a thorough calibration process.

You always want a balance, not being too aggressive on lambda or ignition timing. Being too aggressive on either can cause harm, but knock can cause damage in an instant, and heat requires far more time to cause harm. Keeping knock sensitivity at stock values will help you identify knock. It works pretty well on that vehicle.

Hi Mike,

Thank you very much for your detailed response! Your explanation has deepened my understanding of ignition timing and its effect on heat distribution. I truly appreciate your guidance on balancing parameters during calibration.

I understand your point that knock is the primary concern compared to accumulated heat or carbon buildup. During the tuning process for this car, I’ve noticed that this model is quite sensitive to heat. Specifically, when the engine temperature rises, even with the stock tune, I observe 1-2 degrees of timing retard at high RPMs. Additionally, during transient operations in the 2,000-3,000 RPM range, there is a degree of timing retard (around 0.5-1 degree).

Our local fuel is 98 octane, which I believe should provide better knock resistance compared to lower-octane fuels. However, given the sensitivity of this engine, should I be concerned about this knock behavior and make adjustments to address it, or is this level of timing retard so minor that it doesn’t warrant significant changes?

And now, after cooling exhaust upgrade (Oil cooler, Ventilation underguard, de-cat front pipe, and 150 cells headers, my car runs good with 12.0 AFR from 3500 to 6500 (Ignition timing from 22 to 26) and 11.8 AFR from 6500 to top end (Ignition timing from 26 to 24.5). knock correction value and knock correction fine value stay at 0 in WOT, but occasionally get 0.5 to 1 ignition retard during transient in 3000-5000. Should I take care of the minor knock feedback or not.

Once again, thank you for sharing your valuable experience and advice! I look forward to hearing more of your insights.

Best,

Arvin

Arvin,

Occasional knock of about 1 degree in transients may be acceptable, but it's really up to your comfort level in terms of how much knock response you decide to allow.

I don't know which generation car you have, but on the Gen2 cars there are multiple ignition tables for different amounts of throttle, so be mindful that you may have reduced timing in the high throttle table, but not a mid or low throttle table that's actually active during an event.

Yes, the various temperatures impact the ignition timing knock limit on your pump fuel, so compensations will need adjusted. Some choose to tune for consistency of power output, while others choose to try and get the most out of each combination of conditions.

Aside from timing, knock in transients may instead have more to do with fueling error than timing. Perhaps monitored lambda goes lean of target when you apply throttle. You may need to make fueling adjustments i.e. accel enrichment.

Hi Mike,

Thanks again for your patience. Yes, I am tuning Gen2. But I haven't find the ignition tables for different amount of throttle in my Ecutek software. Is it an undefined map in ECUTEK?

Another very interesting thing is that the ignition coolant compensation didn't work on my car. In the ignition timing coolant temp compensation table, -9 degree will be pulled out in 90 ℃ coolant temp, it didn't pulled out at all. The acutal ignition timing is equal to Base map+Advance-AIT compensation-Knock retard.

Because I will track my car, I think will take care of the 1 degree of retard in mid rpm transient. I will first try to decrease the base map first as I can't find the ignition vs throttle table

I really appreciated for you kindly remind and suggestion!

Best,

Arvin