parker_siJun 9, 09:50 AM

Ignition Timing & Knock Control: Tuning E85 map vs 93 Octane on FA24 engine.

Running an EcuTek tune on my BRZ (FA24). On 93 octane, my Fine Learning Knock Correction (FLKC) drops to -1.4 degrees around 5500 RPM under high load. Swapping to E85 (tested at E78) completely clears the knock and allows us to advance timing by 4 degrees. Is the FA24 dynamic ignition timing logic too aggressive for standard pump gas, or is my tuner pushing the limits?

Discussion

7 comments

tyler_boostedJun 11, 02:57 AM

I've seen stock FA24s pull timing on 91 octane all day long. Subaru tuned these engines very close to da knock limit for emissions and fuel economy.

brody_tunedJun 12, 02:23 PM

Who tuned it? If it's a generic shelf map, they usually push timing too far down low to make the dyno sheet look good. -1.4 FLKC is minor, but if it drops to -2.8, back off.

tanner.driftJun 13, 11:45 PM

Are you logging Feedback Knock too? If FBKC is 0 and only FLKC is dropping, the ECU just learned a soft spot. It's probably noise from the transmission or header.

lsx_sammyJun 15, 03:35 AM

FA24 has a high compression ratio (12.5:1). 93 octane is right at the thermal limit for direct injection at high load. FLKC of -1.4 is just the ECU doing its job. It's safe.

wyatt_hemiJun 15, 04:14 PM

E85 has way higher latent heat of vaporization. It cools the intake charge so much that you can run 4 degrees advance without detonation. The dynamic advance map is built for E85 anyway.

phoenix_car_sceneJun 17, 11:44 AM

🔧👨‍🔧

brody.dieselJun 17, 03:38 PM

Make sure your fuel trims aren't maxing out on E85. The direct injectors on the FA24 run out of headroom around E80 if you're pushing past 22 degrees of total timing.