Quote:
Originally Posted by Ecky
I can confirm the Honda K series (at least the A and Z engines) use fixed ignition timing. They use MAP rather than MAF, and ignition happens based on a set of tables.
Something I haven't yet figured out is how far ignition timing should be advanced at part throttle, and it's quite hard to test for even with a load dyno. More advance is not always better. Ignition advance refers to how many degrees *before* the piston reaches TDC it fires, meaning the piston is still moving toward the top of the compression stroke. Pressure is building and during that time it's actually doing negative work, trying to spin the engine backwards.
On most engines you can't over-advance ignition timing at WOT on pump gas. Before you have advanced timing enough to get peak pressure at the most efficient angle (which I've read is typically 14-16 degrees but may vary with flame speed), pressures get high enough early enough that the remainder of the charge in the cylinder ignites from compression ( = knock) while the piston is still rising. However at part throttle cylinder pressures are lower, and with lower compression engines (especially turbos) or those with great combustion chamber designs, it's almost certainly possible to over-advance ignition timing without running into knock.
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That is very helpful, thank you for the information! I presume that the D series engines uses fixed timing tables too then. Another question- Since the timing tables are fixed, there would be no benefit whatsoever to using a higher octane fuel than recommended since the ECU won’t advance the timing anymore anyways. Is that correct? Also, under normal conditions, would there ever be any knock for the sensor to pick up to retard the timing?
Also, does the IAT affect the ignition timing? If it does, I presume maybe I could get a little more power by installing a resistor in the IAT wiring harness so the ECU thinks the air is colder than it is and advances the timing more if I use high octane fuel?