Question about Timing and Knock Sesnors

[TheShit]

Let's say you're in 4th gear (6spd) doing a pull at WOT and the knock sensor picks up something and it pulls timing.

1. How much timing can the computer pull?
2. Once it detects knock and pulls 'X' amount of timing, does it keep that timing value all the way until you are no longer at WOT?
3. If the system doesn't detect any knock, how does it know how much timing it can advance?

Sorry I know absoultely nothing about tuning, I just have questions.

Sponsored

 

[engineermike]

The timing control on these cars is fascinating. I'll answer your direct questions, then add a few more bits. I'm using a random 2021 Gen3 GT calibration to source the numbers, as they are different depending on year and exact model.

1. How much timing can the computer pull? The computer can pull up to 2.5 degrees per knock event, or up to 10 degrees total. Below 5080 rpm, it pulls the timing from only the offending cylinder but above 5080 rpm, if one cylinder knocks it pulls timing from all 8. All it takes is one knock event on one cylinder at high rpm, and it pulls a couple of degrees from all 8 and you usually won't have another knock event during that pull.
2. Once it detects knock and pulls 'X' amount of timing, does it keep that timing value all the way until you are no longer at WOT? No, it immediately begins adding timing again similar to how it would had it not experienced knock. There are "normal" and "fast" knock advance rates, as well, with certain criteria to decide which. A normal rate might be 6 seconds for 1/4 deg and a fast rate might be 3 seconds for a 1/2 deg, both at 7000 rpm. The rates are higher at low rpm.
3. If the system doesn't detect any knock, how does it know how much timing it can advance? The Ford logic calculates timing several different ways and they act as "limits". At WOT you are usually hitting the "borderline knock" limit, to which knock advance is added. Borderline knock is a function of rpm, load, cam timing (based on pre-mapped cam timing combinations), charge temp, coolant temp, and lambda. The logic also calculates a timing Preignition limit, Cylinder pressure limit, and MBT (max brake torque) timing. It commands the lowest of these 4 values. Preignition and cyl pressure are also a function of lambda, load, and rpm, while MBT is a function of cam timing (mapped points) as well as lambda, load, and rpm. It will stop advancing if it hits any of these limits due to the low-select logic. My experience is if you don't have knock you'll hit MBT next, but every now and then cylinder pressure limit. The logic also uses timing to reduce torque, like for transmission shifting and other reasons. This will also reduce timing to some lower number regardless of knock activity.

The Gen3 logic has some FFV functionality where it can increase borderline timing as a function of learned ethanol %. The Gen2's didn't have this capability. This comes in really handy when flex tuning.

And finally there's learned octane/octane adjust, where it can add to or subtract from the initial borderline number as a function of learned knock activity. Ford doesn't use it on the Gen3 in any model as far as I know. I tried to make this work on a Gen3 and had no luck using HPT. I have not attempted again using PCMTec but I tend to think it can be done.

 

[GTP]

I don't care about the extra HP gained from using high octane pump gas during HPDE track days. But am I taking any risks to my engine given the higher RPM/loads if I use regular 87 octane gas?

 

[Aless_andro00]

Let's say you're in 4th gear (6spd) doing a pull at WOT and the knock sensor picks up something and it pulls timing.

1. How much timing can the computer pull?
2. Once it detects knock and pulls 'X' amount of timing, does it keep that timing value all the way until you are no longer at WOT?
3. If the system doesn't detect any knock, how does it know how much timing it can advance?

Sorry I know absoultely nothing about tuning, I just have questions.

Just saw your post. Well, the engine's computer can change how early or late the spark happens to prevent damage from knocking, which is a bad type of combustion. How much it changes this timing can be different for each car and depends on the computer's programming and the engine's design. It might adjust the timing a little or a lot, usually between 1 to 15 degrees.
After the computer notices knocking and changes the timing to make it safer, whether it keeps this adjusted timing until you stop pushing the gas pedal all the way down depends on the car's programming. Some cars' computers might quickly try to go back to the original timing to keep the engine running well if it stops detecting knocking. Others might wait longer or until something else changes, like how hard the engine is working, the engine speed, or if you shift gears. The goal is to keep the engine safe while trying to make it perform as well as possible.

Sponsored