Octane/Timing relationships

[WildHorse]

So say going from 91 to 93 octane, and all things being equal, how much timing can you add below 4k rpm and above 4k rpm ?

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[horsepower addiction]

It’s not that simple

 

[WildHorse]

It’s not that simple

K lets make it simple ... @ WOT.

 

[loucas-2021]

Found this, hope it helps. Can't guarantee it is accurate but might be worth considering.

"Switching from 91 to 93 octane fuel allows for more aggressive ignition timing due to the higher resistance to knocking. Generally, you can advance the timing by about 2-4 degrees across the RPM range12.

Below 4,000 RPM, you might see a timing advance of around 2 degrees, while above 4,000 RPM, you could potentially add up to 4 degrees12. However, the exact amount can vary depending on your specific engine setup and tuning."

 

[K4fxd]

If you look at Fords MBT tables thats probably it. I have never gotten full MBT on 93. I've had to use 100.

Lots of tunes are running 30 and the cars are not blowing up.

With the coyote's chamber and head design I don't see any improvement over 31. And more likely 30, in fact 28 might be min timing for max torque.

 

[GregO]

K lets make it simple ... @ WOT.

The trick in measured distance drag racing or speed record attempts is knowing when to pull timing back to gain MPH through the two eyes.

 

[WildHorse]

The trick in measured distance drag racing or speed record attempts is knowing when to pull timing back to gain MPH through the two eyes.

Right. But at the end of the 1/4 I'm in 4th around 6600 rpm. Pulling timing in any gear other than 1:1 or overdrive is detrimental.

 

[K4fxd]

But at the end of the 1/4 I'm in 4th around 6600 rpm

You need more gear.

 

[WildHorse]

You need more gear.

3.73's.
SHity 60s and 1/8 mile was the culprit. With good tires I'm going through the traps at 7200 or so. Still in 4th.

 

[K4fxd]

With good tires I'm going through the traps at 7200 or so. Still in 4th.

Thats better.

I calculated mine out and for 1/4 mile i was best with 3.55 or 4.56, depending on which gear I wanted to top out in.

 

[engineermike]

Found this some time back in a research paper.

 

[K4fxd]

That chart is kinda worthless without the caption.

What does it mean?

 

[WildHorse]

What does it mean?

Nothing without a baseline to compare. Like whats the control ? 80 octane ? 85 octane ?

 

[engineermike]

1 ONR is one octane number. Top row is spark advance at knock, so 1 octane number is worth 1 deg timing advance when knock limited. This was found to be true between 0 and 30 deg timing. It’s a really useful chart and I’ve found it aligns well with the oem cal.

 

[WildHorse]

1 ONR is one octane number. Top row is spark advance at knock, so 1 octane number is worth 1 deg timing advance when knock limited. This was found to be true between 0 and 30 deg timing. It’s a really useful chart and I’ve found it aligns well with the oem cal.

I understand that. BUT what is the control octane number ?

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