Octane/Timing relationships

[K4fxd]

BUT what is the control octane number ?

There isn't. Whatever number you have then go with the chart.

So if it is at the edge of knock on 87 and you increase the air temp 7c you now need 88. Same if you started with 100 ect..

At least that is how I read it.

as far as needing one knock number per 1 degree of spark advance, that seems a bit conservative. Even knock limited.

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[engineermike]

Some they’re talking delta octane numbers the absolute value is irrelevant.

 

[engineermike]

Notice that 1 compression number is worth about the same octane as direct injection. Thus, the cr and di introduced together in the gen3.

 

[Jasonb543]

Learn to read spark plugs, the engine will show you.

 

[WildHorse]

Learn to read spark plugs, the engine will show you.

I literally just did that. Everything is primo. That Octanium sure leaves an orange-ish deposits though ha-ha.

 

[WildHorse]

Notice that 1 compression number is worth about the same octane as direct injection. Thus, the cr and di introduced together in the gen3.

All depends how that DI is used.

 

[engineermike]

All depends how that DI is used.

Can you explain?

 

[WildHorse]

Can you explain?

Is the DI active in conjunction the port injection at all times ? Or on only low load, low rpm ? Only WOT ? Only at WOT with port injection ?

 

[engineermike]

Is the DI active in conjunction the port injection at all times ? Or on only low load, low rpm ? Only WOT ? Only at WOT with port injection ?

Since I mentioned the gen3, I can tell you how ford does it if that’s what you’re after. Though my base case assumption and the assumption in the table is that di is added for the purpose of suppressing knock so implementing in ways that would not suppress knock would be, well, silly. I can also tell you that the Gen4 (if that’s what we’re calling it) has an additional table that adds borderline timing with gdi blend % and the values align well with the table.

 

[WildHorse]

Though my base case assumption and the assumption in the table is that di is added for the purpose of suppressing knock

So now we know.

Lot of tooners say the FORDS DI just gets in the way. And that theres better ways of tackling knock.

 

[engineermike]

Lot of tooners say the FORDS DI just gets in the way. And that theres better ways of tackling knock.

There is literally no other reason to add DI.

The easy-button for tooners is E85 because it basically doesn't knock and tuning DI is something most aren't familiar with.

 

[WildHorse]

There is literally no other reason to add DI.

Literally the Toyota D-4S & many others use PFI & DFI in conjunction.
So, it appears the knock suppression isn't the only reason.

 

[Joshinator99]

So now we know.

Lot of tooners say the FORDS DI just gets in the way. And that theres better ways of tackling knock.

There is literally no other reason to add DI.

The easy-button for tooners is E85 because it basically doesn't knock and tuning DI is something most aren't familiar with.

Literally the Toyota D-4S & many others use PFI & DFI in conjunction.
So, it appears the knock suppression isn't the only reason.

DI makes more power than PFI every day of the week and twice on Sunday. Check out Brian Tooley Racings videos on this, they did back to back dyno tests in the same engine using different fueling combinations, and the DI always made the most power. As they scaled in more PFI fueling, the power dropped accordingly. DI allows for more compression, less knock, and less air volume taken up carrying fuel. An all-DI engine will net roughly 10% more power than an all-PFI engine. The more you blend towards DI the more power you will make.

 

[Joshinator99]

The easy-button for tooners is E85 because it basically doesn't knock and tuning DI is something most aren't familiar with.

Could not agree more! Us Camaro guys are DI-only from GM and I can tell you the learning curve is very real, and so many GM owners still do not grasp it. Very expensive to upgrade too unfortunately.

 

[ice445]

Surprising that table gives so many octane points for altitude. I thought that was outdated info?

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