Octane/Timing relationships

[WildHorse]

There is literally no other reason to add DI.

Also found this:
Peter Dowding, Ford’s chief engineer of powertrain gasoline systems, revealed a different strategy. Ford uses PI alone at idle and at low rpm for smooth, quiet, and efficient engine operation. As rpm and load increase, fuel delivery becomes a programmed blend of PI and DI. In contrast to Toyota’s methodology, Ford’s PI is always operating, responsible for at least 5 to 10 percent of the fuel delivery.

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[engineermike]

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

Actually...it is. The Toyota 3.5 D-4S (my wife coincidentally owns one) is 11.8/1 compression. They are trying to milk every bit of fuel economy possible and one sure-fire way to do that is to raise the compression ratio. But I'd say that the overwhelming majority of Highlander owners put the cheapest 87 they can find in the tank. They run DI so they can retain decent spark timing while at nearly 12/1 compression on 87 octane.

 

[engineermike]

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.

It took me a lot of time, lots of tuning iterations, and a few dyno sessions to get comfortable with it. I upgraded to the XDI pump as well. You have the HP rail pressure, SOI angle, EOI angle, and max injection angle. Every one of those has a reason, limitations, etc. I had to figure them all out. I lost 100 hp from having EOI too late. Once I was done, I found I could get a lot more from the stock GDI system with just tuning.

 

[engineermike]

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 I thought that was outdated info?

Altitude does reduce knock, but it does so in a way that is seamless in the Ford logic. Higher altitude reduces engine load, which increases borderline spark timing.

 

[ice445]

Altitude does reduce knock, but it does so in a way that is seamless in the Ford logic. Higher altitude reduces engine load, which increases borderline spark timing.

Interesting. So basically the fuel is still getting maxed out.

 

[markmurfie]

Cold start emission reduction is greatly improved with DI/ PI blending. That was the main reason given by Ford for adding it iirc. They didnt go full DI as the PFI keeps carbon build up on the valves down. They use PFI heavily and almost never use DI with every day normal driving which is OEMs main focus.
Any performance gains from DI compared to PFI is not worth the complication if that was the only goal.

AS for octane/ timing relationship
The ecu can learn octane number and the eco boost with OAR do modfy for the octane number they think is in the tank. While the knock learn range is about 10*, it only modifys the borderline +/- .5* to 1.25* for a total of 1* to 2.5* for the range of octane ratings in various RPM /load conditions, from what I have seen.

 

[engineermike]

Also found this:
Peter Dowding, Ford’s chief engineer of powertrain gasoline systems, revealed a different strategy. Ford uses PI alone at idle and at low rpm for smooth, quiet, and efficient engine operation. As rpm and load increase, fuel delivery becomes a programmed blend of PI and DI. In contrast to Toyota’s methodology, Ford’s PI is always operating, responsible for at least 5 to 10 percent of the fuel delivery.

Let me just add some real data to this. This is a stock 2019 Coyote GDI blend table:

2024 is very similar.

And for 2024, this is the borderline knock timing adjustment table:

The implication here is that DI does more for you at low rpm than high. I suppose evaporation time plays a part here. Also interesting is that once you get above 50% blend the returns are little to none.

The reason they run high or 100% port at low load is simply that the knock suppression is not needed to achieve MBT due to low cylinder pressures. PFI has better cold starting, idle characteristics, and particulate emissions, so they use it when they can.

Someone smarter than me told me that they never go to 100% GDI because, once turned off, upon coming back on the first one or two PFI injections just wet the port and valve so you go lean for a couple of cycles.

 

[engineermike]

Interesting. So basically the fuel is still getting maxed out.

If I understand this correctly, yes. If you log borderline, MBT, and timing while driving around you see that it rides on MBT up to a certain load. Depending on rpm, this could be under .4 - .6 load it rides on MBT the whole time, but above that it starts getting knock limited. At high altitude, you'd still be above .6 at WOT, so it's still usually knock limited.

 

[engineermike]

Just another tidbit, when PBD interviewed that guy Jerry something, former Ford engineer, he pointed out that engines designed from the ground up for GDI can run just GDI. But engines retrofitted with GDI need to run both. It's an interesting thought, but the Ford 3.5 Ecoboost, Coyote, and the Toyota 3.5 were all PFI engines with GDI added later and they all run both. But the Ford nano, 2.3, etc were designed to be GDI engines from a clean sheet and all run just GDI even currently.

 

[markmurfie]

Let me just add some real data to this. This is a stock 2019 Coyote GDI blend table:

2024 is very similar.

And for 2024, this is the borderline knock timing adjustment table:

The implication here is that DI does more for you at low rpm than high. I suppose evaporation time plays a part here. Also interesting is that once you get above 50% blend the returns are little to none.

The reason they run high or 100% port at low load is simply that the knock suppression is not needed to achieve MBT due to low cylinder pressures. PFI has better cold starting, idle characteristics, and particulate emissions, so they use it when they can.

Someone smarter than me told me that they never go to 100% GDI because, once turned off, upon coming back on the first one or two PFI injections just wet the port and valve so you go lean for a couple of cycles.

Its like 75-80% DI for 25-30 seconds on a cold start. Winter temps changes things slightly.



I dont think Ford would have added DI other wise. They didnt keep it in the GT500's.

What does the Mustang GTD 5.2's have?

 

[engineermike]

What does the Mustang GTD 5.2's have?

Almost certain it's PFI only. There is no HPFP on either valve cover.

 

[WildHorse]

Anywhooooooo got my answer.
+2° for the whole RPM range. Monitor knock, all good.

 

[K4fxd]

+2° for the whole RPM range. Monitor knock, all good.

It seems Mikes's chart is correct.

 

[WildHorse]

t seems Mikes's chart is correct.

The KS's are still adding ... so there's that.

 

[K4fxd]

The KS's are still adding ... so there's that.

Now the next question is how much timing is too much? Did Ford actually test MBT and fill the tables or did they just guess?

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