87 vs 93 Octane

[Gros Ventre]

The intake valves can indeed be left open longer.


semi related question, we all know ford doesn't recommend E85 or even 10% 85 in Ecoboost engines. What is the actual tested lower limit of what the antiknock mechanisms can account for?

Leaving the intake valves open longer is the mechanism that Ford used to create the pseudo Atkinson cycle in the Escape Hybrid. What that does is allows th compression stroke to push some of the air charge back out. Effectively this reduces the cylinder charge by reducing the pressure in the cylinder on beginning compression... This improves MPG but reduces power ouput of the engine.

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[Gros Ventre]

And yet there's still a harmony in the universe that we both exist in simultaneously.

I remain amazed that the entire issue of Gasoline Direct Injection is ignored in this discussion. Many woud call it heresy to say this, but in a real sense, GDI makes this more like a diesel engine (perish the thought). This is since the engine doesn't have to care about detonation since it is designed for it on fuel charge injection. The whole rationale for an Octane rating is resistance to detonation during compression... Funny thing about that GDI, it nearly makes an octane rating irrelevant...

 

[Snakebitten]

Even with direct injection, if you just finished a tank of 93, and you filled with 87, watch those knock sensors complain!

After just a few seconds of knock, the OAR adjusts, and a different timing table becomes the strategy.

Knock some more, and it lowers OAR again, thus another base timing table.

Direct injection on the 3.5 Ecoboost doesn't seem to lead to octane agnostic.

I'm just saying

 

[Gros Ventre]

Even with direct injection, if you just finished a tank of 93, and you filled with 87, watch those knock sensors complain!

After just a few seconds of knock, the OAR adjusts, and a different timing table becomes the strategy.

Knock some more, and it lowers OAR again, thus another base timing table.

Direct injection on the 3.5 Ecoboost doesn't seem to lead to octane agnostic.

I'm just saying

OK... So why did Ford split for the complexity and cost of the GDI? If it doesn't convey some kind of advantage in the thermodynamic cycle what good is it? And don't forget that it added a problem that they had to fix by bringing back the intake valve fuel injection just to keep the intake valves clean(er). I'm just sayin'.

 

[Snakebitten]

I don't think anyone is trying to make a case that Direct Injection doesn't have many advantages. It certainly does. But I don't see how it takes pre-detonation off the table.
Knock still exists with GDI.

 

[Gros Ventre]

I don't think anyone is trying to make a case that Direct Injection doesn't have many advantages. It certainly does. But I don't see how it takes pre-detonation off the table.
Knock still exists with GDI.

Hey, if there's virtually no fuel in the cylinder during the compression stroke... where's the detonation?

 

[Samson16]

The 3.5 has direct and port injection correct? Are the port injectors only used sparingly to keep the backside of the valves clean or what? Direct injection certainly gives far more control of the air/fuel ratio but you can only lean out a motor so much. We want ecoboost not ecoboom.

Or are you saying the piston compresses air and then the fuel injector sprays fuel somehow into the tiny highly pressurized cavity at the top of the stroke just before spark?

I found what we need to get the answers we seek.

https://www.ebay.com/itm/275955934590?hash=item404041657e:g:BQkAAOSw~MNkk3wx

 

[SilverPigeon]

Alright, there is far too much opinion and talk of other engines which is confusing the subject at hand (Caps Locked words are emphasis, not shouting ?).

1. This entire thread discussion should only be about the 5.0L, as referred to in the title.

2. Some people seem to be getting confused about the flex fuel nature of this engine. Indeed it is capable up to E85 (over 100 of your octane, we use RON exclusively over the ditch). It's when you start to put lower octane in it that the timing is retarded and one LOSES power; nothing is GAINED past what the tables already say when one uses higher octane fuel. Therefore, as an example, putting e100 into a stock 5.0 does nothing for performance. That requires a tune (modified tables) and an upgraded fuel delivery system.

3. It is extremely hazardous for the health of the engine to put any lower octane in it than 87. At 12:1 compression, the high cylinder pressure cannot help but start to detonate the low-octane fuel because there is a limit to how far it can retard timing and, at this point, regardless of wether PFI or DI or BOTH (the case at times) are in use, the ECU MUST spray SOME fuel into the cylinders to keep the engine running.

4. Why do 5.0 mustangs make more power and less torque than 5.0 f-150s? Same engine, EXCEPT (importantly) for the cams! Most significantly, the intake lobe profiles are modified in the f-150 5.0 to allow for a shorter intake valve open time and therefore a smaller window for the ECU to spray fuel. This results in a smaller volume of fuel entering during the intake stroke and being compressed during that following compression stroke. In other words, it is INTENTIONALLY running slightly LEAN compared to a mustang until further up the rev range. The resulting trade-off is more torque lower down, but less power higher up. This is why an f-150 5.0 can lug well, especially on the higher octane fuels. Think towing 12,000 lbs.; not good for a mustang ? This whole point is the main reason that, for an f-150, higher octane is better for towing etc. and why lower octanes are so dangerous in an f-150 5.0.

5. Why do supercharged 5.0 configurations require 93 octane minimum? The increased volume of air-fuel mix, provided by the bigger injector/forced air (always in a blower kit) being compressed... higher cylinder pressure has the same effect upon detonation that running lean at relatively lower pressure does. Bad economy if one goes WOT as more air means more fuel, but that richer mix and advanced timing commanded by the supercharged tune , and made possible by the higher octane, makes for less possible detonation. It's why for maximum torque/power scenarios, e100 is used (after upgrading the fuel delivery system of course).

Detonation occurs predominantly in LEAN, low octane scenarios. The above are FACTS. Facts dont care about opinions. If the above contain errors of fact, I'll gladly accept correction IF the evidence demands it. Otherwise, I'll take the documented evidence of my statements of fact because it's out there. If one doesn't believe the facts, it's not my problem, science says "show me the evidence to remove my scepticism and change the way we understand things to work".

 

[Gros Ventre]

The basics of the engine thermodynamic cycle are that the Compression ratio and thus the peak cylinder pressure determines the required octane. Then how much energy can be extracted from the fuel flows from that. Putting in higher octane than designed does not increase power. Don't confuse jamming more fuel in a cylinder with changing the engine basics.

 

[SilverPigeon]

Are the port injectors only used sparingly to keep the backside of the valves clean or what?

Definitely Or what ?

the following screenshot is taken from this article: https://www.enginelabs.com/engine-tech/efi/how-does-dual-fuel-work-on-a-gen-3-coyote/

yes, it is coyote not EcoBoost, but as you say, the EcoBoost is a pi-di engine, and similar tables MUST exist for it ?

 

[SilverPigeon]

The basics of the engine thermodynamic cycle are that the Compression ratio and thus the peak cylinder pressure determines the required octane. Then how much energy can be extracted from the fuel flows from that. Putting in higher octane than designed does not increase power. Don't confuse jamming more fuel in a cylinder with changing the engine basics.

If you're writing to me, you've misunderstood my words. I said exactly what you are saying in all but your last sentence, only in different words.

 

[Gros Ventre]

The 3.5 has direct and port injection correct? Are the port injectors only used sparingly to keep the backside of the valves clean or what? Direct injection certainly gives far more control of the air/fuel ratio but you can only lean out a motor so much. We want ecoboost not ecoboom.

Or are you saying the piston compresses air and then the fuel injector sprays fuel somehow into the tiny highly pressurized cavity at the top of the stroke just before spark?

I found what we need to get the answers we seek.

https://www.ebay.com/itm/275955934590?hash=item404041657e:g:BQkAAOSw~MNkk3wx

Info I have read from Ford says that the port injectors are there only to keep the valves clean and that they at most contribute 10% of fuel flow into the cylinder. Yes, the direct injectors are capable of injecting fuel at peak cylinder pressure. When someone in this discussion answers how these direct injectors are in fact used in the cylinders we will have an answer. It just doesn't make sense that Ford would go to the expense and complexity of the GDI, followed by adding the port injectors to keep valves clean, unless they were using it to change the thermodynamic cycle inherent in the engine.

 

[Gros Ventre]

If you're writing to me, you've misunderstood my words. I said exactly what you are saying in all but your last sentence, only in different words.

K, no sweat...

 

[SilverPigeon]

For everyone's info, I am also saying things that all "sides" of this discussion are saying. My words are extremely carefully chosen to remove disambiguation.

 

[SilverPigeon]

Info I have read from Ford says that the port injectors are there only to keep the valves clean and that they at most contribute 10% of fuel flow into the cylinder. Yes, the direct injectors are capable of injecting fuel at peak cylinder pressure. When someone in this discussion answers how these direct injectors are in fact used in the cylinders we will have an answer. It just doesn't make sense that Ford would go to the expense and complexity of the GDI, followed by adding the port injectors to keep valves clean, unless they were using it to change the thermodynamic cycle inherent in the engine.

Look at the pi-di tables a few comments above and you have the answer to that question. The information that you read regarding port injectors was wrong, or the interpretation of it was incorrect.

Everyone, look closely at the warm pi-di table, there are two very important points here:
1. If you go ¾ throttle from idle, 80% of your fuel is coming from PORT injection.
2. Over the entire table, there is NEVER any less than 10% Port injection.

There are many things we can glean from this. Some are:
1. An intake stroke will ALWAYS have some fuel present for the compression stroke. 10% is NOT an insignificant amount.
2. Your best intake valve/port cleaning happens at low revs, low load. Your 10R80 will let you do this.
3. At HIGH load (WOT, towing etc.), the 5.0 di system does not provide all necessary fuel to make the torque demanded at that time. We then get a LEAN mix of port-injected fuel being compressed before the di finally serves us a charge. It's that lean situation which makes anything lower than 87 too difficult for the PCM to retard.

Upshot: if you want to lug around town, or tow heavy, or go ¾ WOT to get to the next red light, your fuel economy will SUCK, but your intakes will be clean ?

oh, I'm NEVER putting anything less than 98 RON (your equivalent to the needlessly complex (RON+MON)/2 of 93) in my baby. ?

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