engineermike

You said this, but then later say that it's only certain conditions where you would gain power with premium. If you gain power with premium fuel, the you were clearly running in detonation with 87. That, to me, is running the ragged edge of detonation.

Same as above. . . if in hot weather or heavy towing you gain power with 93, then you were having detonation on 87. That is the ragged edge.

I get what you're saying. . . that the EB makes the same power on 87 as 93 in ideal conditions, but in hot weather the 93 makes more (meaning it was detonating on 87 - after all, why else would an engine make more power on 93?). However, I contend that if BD can gain 40 hp and 50 ft-lb on 87 with more timing and/or boost, then it clearly wasn't running that close to detonation to begin with.

Viin

You are assuming the ECUs map allows the engine to get near detonation. Is it possible that the ECU map is very conservative and retarding timing in what it considers "less than ideal" conditions before detonation even occurs?

The programming packs may override this, allowing the engine to keep proper timing.

At 10.5:1 AFR, I find it hard to believe detonation is even possible.

69428SCJ

The first reference was in regards to the 6.2 that is rated on premium. Clearly it makes less HP on 87...when and where who knows.

The EB is the one that can make more or really remain as rated on 93 if the conditions fall out of the 87 tuning parameters. That's my guess anyway.

I'm guessing BD doesn't care about adding a little boost on the high end where the factory programming drops boost. They sure don't care about how they make the tranny shift. I'm wondering if their programming allows for 40HP all the time or if they are utilizing the knock sensors when conditions dictate. I have still not seen anything in writing from BD saying their tune is an 87 octane tune...just a lot of hearsay from people who have talked to them. I'll take that with a grain of salt. A little detonation never hurt anything. I would not consider it the ragged edge. What's your take on Ford recommending premium in the other EB 3.5 applications?

engineermike

If that were the case, using different octane would make no difference at all.

69428SCJ

I'm guessing that's what BD figured as well...and kept a little boost in there with that 10.5:1. That is a lot of fuel!

engineermike

I'm purely guessing based on my experience with large companies. . . they may recommend that just to give them some extra safety factor. It doesn't cost Ford anything, but it does give them some more padding. The OEM's benefit/cost ratio for that recommendation is infinite!

Viin

Good point. I can't think of how the ECU/ECM would know to retard timing without detecting knock unless they have maps based on intake air temps or something ..

TruckLarry

Well, I guarantee you my '07 edge 3.5 did better, in the summer, on 93 by 2-3 mpg highway.

I run 87 in the winter and 93 in the summer. My EB definitely runs Better on 93, but only in the summer.

p38fln

I saw the same thing - better MPG on premium, but more of a difference in the summer months.
I got it up to 22.5 MPG in the summer running premium at 65 MPH, something I haven't managed to repeat since.

It's a DI engine - you'd think predetonation should be next to impossible if it was set up properly. No fuel in the cylinder until its ready for it... although it probably isn't as precise as a diesel with the timing, maybe they have to spray some in before its time to ignite it. I know there can be multiple injection "events" per compression stroke per cylinder.