87 to 93 octane

[mikey1988]

this may be a weird question but for those of you with a 5.0L did you notice your kms to empty on the dash goes way higher when you fill up with 93 octane compared to 87 octane? is there a sensor of some kind in the fuel tank to tell what fuel is being used? with 87 in my rcsb 5.0L the distance to empty is around 580-610 kms when i use 93 the distance to empty is 740-770 kms and the truck has a lot more power almost like a very mild tune

now my rcsb 5.0L also has a cold air intake and borla atak exhaust but thats all the performance mods i have done not sure if those would make a huge difference

Sponsored

 

[Buyer2021]

is there a sensor of some kind in the fuel tank to tell what fuel is being used?

No.

At this time there is no sensor technology which provides a direct real-time measurement of fuel octane value.

Remember, a fuel's octane number value is simply a laboratory-test derived expression for propensity to 'detonation' at a given set of standard conditions.

The only way a vehicle 'infers' different octane is from it's 'knock-sensors' and associated PCM logic. The PCM, acting at a rate of many times per second, constantly tries to advance ignition timing and other parameters until it senses the early onset of 'detonation' (usually far below the operator's threshold of detection) and limit's those parameters affecting the combustion process at that point.

The vehicle never knows the 'octane number', it just knows how much it can tweak it's dynamic tune for a given fuel and other conditions without causing damaging detonation. All other things being equal a higher octane fuel will therefore deliver more 'effective power' for a given set of conditions.

In simplistic terms higher octane allows more ignition timing advance without engine damage; but in modern engines with variable valve-timing and variable fuel-injection rate and timing, there's more in-play than just ignition timing.

 

[Francis Bellows]

exactly like said above. The 93 octane makes more power per stroke due to how Ford set these trucks up. More power means that for a lot of your time driving you may use less throttle than with 87, which in the end uses less fuel and gives you higher range. Is it worth the extra cost? That’s up to you. I only run 93 octane and couldn’t care less about the extra few dollars per tank!

 

[Blueshound]

Regardless of the Lie-O-Meter (LOM) 93 does give better performance and one or two extra mpg with the 5.0. Not as much as the LOM thinks though. The only way to know for sure is calculate actual miles and gallons. For me it will get 17-18 mpg on 87, and 19-20 mpg on 93. Around here it's almost an extra dollar a gallon for premium, so the extra performance not worth it to me.

 

[Gros Ventre]

Interesting. Had not thought Ford would set up the programming to enable use of higher octane fuel. Effectively this turns the engine into a high compression engine.

 

[KBKEITH]

Running 93 makes a noticeable difference in performance and MPG, especially it seems in the 2.7 and 3.5 due to timing and boost.

I watched an interview a few years ago where one of the lead engineers for the 2.7 commented that using 93 would bump HP by 20. Can’t recall the increase in TQ.

 

[Chease44]

I use 91 in my 3.5 EB pretty much all of the time. I find it does get better mileage on premium which might just be due to no ethanol in the 91 where I fill up. I have figured it out a bunch of times over the last couple trucks and usually the cost per 100km works out to a wash, but I am ok with that as it does seem like the truck runs smoother on 91 and it is recommended for towing anyways.

 

[RuggedGoods]

The only way a vehicle 'infers' different octane is from it's 'knock-sensors' and associated PCM logic. The PCM, acting at a rate of many times per second, constantly tries to advance ignition timing and other parameters until it senses the early onset of 'detonation' (usually far below the operator's threshold of detection) and limit's those parameters affecting the combustion process at that point.

The vehicle never knows the 'octane number', it just knows how much it can tweak it's dynamic tune for a given fuel and other conditions without causing damaging detonation. All other things being equal a higher octane fuel will therefore deliver more 'effective power' for a given set of conditions.

In simplistic terms higher octane allows more ignition timing advance without engine damage; but in modern engines with variable valve-timing and variable fuel-injection rate and timing, there's more in-play than just ignition timing.

Terrific explanation. You in the industry? I gotta go check on my running dyno tests.

 

[RuggedGoods]

Running 93 makes a noticeable difference in performance and MPG, especially it seems in the 2.7 and 3.5 due to timing and boost.

I watched an interview a few years ago where one of the lead engineers for the 2.7 commented that using 93 would bump HP by 20. Can’t recall the increase in TQ.

My wife drives a Mazda CX-9 with their 2.5L turbo. It's rated at 222 HP on 87 octane, and 250 on 91/93. We run 87 because she rarely pushes the pedal to the floor. I'd love to pick up a JB4 for it and run 93 if it were my daily....

 

[Buyer2021]

Interesting. Had not thought Ford would set up the programming to enable use of higher octane fuel.

I can't think of a single modern engine from any manufacturer that doesn't employ at least variable ignition timing and 'knock sensors' to accommodate some degree of different octane and other factors relating to combustion (and thereby to at least some small degree the engine's effective power output). More sophisticated engines (e.g. EcoBoost, among many) can better 'optimize' higher octane fuel power-delivery, but that has it's limits, too.

Most 'current' engines have PCM logic and associated variable parameters affecting combustion which is effective from a lower octane value of ~85, with the ability to 'optimize output' petering out above an octane of ~97 (the octane range of common pump-gasolines in the US).

In any case it's always important to respect manufacturer minimum octane recommendations to avoid detonation-related engine damage in certain conditions (e.g. under severe load, at higher altitudes, etc). You can always safely run higher-than-minimum-recommended octane, you just may not enjoy any power-delivery benefit and you almost certainly won't enjoy any 'economic payback'.

 

[Gros Ventre]

Well, thank you... My 92 Suburban has those and they are important for protection of the engine. So I'm aware of such things. That is different from enabling what amounts to enabling an engine to function as a "high compression" engine... Such a software design is far more complicated for engine management since in addition to protection by retarding spark it advances spark to enable "high compression" when the basic engine was not set up as "high compression."

 

[diambo4life]

I can't think of a single modern engine from any manufacturer that doesn't employ at least variable ignition timing and 'knock sensors' to accommodate some degree of different octane and other factors relating to combustion (and thereby to at least some small degree the engine's effective power output). More sophisticated engines (e.g. EcoBoost, among many) can better 'optimize' higher octane fuel power-delivery, but that has it's limits, too.

Most 'current' engines have PCM logic and associated variable parameters affecting combustion which is effective from a lower octane value of ~85, with the ability to 'optimize output' petering out above an octane of ~97 (the octane range of common pump-gasolines in the US).

In any case it's always important to respect manufacturer minimum octane recommendations to avoid detonation-related engine damage in certain conditions (e.g. under severe load, at higher altitudes, etc). You can always safely run higher-than-minimum-recommended octane, you just may not enjoy any power-delivery benefit and you almost certainly won't enjoy any 'economic payback'.

Yup.....my old ass 91 Mitsubishi Galant VR4 employs similar logic. Now, I tune it myself and it has a logic programmed in it to *always* use the "high octane" maps for fuel/timing advance and not blend between them depending on knock activity.

 

[Buyer2021]

Well, thank you... My 92 Suburban has those and they are important for protection of the engine. So I'm aware of such things. That is different from enabling what amounts to enabling an engine to function as a "high compression" engine... Such a software design is far more complicated for engine management since in addition to protection by retarding spark it advances spark to enable "high compression" when the basic engine was not set up as "high compression."

There's only two ways to effect 'variable compression' in an engine:

• Altering valve timing (specifically overlap between intake and exhaust)
• Altering boost with turbo/super charging and associated BOV

Most engines with those mechanical features have a necessarily more sophisticated PCM than those without those features. Some with turbo/super charging even employ electronic variable BOV control rather than a BOV with a fixed-pressure boost bypass point.

Yeah, engine controls on modern engines can be very 'complicated' when there are so many variable parameters in play. Obviously OE manufacturers expend tremendous time and talented effort in determining how to optimize all these many factors while providing engine longevity for every operating condition likely to be encountered by consumers at large.

IMO some (perhaps most) folks inclined to modification in search of increased power don't realize how risky it can be or the long-term consequences of messing with the delicate balance of the many variables involved. It's all a balance of compromises.

 

[Gros Ventre]

I don't need your tutorials, thank you very much...

 

[Buyer2021]

I don't need your tutorials, thank you very much...

I apologize if offense was taken, certainly none was intended.

Sponsored