My “Real Gas” Experiment

[pgandw]

Originally Posted by HiTech

Please never, ever, ever run 85 octane in an engine recommending 87. There is significant risk of dangerous preignition.

I did buy a 2001 E450 v10 that I drove for 10 years. My recollection is I got about 9.5 MPG long term not towing, no matter what the conditions. However, that was running a 20 year old PCM, strategy and calibration. These are periodically updated with significant new algorithms and technology (faster processors with much better knock detection, for example). I believe the V10 had one hardware update sometime since then as well, before Godzilla replaced them.

One of the byproducts of faster PCMs is the ability to be much more aggressive on adding a bunch of timing, say to climb a hill, and then let the heads cool off on the following downhill run. Modern Ford HP and torque numbers are based on top tier premium fuel, a recent change. The reason is that premium gives you more power and torque on modern Ford engines.

MOST of the time, an engine does not need the full rated octane. 85 octane gas is sold at higher altitudes for precisely this reason. At altitude, a normally aspirated engine cannot generate the pressures needed to cause pre-ignition, so a lesser octane gas can be safely used. A turbo or super charged engine maintains internal pressures and temps at altitudes, so running lower octane is not advisable.

The full octane rating is needed to prevent pre-ignition when heavily loaded and/or running hot (the "normal" when towing). That's when internal pressures and temps are at their highest, and pre-ignition is most likely. Cruising with light loads doesn't generate high pressure or temp, and so lower octane is suitable.

Since I live at 6700ft and seldom go below 5000ft, running 85 octane for normal driving has no detrimental effects on my non-turbo engines. When I'm towing, I specifically use 87 octane at altitude, and 89 octane at sea level so that I do not trigger timing retardation.

Ford does rate their turbo engines using 93 octane gas. Which tells me that if I need max power or am running the engine hot, I need to be using 93 octane. Cruising and not using much power, I can probably use a lower octane gas safely.

Learned all about octane, pre-ignition, engine temps, timing, and mixture flying carbureted piston engine aircraft.

Fred W
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[Matthuck88]

Originally Posted by rsdata

I often travel 265 miles from N. KY to the Cleveland area, up I-71. I have a 32 gallon tank then when it reads empty will only take 27 gals of gas. I have experimented with different blends and different speeds at different times of the year. I calculate mileage manually. I have observed variations between 21.5 to 18.0 MPG

There appears to me, to be un-observable and un-measurable variations in a number of variables during the these trips that account for this variation.

There is a reason why salt-flat speed runs have to be dome in both directions within a short time frame... to minimize outside factors.

My burning question is where do you find 89% non-ethanol gas for only 30 cents per gallon more then E-10 87 octane?

I don't see any Wawa stations until I hit FL, and E-0 gas her in OH and KY are only sold at marinas for the most part.

We have wawa’s like weeds in eastern PA, I think they started here 30+ years ago. One near me has 89 ethanol free for about $.60 more than 87 blend. I was going to use in my truck last weekend to run to the mountains but decided against it.

[Beachbourbon]

MPG calcs for towing and RVing are a fool's errand

[TitanMike]

Originally Posted by Beachbourbon

MPG calcs for towing and RVing are a fool's errand

Agree, mileage is what it is, but some of it can be controlled.

I glance regularly at ma Scangauge II and will adjust speed for higher numbers when i can.

When fighting a headwind I can see noticeable gains when slowing down. Tailwinds allow me to go faster without sacrificing mileage.

Beyond that, it is what it is.

[nomad297]

Originally Posted by Matthuck88

We have wawa’s like weeds in eastern PA, I think they started here 30+ years ago. One near me has 89 ethanol free for about $.60 more than 87 blend. I was going to use in my truck last weekend to run to the mountains but decided against it.

The WAWA I went to was in south eastern PA, south west of Philadelphia. Regular 87 octane was 2.699 per gallon and the non-ethanol 89 octane was 3.009 per gallon. I still would have tried it out if it was $.60 per gallon more.

Bruce