Which octane for new Ford V-10

[RRTom]

The manual says 87, but for better performance (hot weather, towing) use 91 OR HIGHER. Just wondering what the real world experience has been. The dealer gave us a full tank, but you know he put 87 in it to save a few dollars.

[Chum_lee]

FloridaRosebud wrote:

T18skyguy wrote:
The gas companies adjust octane for the localities they serve. When they can use lower octane it saves them refining costs. You will see lower octane in the high country like Moab, Utah, which is at roughly 4000 feet. At that elevation the air is thinner, and the compression ratio lower as a result,(that's why we complain about power up high) so they cheap out on the gas. You can run 85 octane all day on level ground in cool weather with no problems, but when you go to climb the Grapevine it might be different. There are so many factors; engine condition, temperature, pressure, load, it can be real hard to pin it down to one situation

Um, the compression ratio has nothing to do with elevation. That's a mechanical ratio of of cylinder volume at full stroke vs cylinder volume at top dead center. The reason you loose power is the O2 is less at elevation, messing up your mixture ratio.


Al

Not completely true. At sea level and standard air pressure, the engine sees +-14.7 lbs/sq. in manifold pressure at full throttle. With 10:1 compression, the maximum theoretical compression would be 147.0 lbs. At elevation, a naturally aspirated engine starts with less static pressure so the overall compression pressure is less. Do the math. That's how the oil companies get away with lower octane fuel at altitude. That's why your naturally aspirated engine cannot generate as much power at elevation. It is true that there is less O2 available but the concentration of the inert part of the air (N2) effects things too.

The static compression ratio doesn't change, but, the max. cylinder pressure the engine can generate does. The maximum cylinder pressure is directly related to the power/torque the engine can generate.

Chum lee

[T18skyguy]

At sea level, the oxygen is 20.9 %, at 4000 feet it's 17.9 % so yes there's an effect for sure,but the primary issue is decreased pressure. Turbochargers make up for that, but they don't push more oxygen,that percentage remains the same.

[FloridaRosebud]

T18skyguy wrote:
The gas companies adjust octane for the localities they serve. When they can use lower octane it saves them refining costs. You will see lower octane in the high country like Moab, Utah, which is at roughly 4000 feet. At that elevation the air is thinner, and the compression ratio lower as a result,(that's why we complain about power up high) so they cheap out on the gas. You can run 85 octane all day on level ground in cool weather with no problems, but when you go to climb the Grapevine it might be different. There are so many factors; engine condition, temperature, pressure, load, it can be real hard to pin it down to one situation

Um, the compression ratio has nothing to do with elevation. That's a mechanical ratio of of cylinder volume at full stroke vs cylinder volume at top dead center. The reason you loose power is the O2 is less at elevation, messing up your mixture ratio.

Al

[T18skyguy]

The gas companies adjust octane for the localities they serve. When they can use lower octane it saves them refining costs. You will see lower octane in the high country like Moab, Utah, which is at roughly 4000 feet. At that elevation the air is thinner, and the compression ratio lower as a result,(that's why we complain about power up high) so they cheap out on the gas. You can run 85 octane all day on level ground in cool weather with no problems, but when you go to climb the Grapevine it might be different. There are so many factors; engine condition, temperature, pressure, load, it can be real hard to pin it down to one situation

[dodge_guy]

lonewolf80 wrote:
Count me in with the waste of money crowd going above the recommended 87 octane. My guess would be the only gas that would improve performance and mpg would be ethanol free gas which is usually between 91-93 octane, but costs .30-.40 more per gallon.

I filled up with that and n northern WI and did it make a difference! Felt like the engine had another 40HP!!! I’ll always go ethanol free if available even with the cost difference.

[lonewolf80]

Count me in with the waste of money crowd going above the recommended 87 octane. My guess would be the only gas that would improve performance and mpg would be ethanol free gas which is usually between 91-93 octane, but costs .30-.40 more per gallon.

[FIRE_UP]

I just got to this thread.
Our previous coach, a '99 Fleetwood Bounder 34V with the Triton V-10 (275HP version) and F-53 chassis, normally was fed 87 octane due to where we live in So CAL at the time of use. But, when we went on a trip from San Diego to Moab UT for an Easter Jeep Safari one time, I stopped for fuel in UT and just started pumping what I thought was 87 octane.

I wondered why the price was so low compared to CA (other than the normal price that's lower than CA). When I looked at the pump and what I was pumping, it was 85 OCTANE!!!!!!!! I immediately stopped pumping but, had already put over 20 gallons in. (the pump was fast) Anyway, since I'd put that much in it already, I figured what the heck, just keep going. So, I filled it with 85. The tank had about 1/4 in it when I started filling it.

So, off we went. In the ensuing miles, I noticed absolutely ZERO difference in any phase of engine operation. NO pinging, no loss of power, no temp differences, no starting problems, NOTHING. So, guess what, I also ran that 85 octane in our Jeep when we got to Moab. We were there for a week so, without a doubt, as many runs as we went on and the amount of times I'd re-filled the Jeep, it was no doubt, running on pure 85 after a bit.

It to showed zero signs of issues by running on that 85. So, after that, each time we went to Moab from San Diego, I'd fill the coach and Jeep with 85 and never looked back. It worked, plain and simple.
Scott

[T18skyguy]

The history of Octane boosting is interesting. What I read was that researcher's discovered that lead was ideal for this purpose as World War 2 started. They quickly added it to the fuel for the Merlin engine for the P51 Mustang. The lead ensured it's performance advantage over the Japanese Zero. They kept it a closely held secret during the war.

[jerseyjim]

Very first time I've heard of this....my V-10 (2001) runs 87 since day 1, tows a "toad" 80% of the time....58,000 miles.

If any "pinging" at all, the computer shuts it down immediately. Did it ever happen? have no idea. Never noticed any drop in power. Of course, I've never climbed the Rockies, but AZ has some neat hills......

[timmac]

Thanks for that post T18skyguy,
Yea my motorhome does have 46,000 miles plus I tow 6500lbs so maybe that combo is my issue, I need to change the factory plugs soon maybe this would help but for now my RV runs better with 89 octane and no pinging.


When I was using 87 octane the pinging was very little but mostly when climbing the large hills.

[T18skyguy]

Octane requirements increase as a vehicle ages. This is from burnt fuel deposits on top of the piston and combustion chamber(like spark plug deposits). With a smaller physical volume, and the piston pushing the same amount of air, it raises the compression ratio. Engineers call it "Octane creep". The process starts right away, but starts to be noticeable at about 30-40 thousand miles. That's why they almost never ping when their new. So, if you start with a compression ratio of 8.5, after a couple years it's higher than that and 87 octane fuel just doesn't cut it any more, and you need 89 octane. Add the extra load of an RV plus heat and you get problems. If it gets bad enough, you blow the engine with a broken rod or such. Pre-ignition can be a problem before you ever hear it. I have seen it on an oscilloscope, but that's another story. With aircraft we run 100 octane. No pre-ignition can be tolerated, else a cylinder blows off. My new rig is fine right now with 87, but I'll up it when it asks for it and probably be at 91 at some point. When someone blows an engine at 25-40 thousand, they get blamed for not changing the oil or some other neglect, when it's the fuel that's responsible all along.

[Ralph_Cramden]

Chum lee wrote:
chances are you won't be able to tell the difference between 87 and 91.

Your wallet will know the difference.

[T18skyguy]

Dennis12 wrote:
The manufacturer tells you this because they have tested it. I have a V10. I have run 87 octane and i have run 106 octane from a local airport. Same fuel mileage. See no difference in power or anything else.

What Dennis !! You mean you snuck a tank of 106 low lead in your rig? Watch out the feds don't get you 🙂 (only kidding)

[timmac]

Dennis12 wrote:
The manufacturer tells you this because they have tested it. I have a V10. I have run 87 octane and i have run 106 octane from a local airport. Same fuel mileage. See no difference in power or anything else.

Yes many times this is true, but if performance upgrades are made sometimes a little higher octane works better like in my case..