Don't let this turn into another octane thread...

[Grimmer]

I have a specific question related to octane, but don't want to start yet another octane thread... Here goes, let's see what we can get:

I'm Looking at the Ford Performance Racing Power Pack 2. All of the FPR tunes require the use of 91 octane minimum (instead of the published 87 octane minimum). In my locale we are at about 4,700 feet above sea level. The common gasoline options are: 85, 89, 91 and 88 ethanol free. There is also one station in town that pumps 91 octane ethanol free but at nearly double the cost ($4.00+ vs $2.30 for reference).

My previous car took a 20% loss of fuel economy when the "up to" 10% ethanol was added to all the fuel around here. Hence my desire to use the ethanol free option (if possible). It is commonly held that high altitude effectively lowers the octane requirement a bit (although there is a specific CYA style warning against this in the owner's manual).

So here's the question: Is 4,700 feet of altitude enough to allow running the 88 octane ethanol free in a canned tune that requires 91 octane at sea level?

I suspect the drop from 91 to 88 (3 octane lower) is too great since the common blends around here are only 2 octane lower (85 vs 87, 91 vs 93); however, it is only different by 1...

Any thoughts?

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[NoVaGT]

I ONLY USE 93 OCTANE!!!! IF YOU DON'T USE 93 OCTANE YOU'RE A MORON!!!! ONLY I KNOW WHAT I'M TALKING ABOUT EVERYONE ELSE IS WRONG!!!!



That felt good......

Now, OP, what was the question???

 

[whalesalad]

I'd probably avoid a canned tune in your situation. If your altitude requires a different octane then I'd find a tuner who has experience with that situation.

Or blow the hell out of it and the altitude difference won't matter so much

 

[SpeedLu]

If the tune calls for 91, fill up with 91. Don't overthink it.

 

[ShelbyGT350]

My local independent station has unleaded 87, 95 and 100 octane gas (Sunoco brand). Hopefully I won't blow my engine with the high-octane stuff! FYI, the latter 2 grades are $7.50 and $8.50/gallon!

 

[markmurfie]

It's all about the stoichiometric value of the fuel. The stock ECU is based off 14.08 which is the value for E10. Then it works in lambda so no matter what fuel you run it thinks it e10 and will run the same volume. If you use e85 it runs to lean and is bad for the engine. With out changing to the 14.7 stoich value of pure gasoline I don't think you will gain MPGs. In fact it will run rich and you may lose MPG.

I think you should look into a flex fuel tune so that no matter the fuel you get it's full benefit. Make sure your tuner knows you will be running pure gasoline.

Yes for best fuel mileage use pure gasoline.

 

[jasonstang]

So, this is how I am looking at it.
At sea level, air pressure is roughly 14.7psi, given engine compression of 11:1, at greatest pressure is gonna be 162psi. Say anything higher than that will cause knocking.
At 4700ft, the air pressure is about 12.4psi, so with 11:1 compression ratio, you are looking at 136.4psi.
Now we bring the max high altitude psi to sea level to calculate the relative compression ratio 136.4:14.7 = 9.3:1.
The engine will always try to inject the right amount of gas given air volume from the MAF. Assuming the tune is premium gas only at sea level, you engine is effectively working as 9.3:1 compression ratio at sea level which should be fine with 88 octane at your altitude.

 

[WhiteyDog]

I ONLY USE 93 OCTANE!!!! IF YOU DON'T USE 93 OCTANE YOU'RE A MORON!!!! ONLY I KNOW WHAT I'M TALKING ABOUT EVERYONE ELSE IS WRONG!!!!



That felt good......

Now, OP, what was the question???

:lol::lol::lol::lol: :lol::lol:

 

[GTBOB]

I run half a tank of diesel with 1 gallon of Seafoam/1 gallon of Roundup weed and grass killer for the past year. Runs fine at any altitude. Hasn't been a recorded case of bed bugs in my township since.

 

[18psi]

My car on a Lund FF tune knocked from 5k to redline on CA 91oct. Lund pulled out timing, and it still knocked. I tried different stations, and it still knocked. I added a couple gallons of e85 and poof knock disappeared. Sometimes even 91 is not enough.

He said if he was to take away any more timing, it wouldn't even make any power over the factory tune.

The point is, if you want power you need octane for knock suppression. Otherwise you either don't make any more power, or risk damage to your engine. Playing science lab with your car is probably not going to result in anything good either. This is also another reason why I think it's insane not to have the ability to monitor/log your car's health with some of these "tuning solutions".

 

[Grimmer]

It's all about the stoichiometric value of the fuel. The stock ECU is based off 14.08 which is the value for E10. Then it works in lambda so no matter what fuel you run it thinks it e10 and will run the same volume.

I have recently tried running the E0 gas. Although my "data set" is not very big yet, it appears early on that I will not get any additional fuel economy as you mentioned. It seems that running the more expensive E0-88 is not likely to get me any gains over the E10-91 like it did in my previous car (which was likely setup/tuned for the E0).

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