I have a 06 FX4 with a 5.4. Finally approaching 100k on it soon. Truck has a airaid jr intake, which is essentially like the GOTS mod. Other than that, its completely stock. I'm interested in taking advantage of 90 octane pure gas as there is a station in my town. I'm curious if I can use 90 octane in my stock engine safely? Obviously I know I can tune it for specific octane, but didn't' know if the computer can regulate the A/T where the motor would run ok with it.

 

Sure you can use it. You just won't get the best mpg return from using it. Ideal you want to use the lowest octane before pre combustion occurs.

The higher the octane number the slower the combustion in the cylinder.

 

If the other choice has 10% ethanol, I would think he would get better mpg with the straight gas. You lose close to 10% efficiency with the ethanol.

 

True I never considered that.

 

90octane.
That "super"
I always run 87(regular) in my 5,4 07 and no issue.

 

I have tried 91 octane pure gas in mine, and didn't get any better mileage or performance. It didn't hurt anything either.

 

Safe? It only needs 87, so it's beyond safe! But yeah, I'd at least try it out. If for no other reason, support the pure gas any way you can.

 

Won't hurt, or help. Will cost more.

I've run tests with my truck ('06 4x4 SCAB with 4.6) and programmer (Gryphon) using 10% ethanol blend versus pure gas. I ran both tests on 87, then 93 octane (tuned for octane). Tests were done on highway, then mixed driving. Three tanks of fuel for each test, over the course of two months.

After several thousand miles of testing, the results were; no difference in mileage between pure gas versus 10% blend. No difference in mileage between 87 or 93 octane. Better performance/power observed using 93 octane & tune, but not enough to warrant the cost/price of the higher octane.

The price of pure gas around here is about 30 cents a gallon more than the 10% ethanol. Even if it DID give [my truck] better 1-2 mpg better mileage, it still would not be worth the price/use.

It's your truck. Do what you want.

 

Cool thanks for the test info. This should help dispell old school info

 

On paper, that doesn't make sense that there was no difference. That's interesting.

 

When I had to start using 10% ethanol, with my 5.4, I lost 1.3 to 1.6 mpg from then on. I keep an extensive spread sheet and I don't think it lies to me. This was on about 90% highway driving.

 

I've got gas stations here that offer 87 with 10%, and then straight 89 and 91/93 octane. I run 89 straight and been doing it for 5 years now, ever since my Ford dealer told me to run it when I hear pinging at 87. I just run it straight 89 all the time, and it works fine. Sure, it costs a little more, but the truck seems to like it, a lot.

Unless you are S/C or T/C, there's no reason to run high grade all the time. Regular and Mid-grade works good at least in the 4.2l v6, and I suspect that it will work great in the 4.6l or the 5.4l.

Just run some Regain thru it once or twice a year, and that'll help keep the combustion chambers and injectors clean.

 

My results are different. I get a solid 1-1.2mpg increase my using non-ethanol fuel vs 10% ethanol, same octane. I kept an excel spreadsheet for a few years for every fill-up. I have a stock truck (5.4L Screw) aside from the Gotts Mod and a SIDO Magnaflow muffler, no programmer. As long as the price is within $.20/gal of the E10, I will break even on cost per mile. If it goes above that, it costs more to use zero-ethanol, but I still get better mpg's out of it every time, hands-down.

As far as using 90 octane vs 87 octane on a stock truck (w/no forced induction), there is no benefit at all to using 90 octane. It resists ignition more than 87 octane, but it won't give you any more "power" because the engine isn't designed (compression) to take advantage of the increased octane, nor is it modified (programmer, ignition timing) to use it.

There is a point where using too high an octane is harmful and detrimental to power, because the engine has too much difficulty igniting the high octane fuel due to it being so resistance to ignition, but that's more of an issue with 100+ octane avgas or race fuel. Either way, no use in running it in your truck for no benefit.

 

I'm not sure what your concern is... The lack of an oxygenating agent? The computer will compensate, and chances are you will get better mileage.

Are you concerned about the octane rating? 90 is 3 points higher than the 87 minimum, so you are good there... Like mentioned above, the octane ratings that are hard for lower compression engines to fire off are much higher than 90 octane. I believe even the owners manual on my 04 says that 93 is good as well... I just wouldn't go over say about 95 or so... Not without forced air induction, or bumping compression up...

You lose about 10% MPG with the standard ethanol blend gasolines, so yeah, you SHOULD gain 10% MPG back...

 

I ran 87 fuel and currently have a 89 octane custom file. Truck doesn't run any differently than it did with 87, but there is a lot more soot on the tips with the 89. I like that because the spark plugs must be getting cleaned out some with the help of some techron.

Also ran 93 in my previous 2004 tuned, ran like an angry animal, but mpg didn't improve any.