I currently drive a 02 F-150 XLT with the 4.6 L V8 engine. Someone told me that the V8 runs better on 89 octane even though the owners manual says run it on 87. Do engines really run better on 89 octane?

 

The higher the octane rating the better gas mileage you get.

 

Octane is a factor of gasoline that tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes damaging knocking in the engine.

Lower-octane gas ( 87-octane gasoline) can handle the least amount of compression before igniting.

The only benefit to higher octane gasoline is that you can use it in an engine with a higher compression ratio. More compression makes more power from the same amount of fuel.

If your engine has a compression ratio of 9.5:1 or less, it will run fine with 87 octane. --It will not make more power with 89 octane.
--It will not get better mileage with 89 octane.
-- It will cost you more $$, however . . . .

 

Boy, this is such a common question, with so many different answers. I'd agree that octane rating itself will not make a difference in power or mileage, except if the vehicle's computer has the ability to increase the ign advance to a point where it can 'take advantage' of the higher octane - i.e. increase to the point of knock. I have no idea if the 4.6 or 5.4L has such capability (i.e. range) but given the low compression I'd doubt it. Different gasolines do have different formulations (such as % of methanol) that could make a difference in power and mileage - changes to the formulations are mandated in many (all?) states depending on the season. I've heard that many even 'branded' stations may get their gas from different sources so I'm not sure how you'd actually know what formulation you're getting. It seems more like a crap-shoot than anything. My 2C is to save your $ and purchase the octane recommended (at least for a new vehicle where incr in compression from deposits is not an issue). If you find that the motor knocks, try a different brand (in my 428 the brand of gas did make a difference, but it really wanted 100+ octane - leaded gas solved that ).

 

The 4.6L and 5.4L do not have the ability to adjust for higher octane....the engine is setup to run on 87 octane no matter what may be in the tank.

Using a chip or tuner requires higher octane as they adjust the timing to take advantage of the higher octane gas...this is how they make more power.

 

Well, one week I had a little extra change, and put some racing fuel in (100 octane), yes they actually do sell it for $6 a gallon . But I tell you oh that baby did purr. (actually i had a little more than a little change, cost $89 for a full tank!!, never again) But I'd say it didnt do that much for the price.

 

Careful, Higher octane racing fuel sometimes contains lead ad lead will clog the injectors. Also, High octane fuel burns slower, and if you go much over 93, you can actually lose power. I tried it straight in my Mustang with 9.5 to 1 compression and it actually slowed down at the track. Went back to a 50/50 mix and it picked back up.
I have tried higher octane in my 2001 5.4L and only felt a lighter wallet. I do run 89 octane now that I have a Diablosport Predator to get more timing and power out of it.
RACING FUEL DOES SMELL GOOD THOUGH!!!!

 

the only time i would waste my money and put higher than 87 octane in my truck is if i was almost out of gas in the middle of nowhere and the only gas station i can find is one that looks condemed. tried higher octane gas before and the only thing it did was cause my truck to make a pinging sound and make the truck diesel. next tank i put 87 and it purred like a kitten.

 

i stick with 87. put 100 in my mustang at the track once so i could crank the timing, but thats it just kept it from pinging.