Dakotaho was on target. There is no mileage difference between the 87, 89, or 92 octanes. Your ECM will retard the timing to stop any ping before it would actually happen. You should never hear a knock or ping on an ECM/EFI engine. If you are pulling or hauling a heavy load, you would benefit by using the higher octane. Your mileage would be better because the timing would be at optimal settings rather than being retarded to address the pending detonation. In most situation, 87 octane would be fine, but under WOT, you might be missing a few horses, especially down low in a high torque situation like getting a fat truck moving. This would be compounded by some of the high axle ratios and 20 inch tires that many of these trucks have.

 

Certainly true, run 87 octane with the stock tune, your ecm pulls timing, you loose horses. I saw this when doing dyno pulls on the F150, gas station in VA ripped me off, I thought I was getting 93 octane at a Citgo. First dyno pull, tuner said I was running crap gas on his 93 octane tune. I showed them the gas receipt. He showed me the knock sensor was pulling timing and I lost 14 horses. ( and was basically ripped off by the gas station ). To prove this we dumped two bottles of octane boost in and jumped around in the truck bed and tail gate. Next two pulls, I was +14 hp over my first pull with no timing being retarded and no tune parameter adjustments were made. Amazing what you learn from a good tuner. This new hemi was obviously rated at 390 hp on 89 octane and that is why it is the recommended fuel in the owners manual. Once Diablo gets any remaining tweaks done on their tune, the 87 tune would be a good investment if you want more power, if you do not mind waiting two years to break even saving .10 per gallon for 89 compared to 87 octane fuel to cover the investment cost...

 

I make more than enough to pay for the 89 and not "break the bank", but why would I do it if I don't have to? Seeing as 89 is close to, if not more than, 10 cents more than 87 here, I am probably looking at least $500-$600 more per year in gas costs. Thats a big difference more than $3 a week. If 87 will work just as well then putting that money elsewhere makes a little more sense to me, than needlessly burning it away.

Alot of people say 87 gets better mileage and 87 has never hurt their engine.....then theres an equal amount of people who swear that 87 will damage your engine if used over long periods. Seeing that the owners manual says 87 is acceptable to use I just wanted to hear opinions.

 

Medic,
87 will not get better mileage, just as the higher octanes will not get better mileage. Octane does not effect mileage, only prevents detonation. The only time the higher octane will use less gas is if you are hauling a heavy load that would cause the ECM to retard the timing with 87 resulting in less power AND you compensate with more throttle to maintain speed. The higher octane would only save a small amount of fuel during the above situation. If you were pulling a heavy trailer in the mountains for a full tank load, you would benefit most from a higher ratio (lower gear) axle. Most people don't understand in a normally aspirated engine, the higher you go in elevation, the less HP you can make and detonation is less likely. That would make the higher octane less important anyway. I run 87 in my hemi about 60% of the time. If you are on a highway with no load other than the truck, 89 and higher is wasted money IMO. You will not damage anything due to detonation, because it will never happen.