I've run all three grades & haven't noticed much of any difference. I assume there maybe a mpg difference, but I haven't been looking at that for one main reason: I end up driving like a wuss if I watch the mpg readout. I now keep it on the temperature readout.

 

Guys, gasoline blends vary from state to state and season to season....winter gas is not the same as summer gas and all the mixtures that come in-between. Focus on your car/truck, not the gas...

 

How do you know when your car needs what gas, like at what compression ratio do the needs switch. What I want to find out is, my friend has a 99 Trans Am with the LT1 and he pumps premium, and all of us are say why you do that because all the other people with camaros and birds, pump regular that I know, he says that he needs it, he usually buys more expensive stuff to show off, but ya he said he needs premium according to his manual, we don't believe it, as my mom pumps regular into her camaro and always has, but I figured I would ask you guys for some input, since you probably know better than me.

 

I take that back he has a LS1 engine not a LT1

 

OK..here's how I understand it. The Hemi combustion chamber design causes cooler exhaust exit temperatures. This means the exhaust will contain more CO. This CO emissions trait was one of the reasons Chrysler couldn't economically get the 426 Hemi in the early 1970's to comply with the ever-stricter emissions laws. The 89 octane fuel burns hotter on ignition and burns more completely than 87 octane. This keeps the CO emissions in check. I believe I read one of the engineers greatest tasks in designing the new Hemi was dealing with the CO emissions.

I don't believe 87 octane will hurt necessarily, but I'd rather burn the 89. I've had 87 in my '04 Hemi QC 4X4 and did notice a bit of detonation, but no other ill effects.

 

Well gentlemen, I suspect this question will get as many answers as there are people reading it, but I have a different one. The truck manual does not say that you have to use 89 octane. It says that 89 is recommended for best performance, but that 87 octane is perfectly acceptable.

I have read many posts' on this, and other boards, about some people claiming pre-ignition "knock" if they don't use 89 octane. I have also read just as many that say they have no trouble with 87 octane and could not tell any difference in performance. My personal experience is that 87 octane is just fine for my truck. I tow a TT with it quite often and have no problem at all with 87. Now, the question is, would it do any better on 89? Not according to my experience, all I noticed was that my wallet was a little thiner when sitting in the truck. That covers performance, as far as I am concerned, at least, now how about longevity? That's a question for all to ponder, I have not had the truck long enough to make an evaluation on that, but it seems to me that, if it was detrimental to run the 87 octane, Dodge would not be doing us any favors by not saying so. As long as the motor is in proper tune and is not "knocking" I think it is O.K., I am sure there will be some to disagree.

If my Hemi ran any better I couldn't stand it. I noticed yesterday, after changing my synthetic oil, that the loudest sound when my engine is idling is the woosh, woosh, of the fan blades as they turn, you can hardly hear another sound. It's not much louder at 3000 RPM's either.

 

I have also addressed this issue on this forum when I purchased my Hemi 5.7 almost 4,000 miles ago. I have experienced no problems and no noticeable difference of any kind running on 87 Octane... I too tow alot, that is why I bought this truck. I have a 3.92 rear end gear ratio and I have been very pleased with the economy at 18+mpg's on the the highway when not towing....

I do seem to notice a difference in economy when I run 87 Octane with 10% ethenol, it seems to not do as well...