i have a question, do yall hemi owners run 87 or 89 octain in your trucks???
it says in the my manual, that the hemi requires 89 oct. , no one told me that at the dealership???
anyways, my truck is a 2004, so idk please tell me

 

Here's a couple of threads (searched on "octane" in 3rd Gen Forum), there are more.

https://dodgeforum.com/fb.asp?m=849293(July '07)

https://dodgeforum.com/fb.asp?m=961370(Sept '07)

Personally, I used 87 for the first two months of having my Hemi. I didn't read the manual, and didn't hear the dealership mention anything about it. Then folks on the 3rd Gen forum mentioned that the factory recommends 89, so I finally RTFM and switched. I'm on tank #2 of 89..... subjectively I sense better throttle response and seem to be getting better gas mileage. I'll have more fuel consumption data to analyze in six weeks or so to perhaps draw a conclusion on how much moreefficient my Hemi is on 89 vs 87 under my driving conditions. A couple of folks onanother web forum say that they experienced better mpg on 89.

 

I would probably go with the 89 also. I don't think there is a HUGE difference in the immediate performance but you probably get a little better MPG using the factory recommended octane. Down the road your engine will be better off using the 89 over the 87 as well. I have a 06 HEMI and when I bought it they filled it with 87 but the service guy told me to use 89 for sure. I couldn't tell much difference but if it preserves the motor down the road than I'll go with it. Of course, with a 24 gallon gas tank the $$$ difference between 87 and 89 over the course of a year could be substancial.

 

The computer will compensate for the lower octane by retarding the timing slightly. This will give you slightly less HP but shouldn't affect your mileage, exceptwhen haulinga heavy load where the extra HP would come into play. I've been running 97 almost exclusively and get exceptional mileage if I keep my foot out of it. I only use 89 when I'm towing or going intohigher elevations. I also wouldn't worry about longevity.As long as the computer can compensate (which shouldn't be a problem except in high elevations or under heavy load), then the motor won't be harmed in any way. This is true of any modern, computer-controlled motor, even HiPo motors, such as in my Crossfire, which has 10/1 compression.