Up until a couple months ago, I was running 93 octane with the SC 91 tune. I appeared to be getting about 12.5 mpg. Now, since 93 is up over the $3 mark, I've put it down to the 87 tune..running 87 octane, and I seem to be getting about 11.5-11.9mpg.

Does this sound right?

What gas/tune combo are you running?

 

Sounds right to me, I have always gotten the best mpg's out of the 91 tune with 93 gas.

 

wow i'm in the high 14's with no tune and straight 89. Why do I need a tune??

 

I wouldn't run 87oct just because of the prices. The little you save you loose in mpg's and besides, if you have an owners manual.....It states that 89 oct is highly reccomended. Although it should say mandatory because the damage 87 oct can cause can be severly damaging.
Most of the engine troubles that I have seen or heard have been from piston damage due to pre-detonation from using low grade gasoline. These engines are very prone to detonation and damage. The pistons get damaged and the skirting breaks off in chunks because the ringlands are extremely close to the top of the piston like they are in racing engines.
If you think that because you can't hear it, that it's not happening you are wrong. It's something most cannot hear unless the detonation is super bad. it doesn't take super bad pre-det to kill an engine either, just takes constant abuse over a short period of time is all.
I am running 91tune with 93oct. and I get better mpg's than the 93 tune. I have not even tried the 89 tune so i cannot comment.
I will say that since I raised my shift point up, my mpg's have def improved by 1-1.5mpg's in the city. Highway stayed the same.

 

I also run 91 tune and 93 octane, but I dont have a hemi!

 

good reply post ddog. ^^^ nice job!How did you sneak in smoke?? lol

 

Is this the cause of the famous Hemi-tick?

 

Im running the 87 diablo tune with 89 gas, and I tend to only go to the gas stations that dont use ethanol, so I get about 15-15.5ish with my mixed driving.

 

no! the hydraulic lifters by design cause the hemi tick. A perfectly torqued head will still deliver the "hemi tick". No reason too panic it's one of those thinge that we hemi owners have to live with proudly I might add.

 

This has been discussed many, many times on here.

#1) That's about right whether you are running a DSP or SC. Of the canned tunes, it still costs a little less per mile to go with the performance tune and paying extra for 93 octane gas.

#2) 'Dog is 100% correct. As I've stated before, I have been keeping a kind of unofficial track and it seems that EVERYONE who has had a major cylinder failure in a Hemi, has been running 87 octane fuel. That said, I've had people tell me they have over 175k miles on theirs and NEVER ran any octane other than 87. But if it were MY truck, I'd not take the gamble. I've also had people swear to me that they are running a performance tune and using 89 octane gas AGAINST tuner specs. I've seen the amount of timing advance in these tunes and NOT running a premium fuel is just stupid IMO.

#3) The octane recommendation has nothing to do with the famous (infamous) Hemi tick.

#4) There are MANY other benefits to running a tune besides gas mileage...