91 Or 87 Tune For Mileage?

[rt66er]

I have a Hypertech Max Energy tuner with the 87 octane tune installed. My question is: would I be better off (mileage-wise) running the 91 octane tune? I'm currently averaging 18.8 mpg on 87. Just to break even my average mileage would have to improve to 20.0 mpg to make up the $.22 gallon higher price of 91 octane over 87. Would it be unrealistic to expect that kind of improvement? I suppose I could just run a couple of tanks of premium to find out, but I though perhaps some folks here could offer their own experience.

[95Sierra2500]

If you're not knocking with 87, you probably won't realize much of an improvement going to premium. The only way to really tell though is to try it.

[fbachman]

As I am not familiar with that tuner (or their tunes). In particular, the issue comes down to whether the tune (going from 87 to 91) changes the thermal efficiency of the engine (by virtue of timing, shift points, etc..)

 

I CAN offer you my experience with the DiabloSport Tuner:

 

I saw a SLIGHT mileage increase going from 87 to a 93 tune where I jacked the timing to the absolute limit for 93 gas. I do NOT believe that you will improve from 18.8 to 20 going from 87 to 91. You may see a slight improvement--- if it is detectable at all. But, in the winter, everything will take a 10-15% dive anyway (mpg).

 

Going from 87 to 93 brought significant timing changes to improve engine and combustion process efficiency to where I detected approx 1 mpg increase in the long run.

 

It also comes down to how much you value drivability and performance improvements. Although my mpg didn't improve enough to justify the economics of running 93 over 87, the truck's performance increase was exponential over stock.

 

I guess it just comes down to whether you are focused stricly on mileage, or you value performance improvement, and which is MOST valuable to you.

 

All of this, of course, assumes that driving habits remain consistent between the tunes. A hot 93 tune does tend to make your right shoe a little heavier, as it is therapeutic to mat the pedal and have the truck fly away.

 

Hope this helps.

[rt66er]

Thanks for the reply. Kinda what I figured. I am currently happy with the performance of the truck so if paying for premium offers no significant improvement in gas mileage, I guess I'll not worry about it.

[csheatz]

Since this is a good topic i might as well add my own questions!

 

 

Would I gain anything running 93 on a stock set up? I thouhgt i read on here that while towing running 93 will get better mpg's. anyone have opinions on this?

[C & A s Dad]

Chris, there are opinions on both sides of the fence on this topic. I run 93 all the time and did so even before I tuned for it with the Hypertech. Your engine can certainly take advantage of the higher octane but the increase in MPG and power will be slight. The 93 octane will allow your engine to run more timing before knock or ping is detected by your knock sensors. This provides more power and better mpg but nother dramatic. With 87 octane ping comes in sooner and causes your PCM to pull timing back to stop the detonation. With 93, the ping will either not come at all or will come in at a much higher degree of timing.

 

Even before I tuned, I was convinced I could feel a difference when towing with the 93 octane and my Interceptor scan gauge showed almost no timing being pulled when towing with the higher octane.

[csheatz]

Well i am going to give it a try, i am prolly going to need gas friday or so ( 1/2 tank last about 2 weeks. and i dont let it get much lower then that). I am going on vacation 2nd week of sept so i will watch for a difference towing. i would be happy if i got more then 11.5mpg towing but i wont complain because i know people who get under to 10mpg.

 

 

I have a scan tool that allows me to monitor all those things but when i plug in and start up the lock icon lights up on my dash, so i turn off and unplug it..... then everything is fine. Is this normal? i like keeping a eye on things once and a while but i dont want to cause a issue.

[C & A s Dad]

Chris, I am not a Technician but have been told that it takes about 2 to 3 full tanks of premium fuel before your engine will adjust to take full advantage of the increased octane. I am telling you this just so you will know it may take a little while before you reap the full benefit.

 

My Interceptor Scan Gauge is a permanent mod for me and it does not lock anything as you metioned. I typically keep it set to read trans temp and MPG but sometimes when towing I will set it to read trans temp and knock retard. The most timing I have ever seen pulled it 3 to 4 degrees and this was on a very hot day pulling my 6500 lb camper. It pulls the timing in a millisecond and adds it back in over the next 3 to 4 seconds.

 

I do not think you will see any better mpg than 11.5 while pulling your camper.

 

Just like my Dad has always said: "If you want to dance, you gotta pay the fiddler."