why would you run the 87 tune with 89 octane? if you're going to run 89 anyway, use the tow/haul tune or something.

 

i dont tow or haul...

 

Tow/Haul tune on a SC 3815 requires a min. of 91 octane. DO NOT attempt to run that tune on 89 octane fuel. Pre-detonation will result, especially if putting a load on the truck.

There is no harm in running the 87 Tune with 89 octane fuel, however, because the truck is "de-tuned" you will gain no benefit in performance in spending the extra money. In this sense, 'Feej is correct, you can save the dime or so a gallon and run 87 octane fuel...

 

thanks hammer...wasnt gonna do it anyway. im happy with the 87 tune

 

you don't use 87 octane either...


I thought tow/haul required 89 octane? If it does require 91, then I was very wrong.

What I'm getting at is you are in effect de-tuning your engine by using 87 tune as opposed to a tune designed for 89. If you are going to use 89 anyway, get what you can out of the motor with that fuel.

 

I use to love the 87/89 combo on my truck when I first got the tuner. I tried the 87/87 and it was alright but didn't feel quite right, but for one reason or another the 87/89 just felt much much better (probably no difference between them but the truck just felt better). Ran the 87/89 combo for about 6months or so before I tried the 91 tune and haven't switched back since. It feels much smoother than the 87 tune, and for the extra $0.10 a gallon I was getting better mileage off the 91. With the 87/87 & 87/89 I was in the high 13's to low 14's for mpgs and with the 91 it brought it up to the high 14's to low 15's for mpg consistantly.

 

The 87 and the mileage XS I believe are two completely different tunes but since mine is so old I may be wrong on that.

 

You would be correct, however, both are written to allow the use of 87 octane fuel.

and 'Feej, I know for a fact, when you go to program your truck with the Tow Tune, you get a big warning box to use 91 octane fuel, same as you do when installing the Perf. Tune. But here is a direct quote from Ron @ Superchips:
"The Tow Tune is a great for towing and hauling but it still requires 91 octane as does the Performance Tune."

 

gotcha, my mistake then.

and in that case, why don't they have a tune that just takes full advantage of 89? hmm, might be something to mention

 

If you read post after post on the Flashpaq forum, you'd see 80% wanting to either ditch TM or getting a 93 Octane Tune. Used to be just as many wanting to ditch 2nd Prime, but they gave us that. I've not seen the first person wanting an 89 octane tune yet...