87 vs 89 custom tunes
 

hi all,

Ive got custom tunes made for 89 octane. Would it make a huge difference if I ran 87 octane on these tunes?

It is highly recommended to not run lower octane than what the tune is written for. It is possible, and that change probably wouldn't do much, but I would be careful and slowly test it out and take notice if anything changes for the worse.

I'm gonna say dont do it because if the fuel causes too much knock the truck will pull a large amount of timing.

Thats what i thought. That could be why my tow tune didnt feel as strong as it should. Would it make that much of a difference if I had Bill rewrite my tunes for 87? Or should I just quit being such a cheap *** and fill with 89? Would the same issue apply if I ran 92?

thanks.

Having Bill rewriting your tune to 87 will let you run 87. I dont know if it would for sure run stronger but you wont risk major engine damage.

If you dont want to buy another tune then you'll just have to run the higher priced gas. You can easily run the higher (93) octane because it has properties that make it more stable than what the tune requires. You wont see all of the benefits but it wont have any bad effects. Running 89 allows it to run as it is was meant to be run but 87 does not have the properties to run correctly.

I THINK, since we're talking only two octane points here, that if you use an 89 octane tune with 87 octane gas, you'd probably be all right if you set the timing down -1.0 in the Custom Options Menu.

Bill MAY have made some slight fuel adjustments and other slight tweaks, but I doubt anything is as critical as the timing.

Don't hear me saying it's OK to use a 91 or 93 octane tune with 87 octane gas though, because that's too big of a jump.

You can ALWAYS burn higher octane gas than the tune calls for though, if you want to throw away the money.

- Jack

Ive emailed Bill but havent heard anything back yet. The gas station i frequent sells 87 or 91... go figure.

Go with Jack's recommendation.

Use 87 but back off the timing a degree or so in your custom options menu.