I'm running 93 with the 91 tune on mine. I've only had it installed for a couple days, so I'm still getting a feel for how the truck behaves. I noticed the change in the shifting right away and the truck does feel more responsive. I've also noticed that the truck will break the tires loose about half way through first gear and it didn't do that before. After I run this tank out I'll probably switch to the milage tune and see how that goes.

I was messing around in some of the advanced settings today and noticed something odd with the tire size. The truck is set to a 28" tire height. I have the stock 245's on it which is the original the truck came with. If you calculate it, the height for this size is 29.5" Prior to having the tuner, I never noticed any issues with the speedo being off, it's even always been right on with readings given from the electronic signs that I sometimes come across out on highways. Should I change is to 29.5?

 

I asked SC tech that same question. They said to measure tire diameter from pavement to top of tire while mounted on the truck. In my case the tire height spec is 30.6 but the measurement was 29.5. So I set the tuner to 29.5.

Speedo agrees with my GPS.

 

Yeah I checked mine, and it measures 28". I tried two different tire calculators and they both came up with 29.5". Why is this? I guess I'll leave it on 28 then.

 

Just curious, but when running a 3865 programmer, do you have to run 91 or 93 for the performance tune?

 

The performance and towing tunes need 91 or higher.

 

x2

 

And what happens if you run it with 87 or 89...detonation?

 

My guess is that that youd be fine, but the knock sensors will just retard you back down to crappy performance and mileage.
There are several electronic perameters adjusted for a specific tune. Youd be safe for a tank or two, but not as efficient, so you might as well run the right tune for the fuel instead of "bumping" off the sensors all the time. The only way i can see it being a problem is if you had a sensor failure, but that would probably through a code/CEL.
PS. I dont have a tuner, but this is from my own research as I hope to soon

 

I guess it's safe to say I also hope to have one soon. Looks like I'll be hitting Sunoco for their $.05 off a gallon for Ultra on Wednesdays and Sundays after I get one. Ha

 

Haha, that's probably what I'll end up doing. I prefer their gas anyway.


Keep in mind that not all of the 4.7L engines have knock sensors. As far as I know, the only ones that do are the HO and the E-85 capable engines. Somebody please correct me if I am wrong.