I have the tunes from Tillmanspeed and I am running the 87 octane tune right now, and I want to change to the 93, but I don't know what I need to do. Should I run my tank of 87 to almost empty and put 93 in and drive till it's gone and then put a second tank in and then change the tune? Basically...when should I change the tune?

Thanks

 

just run it as low as you can. say, 30 miles left or less. Then fill all the way up with 93. You should be good

 

I usually run it down untill the cluster says 3 miles till empt. Then fill it up with a gallon 91octane but keep the 87 tune. Then once I get to 3 again I refill the whole tank with 91 and then change my tune to 91R. You could probably just run it down till near empty, fill up with 91 then change to the 91 tune. I'm just a little paranoid.

 

So I fill up with 93 and then load the tune? I just dont want to mess anything up.

 

As long as you get it down to almost nothing (my 30 may have been a bit much, probably more like 10 or less) then you'll be fine. That tiny bit of 87 in there won't hurt it. I had like 1/4 tank left of 87 and got a 91 tune, so I went and filled the rest up with 91 and dumped a gallon of unleaded race fuel in there. But I wouldn't suggest that, if you're worried.

 

Not sure of the most optimal way to do it. I was timid about just filling up with 93 once then loading the 93 tune. So I ran my last tank of 87 down to 30 miles to go, filled up with 93, ran that down to 10 miles to go, filled up with 93 again, then loaded 93 tune. No knocking at all with that. You may be ok with only filling once since I think the S197s have a knock sensor but I wanted to be sure so I filled up twice with 93 before switching.

 

I think I ended up doing it twice while waiting for my tunes but cant remember . 1 should be ok 2 I think is going the safe route and should be considered, especially if you get pingning when you load the 93 tune.

 

When I was on the phone ordering my combo from Doug that was the one question I had for him. Just drive the tank down below 1/4 of 87, refill w/ 93, run that down alittle past 3/4 tank and refill w/ 93 again. Good to go....

 

You might want to be more paranoid about running the car down to "3 miles till empt." The electric pump in there relies on the fuel to keep it cool. Running it to near empty can overheat the pump...not a big issue from time to time...but I wouldn't make a practice of it.

 

Do what Doug says...end of story

 

Um, the computer shows 0 miles to empty with nearly 2 gallons left in the tank. Let it go to 0, it will take about 14.4 gallons of fuel, a little more if you top it off manually. 30 miles to empty=roughly 3.75 gallons left. Just let it run to '0', fill it up a quarter tank 93, run it to '0', then fill it up. It will be just about 'pure' 93 by then.

 

i don't get it. Why is it so much safer to run a 87 tune on 93, than run a 93 tune with a small amount of 87? Either way the computer will pull timing or do what it needs to do to keep from engine failure, but a small amount of 87 on a 93 tune sounds safer than a large amount of 93 on an 87 tune.

 

I'm pretty sure it sorta doesn't work that way. Read http://en.wikipedia.org/wiki/Octane_rating
Basically gas with a higher octane rating is more resistant to igniting than lower octane. This is why you can advance the timing on a 93 octane tune (getting a more powerful ignition) and not put the engine in danger of getting ignition early. If you put 87 octane on a 93 octane tune you run the risk of having the ignition happen at the wrong time creating engine knock. Read http://en.wikipedia.org/wiki/Engine_knock
But you can put 93 octane in with an 87 tune and still have the ignition happen right when you want it for an 87 tune because the 93 is MORE resistant to ignition, not less.

 

Explained in Laymans terms

 

Gotcha. That makes sense. So why is my stock tune for 87 in my '07 pulling timing over 5000RPMs when running 89? Oh well, new tune/intake on the way.

 

Seems to be a common trait among us peoples.

 

How do you know it is pulling timing?

 

I put it on the dyno and at 5000 RPMs the AFR dropped from about 12.3 to 10.6. The second run was even worse. The dyno guy said the computer was probably pulling timing to compensate for something or other. I don't remember his exact words. The dyno sheets weren't pretty. That was on shell gas. I thought shell was supposed to be better. When I get my intake/tune in I'll fill it up with the Ford recommended BP and see put her back on the dyno to see what happens.

 

I am no expert in this matter, but pulling timing shouldn't affect the AFR should it?

 

As stated above, it's just about getting the mixture of the old 87 octane down as low as possible. Getting it down to like 1/8 of a tank and filling the rest up with 93 will get it started real good, and it will mix with the 93 that you're putting in to produce something around 92 octane so-to-speak. By the time you run that down to anything less than half a tank and refill with 93 again, you're good to go.

Even with just running the tank as dry as you can and filling up with 93 should be close enough to run the tune without knocking, etc. Adaptive learning is a lovely thing (sometimes)!

CR
Tillman Speed