Kind of a simple question I've been searching for weeks, no responses I found helpful to date.

Simply, I have a edited custom 87 tune Bill fixed for me. I switched to the 93 canned. Can I bump the timing the correct increments to 93 and safely run it?

 

John - forgive me, are you saying you want to run an 87 octane tune with 93 octane gas and increase the timing to compensate for the increased knock resistance? If that's your question, the answer is "yes" - But I think I'd advance the timing in "steps". Possibly try 2.5 degrees at first, then 2.75 and finally the full 3.0 degrees if things seem ok.

Timing adjustments are not really "precise" things (due to manufacturing differences in each engine) and gas octane is not necessarily too exact either. So, it's best to "sneak up on it".

- Jack

 

You got it my friend The 87 is a custom tune, which is why I was unsure if it could be done. I'll have to give it a shot. It's great having you around to help with stuff like this Jack

 

I wouldn't.....different A/F tables are used besides the timing curves....

Sorry Jack but I disagree, custom tunes have a lot less play than canned tunes do.

JMHO

 

No offense taken, my friend. I'm simply going on what Bill Cohron has said (by way of Corey) - "It's not a problem to use high octane gas in a low octane tune and increase timing, but it CAN be a problem to use low octane gas in a high octane tune while retarding the timing."

I certainly recognize though, that you're not going to get the "best" out of your powertrain with that setup. But, PHP has said there shouldn't be any danger of damage when using the high priced liquid in a low octane tune.

I wonder about A/F ratios too. Would high octane gas have a different stoich than low octane? I know ethanol changes the stoich, but knock inhibitors?

And, I recognize that a tune for power does involve a slightly lower stoich setting than the "optimum".

So anyway, John - now you've got two "opinions"! Each one's probably worth exactly what you paid for them.

- Jack

 

I would not use a timing adjustment for that big a difference. It's fine to adjust for 93 on a 91 tune, but to adjust for 93 on an 87 tune is just more than I would want to run. I would not have a problem of bumping for 89 on an 87 tune.

 

Please excuse my ignorance, but what would be the purpose/benefit of running 93octane gas w/an 87 tune or vice versa? Why wouldn't you just run 87 gas w/the 87 tune and 93 gas w/the 93 tune?

 

Let's say you run a 93 perf tune 99% of the time......
Yer buddy calls you up to come pull a trailer TODAY.....you want to switch to yer 87 tow tune cause you don't have a 93 tow tune and the night before you just topped off yer tank with 93.

You can't go 87 to 93 but with adjusting the timing you can go the other way as J+J pointed out but I do remember that situation was for towing and not performance tunes.

I do agree with Bluejay that it is a big step......

As a general rule of thumb you should always get a tow tune in the same octane as what your performance tune is.

 

Oh, okay that makes sense. Thanks for filling me in!

 

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