Guys, if I am running a 93 octane tune and the only gas around town is 91 do I back the timing off to -1?

Lets say I am in the mountains and only 87 is around, would that be -3 from a 93 tune?

 

From page 17 of the Gryphon manual:

On the surface, you are correct. However, if you detect pinging, the ECM will retard the timing and your performance (and MPG) will really suffer.

Most of the time you are better off increasing 1/2 degree at a time until you detect pinging. Then decrease 1/2 degree.

So in your 91/93 scenario, if you're not detecting any pinging, you should be fine. If you are, try decreasing 1/2 degree. If you're still pinging, decrease another 1/2. You may even have to go to 1-1/2 degree.

Personally, I wouldn't run 93 performance on 87.

 

How audible of a ping are we talking about? I thought the motor has knock sensors on it that will pick it up before our ear can even hear it if I am correct? I know my 98 cobra had this situation when it was boosted.

 

The knock sensors can help you within a small range. I believe you are safe at high altitudes (5000+) on mountain gas that's 2 points lower. I'm running stock and have never heard a ping on 85 up there, and it gets excellent gas mileage. I would not run a 93 tune in California, period - get a good 91 tune and have an 87 tune available.

If you hear ANY ping, back it off.

 

I've never had a pre-detonation issue on my trucks (well, I did on my 91 Ranger), so I'm not sure how long it takes the ECM to retard the timing after pre-detonation is detected.

It's my understanding that the engine can still ping for a brief period until the knock sensors retard the timing. You could use the spark advance/retard PID to monitor the timing.

 

Ping = put some marbles in a tin can and shake.

 

I am assuming you are running a 93 custom tune. Yes, back the timing off 1.0 to run 91 octane. If it is the canned level 3, it was written for 91 octane.

 

There aren't too many states left where you can get 93 octane anyway. 91 and 92 is becoming more and more common, and in the mountains you are going to get 89 to 91 at best for a full premium. You will also find stations that don't even have a full "premium" any more, just regular and midgrade (89).

 

Thanks guys exactly what I was looking for!