Spark advance?
 

I am playing around with my "Transmission Only" stock tune to see what I can do for max fuel economy. What is a "normal" amount of spark advance at 87 octane? It's at 1.25 right now and seems fine. Do I keep bumping it until I get valve rattle, then back down one notch? That's pretty much the drill I remember from adjusting a distributor long ago.

Thanks.

Unlike the distributors, these modern vehicles are able to retard timing if it becomes over advanced.

Have you tried running the other tunes? For me, the tow tunes get me by far the best fuel economy.

I have. I ran the stock towing tune until I got my 87 Custom Performance. I have run the 87 Performance for about 8 weeks. I'm just playing around with it. Initially it looked like I was getting better MPG. but it was because my wheel size got whacked when I switched tunes. I've just about got that dialed in so I can make a good comparison. I must remember to WRITE IT DOWN this time. It seems that the tranny only tune is doing a hair better on gas, but I can't tell until I get the tire size right. I guess then I could do a tank on each (all three) and compare. Is there a "normal range" on the spark advance?

What kind of mileage were you getting on the tow tune?

What do you mean by range?

Also, which programmer do you have?

Seems like the tow was about 14-14.5 (about 70%city/30%highway.) Seems like Custom 87 Performance was a shade better. Truck is on '04 SCrew 5.4.
Tuner is the Gryphon (original, not CTS) I'll be doing a little more highway driving this weekend. Curious to check it there. I once (only once) got 18 an an all highway trip. It was before the Gryphon, but I had fresh oil/filter. I'd love to see that again.

Oh....range. I mean "what degree of spark advance is normal/acceptable with our trucks?" Mine's at 1 or 1.25 right now. Just curious if I should advance it more, leave it alone, or back it down some.

one more time. I'm talking about the TIMING setting in the "Custom program" options. Sorry. I do realize that the advance changes automatically under load.

The typical setting is 0. This doesn't mean that the advance is zero but the degrees of advancement from the baseline is zero.

If you advance it too much, the computer will automatically start pulling timing. Often it pulls in large amounts and makes people think they need to then advance more. You probably aren't at the point yet but if you keep a spread sheet and have a very regular route, you'll be able to see when it yanks a bunch of timing because performance and mileage will drop. I would not keep raising the timing advancement without running higher grade fuel.

Perfect. That's what I needed to know. So, do you think I'm ok at 1.25?

Without sitting in your truck I can't say for sure. I will say that if you were to carry that 1.25 to the level 2 or 3 tunes, you'd probably be asking for trouble. Basically you are only adding timing to the stock engine tuning.

I should add things like cam timing are modified in the other tunes, which is why you can't drop the ignition timing to run low octane on a high octane tune.

Your mixed driving looks pretty good. I have a spread sheet with a weighted average for mileage. I'm currently sitting at 45% city driving with 14.8 mpg on nearly 6000 miles.

Also, do not trust the electronic MPG displays, they all lie. Only use hand written or spreadsheets.