Rule of thumb ignition advance

[mashaffer]

I know each car is unique in what timing it likes or allows but I was wondering if there was a rule of thumb on how much additional advance you can dial in with increases in octane. For example if your car allows for a certain amount of advance on 87 octane can one say that you can generally add X amount more for 91 octane or Y amount more for 93 octane (just for planning purposes obviously).

Also does additional advance typically improve mileage somewhat also so that better efficiency partially offsets the higher fuel cost of going to higher grades to allow more advance.

mike

[gadget73]

Really kind of depends on the engine. I've known people with stock engines that ran 4-6 degrees extra advance on regular. Mine have always pinged at anything beyond the stock setting. Since they rattle and carry on, I've never left it advanced so I can offer no experience about what benefits it may or may not provide.

[DerekTheGreat]

Ashley's 1989 TC is running the base 10* now and getting fantastic MPG. We had it at 13 but I noticed when I was driving it would ping on the highway and under load, didn't do that when it was initially set there. Then I just started backing off on the timing until it didn't ping, which worked out to be the base 10. My 1988 TC is running at 12 degrees and is happy there. It also pinged at 13 but never heard it due to radio most times. I'm also seeing better MPG. It really does depend on the engine and how well it was maintained, you'll just have to play it by ear as you advance it or leave it where the factory intended. I don't like to run anything other than goat piss in my daily drivers so running higher octane for slightly more power (if any) isn't worth it for me.

[merc91]

To much is as bad or worse for power as to little, believe it or not my combo likes bone stock timing on 87 and 2* less than stock for best wot power.
If you have a track around with $20 test and tune night, make runs spanning 7/9/11/13* and assuming no spin, go by et and a little input from mph, if spin is questionable go by mph and you should have a nice curve with the peak in that range. I find 91-93 higher octane burns faster once lit and likes 2* less timing than 87.

So many people run as much timing as they can without knock but that is 90% of the time hurting power