How much timing……. Now that is a question that hopefully no one has the perfect answer for.
Your gal will tell you how much she can deal with and this number is best found as you carefully move up the scale.
Meaning the 18-20 as being used for the 91 octane gals has become a good run of thumb however there is far more than the octane rating that dictates the maximum timing one can use.
1. Quality of the fuel; not simply the listed octane as all fuels are not the same
2. The stability of the discharge air temperatures; meaning do they fluctuate a lot based on differing driving styles and if yes then the worst case needs to be the bases for the tune.
3. The stability of the engine operating temperatures; as mentioned above this is important because if you tune with the gal in the 190 degree range however in real time she spends more time in the 210 range then the tune needs to be appropriate
4. How will the gal be exercised; for example a simply clear your head gear blast once in a while, long extend hard pulls, or maybe on the track because each of these will create a different scenario
5. Elevation at which she will be exercised
6. The engine load as the result of the static gearing as well as the gear and RPM at/in which you put the proverbial hammer down
Now with the use of quality 100 octane fuel is it possible to advance the timing into the 22-25 degree range; certainly however I would never do so arbitrarily but rather I would methodically and incrementally give a little at a time until she says “enough”
I would also make darn certain that in advancing the timing further that you (as close as possible) duplicate over and over the real time driving circumstance that she will be exposed to so as not to artificially mask what could end up being too much timing.
These gals have NO knock sensors other than your ears and or the ability to see things going wrong on the graph during a dyno pull meaning that unlike many cars of today that have knock sensors which will automatically pull timing and or add fuel when pinging is detected these gals could be quickly damaged if one is over jealous.
I tend to remain on the safe side of life and tune based on worst case; crappy gas, hot days, a heat soaked motor created as the result of her migrating through and sitting in traffic as such she remains happy and willing to be exercised all the time.
Do I leave a few ponies on the table with this mindset; absolutely however we are always able to drive home and return to play again another day
The best of luck with you quest
Shadowman
