If I understand your post, you are right. First, no explosion. Remember fuel burns, not explodes. Compression ratio has a lot to due with when the spark will actually be triggered. A lower compression ratio usually tends to have higher spark timing. More compression leads to a greater risk of detonation. Octane rating also has a lot to do with detonation. When the pressures get to high, it can lead to detonation(explosion of fuel). Lower octanes tend to burn faster than higher octanes. And the ignition timing usually isn't fixed, usually. If you tried to start an engine at 30 deg. BTDC(before top dead center), it would be extreamly hard to start. Usually ign. timing is about 8-12 deg before TDC at lower RPM's(when starting). 30 deg is a very general statement. A normal combustion cycle doesn't want to stop an engine dead in it's tracks. The pressure builds untill it reaches it max just as the piston reaches TDC (top dead center), and forces the piston back down. Detonation will try to stop the engine dead in it's tracks, and is sometimes sucessful. "
Just wanted to clarify here. But I also wanted to say your posts were very well written and informative. The timing and Octane numbers you gave are very specific to automotive engines. The octane ratings in Aircraft fuels use a different rating system than normal auto gas. Another thing you need to keep an eye on is that AVGAS is Leaded, and the "Gunked Up" plugs that you are hearing about is from lead fouling which will bridge the gap between the electrodes and prevent a spark. When a customer brings in a "rough' engine, that is usually our first Suspect, which is caused by running a rich engine. 80% of the time we clear it up by running the engine at full power and leaning for peak EGT for about 5 minutes or so to clear the plugs, if that doesn't work we typically pull and clean the plugs before suspecting other problems.
In most Recip Aircraft engines the compressions are lower and therefore have different Timing than Automotive engines. So the original statement of about 30 degrees BTDC is far more accurate than 8-12 degrees. Now the timing is dependant on the engine manufacturer and configuration and certified fuel; but it is typically between 23-28 degrees BTDC. Most aircraft engines, with the exception of the Turbo Diesels, all have fixed timing once the engine is started. On start-up the magneto's impulse compling serves 2 purposes, one to accelerate the magneto to provide a stronger spark, and 2, to retard the timing to nearly 0 degrees BTDC.
Now for my $.02 about the LOP or ROP discussion. In Aviation Engines you want to run slightly ROP, Unlike Automotive Gas, AVGAS has some small lubricating properties, but like the previous poster said, you run too much fuel in the cylinder you will "wash" the cylinder walls, but Aviation engines still rely on the Gas for partial cooling and partial lubrication of the cylinder. And as soon as you start running LOP, you start starving the engine and losing power, very bad thing in aviation. Thats my 2 cents, but now for the legal requirements of my A&P.... Consult your POH for the final say.
Edit: Figured I should give you some background so you know I actually know a little about some things.
Been an A&P for over 10 years. 6.5 years Working on Jets, factory trained on CFM-56, CF-6, CF-34 engines, 737s 767s, 707s, and CRJs. 4 years as a GA mechanic working on Cessnas Pipers, Beech, Cirrus, and Diamond aircraft. Factory trained and certified on Lycomings, Continentals and Theilert engines. Did the GA stint to help pay for a small part of my Aerospace Engineering Degree at Embry-Riddle.
