Consider the simulation I ran with a predictive combustion model. Though it's just a simple 4-cylinder model, the same applies for all gas engines. Spark timing has been varied from -18 to -10 degrees. a/f ratio is the same throughout. you may be wondering why the peak power does not go up much. recall from your thermodynamics class that the integral of the PV diagram is the actual work produced by a heat engine. timing increases power by pushing the peak in the corner higher and higher. boost adds power by shifting the entire curve upward.
of course every engine is different, but the principle of how timing adds power is the same. Every car will continue to add power up to a point, at which point the car will begin to lose power as the burn rate happens too quickly before TDC. Of course, the takeaway message here is that even before this point, you're building power at the expense of cylinder pressure (as seen in the P-V diagram). not a good way to build power when you have concerns about lifting the heads.
this is why i cringe when people use the stock ECU without an ITC or emanage to pull back timing. the factory timing is just way too advanced for anything other than a overspun turbo or n/a engine. choosing the right injector size doesn't change this fact, since the entire map, even the "meaty" part is way advanced.
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