Paul_VR6 wrote:Best torque may or may not be near knock. A lot of variables are at play. The more compression, boost, earlier exh valve closing, heat, etc the closer they will probably be. I have tuned engines where taking timing out increased power, or kept it flat. Always run the least you need for best torque.
Yes, as I mentioned pressure and heat before.
However, if the engine was borderline on knock before it will run better on higher octane.
The objective is pressure building up above the piston. The more pressure you can build before it self ignites , the more torque you will get. No arguing about that I would think.
Oh, I can argue with that! It all depends on when in the crank rotation the "more pressure" occurs. Max combustion pressure does not determine torque output. Toque is a complex mathematical integration of the torque throughout the engine's two crank rotations of a cycle. The instantaneous values for pressure, connecting-rod angle, and probably others have to summarized to determine the engine's torque output. Remember, any pressure before TDC results in negative work, we put up with that to get the best amount of positive work in the combustion (expansion) stroke.
Main force comes from pressure above the piston. The objective is to have as much pressure as possible when the crank and piston are at 90° angles. What you said doesn't change anything from what I've said about ignition and pressure.
If you have the main pressure arrive at 50° ATDC your pressure will be lot lower since the volume above the piston has increased. The total pressure to push the crank will therefor create a lot less force.
The intent is to have the pressure peak at around 17-20° ATDC. At that point ca. 50% of the mixture is burnt. The remainder is burnt during the rest of the downward stroke to about 90°. The still burning remainder creates pressure roughly keeping the exerted force on the piston equal during that remaining 70°/