Knocking and the location of detonation

After watching the video about the 4 stroke cycle, knowing that ignition timing comes a bit before TDC I'm curious about one thing. When we advance ignition timing enough, we may start to get knocking. Is it possible to advance ignition timing so much that the detonation is happening before the valve closes? If this is the case, can we swap out cams to prevent this? How does this effect knocking/detonation? By this point, would we already be seeing detonation or is it possible for a more controlled burn to still be taking place even outside of the valve? I would really appreciate an indepth look. Lastly does detonation outside of the valve directly raise likelihood of detonation because we now have flames outside of the area they should be IE the cylinders. Thank you!

Hi Tanner,

Detonation requires pressure to initiate, so it will not happen with the valves open. You can have pre-ignition with the valves open though.

We do not want to have the ignition event occurring that early as it will try and drive the back down the chamber against the upwards force from the crankshaft and con rods. The aim is to have the peak combustion pressure occur around 6~10 degrees ATDC with a smooth curve up to the the peak, and then down again. This will generate the peak load on the piston when the con rod is at the optimal angle on the crank to generate the most torque.

Having the spark event occurring when the inlet valves are open will lead to an explosion/backfire in the inlet manifold, this can cause a lot of damage to the engine.