seem to be getting some contraversy here....some people say dont load the engine too much and others say keep the revs as low as you can regardless of load.... anymore opinions?

 

Engines are more prone to detonation at low rpms. It's straight physics. The A/F mix will detonate once it reaches it's self ignition temperature. This can be through a pressure increase (higher compression/more boost) or through radiant/conductive heating. Combustion is actually a slow, controlled burn (compared to an explosion). It starts at the sparkplug, and the flame front travels across the cylinder. Meanwhile, the cylinder pressure is rising because the burned gasses are expanding, and the temperature is also rising since the pressure has increased, but *also* since the radiation from burning gasses are heating the unburned A/F mix. Think of facing a bonfire. Your face is hot, but your back is cold. At slow rpms, the mixture has much more time to get pre-heated, so it's closer to its self ignition temperature by the time the flame front slowly travels to it. Another factor is that the flame front speed is proportional to the rpms - higher rpms = faster flame front speed, which is why you don't have to change timing by orders of magnitude w/ rpms. If the mix reaches the self ignition point before the flamefront gets to it, the mixture burns all at once (explodes), which creates a huge pressure spike and breaks things.

Ways to prevent it - less timing: The burn starts later, so you've got less time the mix is exposed to heat & less cylinder pressure at that instant, so lower mix temperatures.

Lower compression/less boost - lower pressures = lower temperatures

Intercooler/Cold night = lower temps starting out

More fuel = colder temps since the fuel takes energy to get heated prior to burning (WAG here)

Tighter Quench = faster flame front travel and/or shorter flame front travel distance. A flame front can't travel in the .040 crack between the piston and head because the piston/head surface takes all the heat away & flame doesn't have enough energy left to sustain a burn there. The tighter quench also squishes more mix into the main chamber, for more tumble & air motion.

Smaller bore = less travel distance so the burn is finished sooner, therefore less time for the end mix to get preheated.

Moral of the story - let the flame front burn everything in control, rather than have detonation.