High comp piston vs. timing advance for reliability

[alping45]

I have an '07 400ex and was thinking of putting in a $20 sparks 6 degree timing advance key as a cheap alternative to a high comp piston.But as I got thinking about it, the key would cause the flame front(explosion) to start pushing down on the piston sooner, meaning that the crank would be at a more vertical angle, creating more stress(wear) on the rod and bearings), right?
Whereas with a high comp piston the explosion occurs at the same angle as stock when the crank angle is not as steep just at a higher pressure.
So, am I missing any aspects of the high comp piston that would cause any more stress than advancing the timing? They both create more pressure, just at different crank postions.
Am I right or not?


And I am also still trying to debate which would cause more heat, the flame starting earlier and getting compressed for a longer period of time when advancing timing, or the high comp piston creating as much or more pressure(pressure = heat) on the compression stroke.
Any thoughts?

[bearair]

Your reasoning is off just a bit. Higher compression means higher cylinder pressure when the mixture is lit. This leads to a flame front that propogates faster and puts a higher pressure on the piston to move it down the cylinder.

Advancing the timing on a lower compression engine works slightly differently. The mixture isn't compressed to the same degree when it's lit, so the pressure builds slower. Some of the energy is wasted as the burning gases expand past the point where they are putting as much pressure on the piston due to the increasing volume of the cylinder as the piston moves down. By lighting it off sooner, you get the maximum amount of pressure on the downward stroke that can be gotten for the compression. That's one of the reasons that you can't use the timing key past a certain point compression wise. If you use too much timing with higher compression, you get a flame front that builds faster that is also coming earlier in the cycle. This can cause pressures to spike too close to TDC and power is wasted. Dropping the timing back a few degrees with higher compression puts the maximum expansion of the gases at the proper point in the cycle so that the maximum amount of pressure in the cylinder can act on the piston for the maximum amount of time.

I just called Curtis Sparks and I wanted to clarify this with everyone... YOU CAN run the key with 11:1 or 10:1 pistons. High compression is considered to be 12.5:1. So you can get even more so of a gain with a higher compression piston.