[Christ]

Piston and bearing friction ARE affected by compression because your analogy fails. There isn't more gravity pushing down on the car when you're going up hill. The gravity goes in the same direction. Instead, increase the weight of your car and tell me that the resistance of the driveline doesn't increase.

Higher compression means a higher cylinder pressure that builds exponentially as the piston rises. A bigger fill [speaking to air density] obviously correlates to higher dynamic compression [DIFFERENT from static compression].

Typically, a higher STATIC compression ratio will increase power output for the same fuel/air charge, provided the increased combustion force is sufficient to defeat the losses of compressing the charge tighter into a smaller space.

Dynamic compression refers not to the relation between cylinder volume at TDC and BDC, but to the relation between actual air charge versus capacity at TDC. Another term is 'volumetric efficiency' and although the two sets of numbers can be used differently, they are similar.

IF your intake valve opens late, for instance, you lower your VE and at the same time, your dynamic compression. The static CR remains the same, but you're putting less air and fuel into the cylinder, so there is less pressure built at TDC and obviously less combustion force [given a complete burn in all instances]. The atkinson cycle design that Toyota uses takes advantage of this principle [and a few others] by leaving the intake valve open late, and thus putting some of the AF mix back into the intake, but at the same time lowering the amount of AF mix to be compressed during that stroke.

In any event, the correlation between intake charge density and bearing load is that higher density = higher pressure on top of the piston which obviously entails higher bearing load.

I briefly touched on this concept in another thread and discussed it with a member [the DIY Warm Air Intake thread], and mentioned a way to do this for a home-modder...

I must point out that at this time, I have NO interest in doing this myself - however, I can help anyone who is wanting to try it out, if there is anyone out there. That said, here is some of the information I remember gathering on the topic; all from memory, as I seldom write down my hare-brained ideas on paper.

A D15 engine from the late 80's to the mid 90's uses a smaller deck height and crank main journal than it's bigger brother, the D16, which is a 1.6 liter 'monster' in terms of efficient engines. IIRC, it also uses smaller rod big-end bearings and an obviously smaller stroke.

My idea was to take a D15 block, bolt the crank girdle on and send it to a machine shop to have it line-bored to accept the D16 crank. While taking measurements, I noticed that there was enough 'meat' there on the caps and block webbing to offset the crank while retaining the same bearing caps and position.

Doing so WILL move the crank centerline closer to one of the main cap bolts than the other, putting a weird stress on the bearing, more than likely.

The D16's longer stroke will compensate for the stroke loss from offsetting a crankshaft while providing a more linear combustion stroke by reducing the arc radius that the rod's big end travels, thus reducing parasitic friction during combustion.

If attempting this, very careful attention must be paid to deck height, rod length, piston crown height, and crank shaft stroke.

For example - doing this ONLY using D15 parts will move the piston down in the bore at TDC and shorten the piston stroke while retaining the same crankshaft's 'stroke' number [the diameter of one full rotation of the rod journal around the main journal]. Thus, doing so with only D15 parts would yield lower static compression ratio and piston stroke length; possibly to the extent that the engine fully assembled would require a deck-adjustment to even start, let alone run efficiently.

The D16 crankshaft has longer stroke than the D15. Some measurement could yield a setup that puts the crown height at TDC the same as the D15's original measurements while retaining the original piston stroke length of the D15 as well.

Small offset should clear the cylinder sleeves and block webbing with no problem... larger offsets may require clearancing similar to the addition of a long-stroke crank or larger rods for performance applications.

In theory, the end result of doing this successfully and retaining OEM operating measurements [piston/deck clearance, stroke length, bore] should gain power and efficiency [through lower frictional losses].

Anyone want to discuss it?