[ZOOKER]

You mean like the old 2-stroke "rotary valve"? Maybe.

OTOH, with electronic or computer-controlled valves, you could drop a few cylinders on the engine to zero compression, limiting engine displacement to only what's needed (problem 2).

Like the old Cadillac V8-6-4 engine, except make it work RIGHT this time...

[John Jamieson]

You always have all the friction of the big engine plus pumping loses. GM is going to try it again, I understand.

I built at two cylinder out of a 4 cyclinder Opel in the 70's. Top speed 55, but mpg went from 30 to 40. Research shows about 3% efficiency increase per 10% displacement decrease.

[Redcloak]

That's the other option that came to mind. Ditch the cam shaft and use electrically actuated valves. You could then keep the exhaust valve open during the start of the compression stroke to keep the ratio down. At the right point in the stroke, close the valve and inject the fuel. Computer controlling the valves would allow variable compression ratios depending on engine load. A computer controller would also allow better use of pressure sensors. You could know what the compression really is rather than estimating it based on engine geometry.

[FreePaul]

Like the old Cadillac V8-6-4 engine, except make it work RIGHT this time...

Now you have really thrown out a challenge to "Detroit". I always thought of it as the 2, 4, 6, 8 but that is probably extreme.