[Dinsdale]

You would still need rings (assuming you want compression).

Engines today ride on the rings, the piston should not touch the walls (or you got problems).

The rings are spring loaded outward which is why you need a ring compressor to assemble.

The best a maglev piston could do is decrease the variability of the forces on the rings, perhaps allowing you to use rings with a lower spring constant.

Selinoid valves are thought to be the next big thing in F1, currently they use computer controlled phneumatically actuated valves. My bet is when the next breakthrough comes it will be from racing. Racing saves fuel.

[mamelukesabre]

Engines today ride on the rings, the piston should not touch the walls (or you got problems).

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What exactly do you think a piston skirt is for??

[John Jamieson]

The piston does ride on the wall. On a film of oil. Rings cannot hold them off.

[boris]

"Selinoid valves"

Solenoid.