I read somewhere that they close the intake and exhaust valves, so the air in the combustion chamber is compressed, then releases some of its compression energy back to the piston to help reduce pumping losses.

Bill Schertz
KIS Cruiser # 4045

Bill,

 You have it correct. The explanation I got was most of the loss in compression is recovered in expansion. (rather than combustion)  A compression release is not the answer as engine braking is caused by compression release. It is also noisy, the jake brake used on diesels is a compression release, though the diesel is louder due to it's much higher compression.

Bill Jepson