Quote:
Originally Posted by cr45
If the compression ratio in the "air spring" cylinders were to be lowered I suspect that you might get a useful efficiency gain.
One way to do this might be to remove the inlet or exhaust valves and then block the port downstream from the valve.
Another option would be to fit pistons with a lower piston pin to crown height.
The lower compression ratio would allow one of the compression rings to be removed thus reducing mechanical friction.
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part of the remaining loss would be air leakage, specially in an old engine, effectively the "spring" is stronger on the compression that on the expansion stroke as some air has leaked out. Also, the compressed air at the top of the stroke is hot, and heat is lost there, so on expansion the colder air has less pressure. removing valves to lower compression would help but there is also some increased loss from increased surface area absorbing more heat, and pumping loss.
How about removing rings completely, cut the crown off the piston? this would remove all compression and also lower friction loss as there are no rings and piston friction is also reduced as this is controlled by side thrust due to downward thrust on the crown being translated into side thrust by the angle of the connecting rod.
Ultimately, a smaller engine transplant may be better, like the 3 cyl diesel one on this forum. But I guess this would be cheaper. also consider adding a turbo with this mod to get power back to where it was, you will still get the efficiency gains.