Non-cylindrical pistons?
Non-cylindrical pistons?
(OP)
Does anybody know of any experimentation into using non-circular pistons and bores? For over a century engine designers have relied heavily on the standard cylindrical piston/bore combination. I do know some makers have had experimented briefly with oval pistons (notably Honda's NR engine) but there have been few follow ups.
It would seem that modern day manufacturing techniques would open the door to a wide range of designs that were difficult/impossible to build in the past. So what do you guys think? What are the Pros and Cons of deviating from the norm? Also what other shapes show promise?
Regards,
Bryan Carter
It would seem that modern day manufacturing techniques would open the door to a wide range of designs that were difficult/impossible to build in the past. So what do you guys think? What are the Pros and Cons of deviating from the norm? Also what other shapes show promise?
Regards,
Bryan Carter





RE: Non-cylindrical pistons?
http://not2fast.wryday.com/vw/stuff/1990_2.3d_oval2.jpg
I have no details on the result, but I assume that they didn't like what they saw, as this is the only evidence I have of the project...
I would guess that they had ring seal problems.
RE: Non-cylindrical pistons?
RE: Non-cylindrical pistons?
A rectangular prism would be extremely difficult to design for good sealing and wear.
TTFN
RE: Non-cylindrical pistons?
RE: Non-cylindrical pistons?
As well as being the strongest shape from an internal pressure point of view, a cylinder also has the lowest surface area to volume ratio of any shape that is straight on the walls in one plane, hence it gives the best thermal efficiency, and concequently potentially better fuel efficiency than other shapes
Regards
pat
RE: Non-cylindrical pistons?
RE: Non-cylindrical pistons?
with the racing class rules, the engine would have to be
a 4 cylinder, so the ovaled out an 8 cylinder engine into
a 4 cylinder model, simple as "the mother of invention
is nessesity"
RE: Non-cylindrical pistons?
it wasn't particularly successful against its 2-stroke competition. something about reliability....
the grand prix rules were later updated to prohibit the use of non-circular cylinders.
RE: Non-cylindrical pistons?
PJGD
RE: Non-cylindrical pistons?
it just ain't gonna happen. Looks like it's back to the old
boring round pistons....again.
LOL
RE: Non-cylindrical pistons?
Back in "the olden days" auto parts stores bought pistons in oversize. Then ground them to the desired oversize. At one time I had wone of the piston grinding machines and a set of the different cams. HD motorcycles even had a special cam. Most of what I have read says to measure the piston size just below the rings and perpendicular to the wrist pin. The ring lands are round but progressively smaller than the skirt toward the hotter top, and the skirt area is slightly oval shaped and usually the wrist pin is not in the center either. Find an old piston and measure one paying attention to the power and compression thrust faces, and noticing that unless they are pretty badly worn that the ring lands have never touched the cylinder. A really, really oval cylinder might allow the use of HUGE valves.
Pancholin.
RE: Non-cylindrical pistons?
Yeah, you can do it with NC machinery, but why bother?
Sometimes the old way IS the best way; not everything needs reinvention.