anyone care to explain this piston?

[vagassasson]

Why does the piston on the right have a big hole in the side that goes almost all the way to the middle. It has the same hole on both sides. I am new to working on k5 motors so if this is a really stupid question just delete this thread.

[vagassasson]

It also has a set of groves machined in the ring area of the piston

[stujordan]

Holes I guess are for cooling....

Grooves r for the rings?

[Motorrad]

Holes for weight

Groves?

[vagassasson]

If you zoom in really close to the rings on the right there are 5 small groves cut in between the ring groves and 5 more above the ring groves +1 more below the ring groves

[vagassasson]

Factory piston
other piston

[stujordan]

Id wager they are for trapping oil and hot gases....think of them as built in micro-rings....anyone got a better guess?

[vagassasson]

Id wager they are for trapping oil and hot gases....think of them as built in micro-rings....anyone got a better guess?

I was thinking the same thing but I had never seen a piston like it before so I had to ask

[stujordan]

Are u going to a larger bore or just replacing the piston?

What brand is that piston?

[vagassasson]

I bought a used piston and cylinder off eBay.  This is the piston that came with the cylinder but as you can see its already pretty wore out

[Speedway73]

Piston on the right looks like an older Wiseco. The tiny grooves were marketed as "anti-detonation" grooves I believe.