I took off the heads today. I was told that they were dished pistons by someone on the board..

But, my brother said they weren't dished pistons, I forget what he said they were.

The have 4 separate groove marks on them, 2 in a line, kind of hard to explain, but I'm sure some of you may know what I'm talking about.

so, anyone know?

 

Is there a ridge that's raised up around the outside, like all the way around? If so, it's considered dished. If not, then it's a flat top.

The grooves are valve reliefs. They're put there to make sure there's not any valve/piston contact, and they actually help to unshroud the valve when they're open and the piston's close to them.

If there's a raised part anywhere on the piston, it's usually considered dome top. I've seen some that are only raised just in the middle, like right behind the valve relief, but they're still considered dome top.

MOST factory cast pistons are dished, even if only a little. Like I said, if they have a little 'step up' around the outside edge, they're dished.

AJ

 

Hmm, I'll take a look tomorrow. thanks

 

If it has 4 valve reliefs they are most likely flat-tops.

 

Just about every piston I've seen out of a stock engine (which Mark's is a GM Good Wrench crate motor) had 4 valve reliefs. They do this to speed production. If there were only 2 reliefs, then each piston would have a dedicated side, and in GM's eyes, that takes too much time to do while putting them together.

AJ

 

i got dished.

 

Want me to 'dish' you up some flat tops?

AJ

 

I saw your pics Mark, i didn't know they made dished with valve reliefs.