Gen 6, HP500.
I'm way out of my league here but what are the feelings on flat top pistons? We have discovered in tearing down my motors, that one of my motors was rebuilt last year using FT pistons. I'm trying to match the second motor and FT's are not what we were planning on using. We were going more toward the stock Merc pistons, but these were a bit harder to find. (so I'm being told) I'm not against them, I just don't want the ease of securing FT's being the reason we go this direction.

Also, I'm hearing that the FT's might decrease my compression??? Feedback would be great & remember I'm a novice at this.

It all depnds on the chamber size and shape. You get the wrong pistons for the head and you'll wind up with a bad case of detonation, or worse.
There's nothig wrong with a flat-top. GM used them for years in their engines.
Some 383 SBC's run dished pistons with a small chamber head. The small chamber allows for better quench.

A Flat top piston will have a -3cc eyebrow cut in the top for the intake valve to clear. A 502 piston has the same but the little dome on top brings it up to +1cc. Going to flat tops, all being equal, the compression goes down -4cc. If for say the 502 was to a perfect spec, 8.75 CR, a flat top will be 8.52CR, a loss of 1/4 point compression.

Bore x Bore x Stroke x .7854 = Cylinder displacement

Cylinder displacement x 8 = Engine size

Compression Ratio = ( Cylinder Displacement + Chamber Volume ) / Chamber Volume

This past week I spoke with Jim V. as he was working on my heads. He said that he usually uses a domed piston, but that he would work around the flat top pistons that my engine builder had used.