My friend had an '89 Iroc that had the engine replaced with what was said to be an L98 out of a 91 or 92 Firebird Formula or Firehawk. It was for sure an L98 engine. He later bought another '89 Iroc with the orginal L98. Well when we tore both of them apart the so called "Formula" engine had dished 4 valve relief pistons, and the second L98 had flat top 4 valve relief pistons. An Lo5 I had which is the same as an L98 also had the flat tops. Did any L98's come with dished pistons?

My 88 with the L98 does also have flat tops. Could be the earlier engines were dished?

I could be wrong about this, but I think the corvette L98s had 4 valve relief dished pistons in them. This is because of the 58cc aluminum heads they came with to keep the compression at 9.3 to 1. I've taken apart several iron headed (camaro/firebird) L98's and they have all had 4 vr flattops in them. However, I have never dug into a vette spec L98...so I dont know that my info was 100% accurate...