Hey guy been doing a lot of research and iv gotten a lot of different answers so i'm here to get a correct answer. This is what i believe to be correct. Pre 87 compression was 8.4:1 post 87 factory flattops made it around 9.0-9.1:1. I bought a 1990 5.0 and the guy said it was rebuilt and had aftermarket flat top hypers that made it 11:1 with stock heads and ultradyne cam. That seems crazy because i thought it would be the same because from the factory they were flat top already. Is this right? could the aftermarket ones be taller or something or are there other factors that could raise it?