I've been comparing gt40 and gt40p heads. I'm pretty much going to grab whichever one I can from my local junkyard, understanding I'll need new headers for the GT40P. I'll probably get the GT40P, because they make more power, but my question is, I know the lower combustion chamber will increase the compression ratio. My question is by how much will it increase. I'm currently running a B 303 cam on stock heads with a few other things, but nothing to increase compression ratio. I'm currently running 87 and would not like to have to run any higher because I graduated college, am currently in grad school, and I'm paying back my undergrad. Does anyone know how much higher the compression ratio becomes when you run GT40P heads, and is it enough to force you to runner a higher octane fuel? Thanks.