X HEADS

It has been said many times that alloy heads suck heat out of the chambers and so you need to up the Scr about a half a point to compensate, else your car will lose power and lose fuel-efficiency with no other changes.
I can't say if that is correct or not.
But I can tell you that I have run the Eddies up into the range of 185/190psi and more, at full power, full timing, still on 87E10. In my combo this is an Scr of 11 to 11.3, depending on headgasket. So IMO, a half a point is barely adequate compensation.
If your shortblock is already built at some much lower Scr,
AND your car is to be a streeter,
AND it has a manual trans,
then alloy heads might not be the best choice. I mean they are, but the pressure needs to be brought higher, or it will suffer from a soft bottom end, which with a 2.66low gear box.... is pretty much guaranteed to suck.
Thankfully most alloy heads are closed chambers running from 65 to 58 cc, giving you some compression increase, especially over open chamber irons.

IMO
with the price of gas set to skyrocket, we need to build our engines to be as fuel-efficient as possible so we can drive them more than an hour or two on the weekend. High cylinder pressure is the first step.

Your opinion may vary