To my knowledge, the 1985 roller engine did not have forged pistons. I believe it had dished cast pistons. You certainly don't want a 1986 if you're gonna try to use the stock pistons. 1986 did have forged pistons, but they are flat top and do not have valve reliefs. The 1986 engine will require a piston change to run anything more aggressive than the 1987-1995 stock HO heads. You will also not be able to cam the 1986.
If you're trying to find the most versatile roller cam engine, the 1987-1992 should be your selection.
They had forged pistons with valve reliefs and the roller cam.
The GT40 heads can only be found on the 1993-1995 Cobra, and the 1993-1995 Lightning, to the best of my knowledge. Your chances of finding a set in the junkyard are slim to none, and if you did, they'd cost you a pretty penny.
The GT40P heads flow better than the original GT40 Cobra heads. Dispite the smaller exhaust valve size, a better port design. and the removal of most of the exhaust thermactor valve bump allows the P heads to flow better. About 195cfm intake/140cfm exhaust at .500. They also have a smaller combustion chamber size than stock or GT40 heads allowing for higher compression. The GT40P heads will give you about 9.5:1 CR on a stock 1987-1995 engine, and the GT40's will drop it to about 8.8:1. Between the two, the P heads are better, and they generally cost less. About $500/pr assembled. Both types of GT40's are iron.
The GT40 series heads are not as aggressive in flow as aftermarket aluminum heads.
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