I have a set of C90E heads on my car. They have been worked pretty good.They have Hard seats,Solid bronze guides,Manley raceflo 1.94 - 1.60 Stainless valves, studs- guideplates,Dual springs. And a complete port job and the chambers have been CC,ed. There on a 306 c.i.d. bottom end with K.B. .200 domed pistons. The car is a 85 G.T. and has a solid lifter cam,T-5, And a 8.8 with 4.33 gears and a Detroit Locker with 31 spline axles. It weighs 3290 lbs. with me in it and it runs in the 12.50 range at 108-109 m.p.h. The heads work pretty good if they are done right.