1.7 or 1.6 rockers

the 1.7s are going to apply more lift to your setup, and the gt40s are already setup for pedistal style rockers....if you went stud, you would have to have the heads studed

i got mine for $66 used. mine came off a cobra. 1.7 ped mount 5/16. are the aluminum heads ped mount also ?

whats the formula for calclating lift with different rockers?

The lobe lift of the cam is increased by the ratio of the rocker arm to produce the final amount of valve lift. A cam with a .320" lobe lift using a 1.50:1 ratio rocker arm will have a .480" valve lift (.320" x 1.50 = .480"). If you install rocker arms with an increased ratio of 1.60:1, with the same cam, the lift would increase to .512" (.320" x 1.60 = .512"). The engine reacts to the movement of the valve. It doesn't know how the increased lift was generated. It responds the same way it would as if a slightly larger lift cam had been installed. In fact, since the speed of the valve is increased with the higher rocker arm ratio, the engine thinks it has also gained 2° to 4° of camshaft duration.

The stock roller rockers on an 87-93 5.0 are rated at 1.6:1, however, testing has shown that these stock rockers tend to flex, and can actually be anywhere in the range of 1.46:1 to 1.66:1. This is why even an aftermarket set of the same ratio rockers can be more helpful already, but also adding some 1.72:1 rockers will definitely bring more lift out of your cam. Just do some research on what cam you are using and how much lift will work with your pistons without having any clearance issues. Once you know the specs of your cam, and which rr's you will use, you will easily be able to figure out how close to the limit you can come without creating too much lift. The formula above should help out.

most aluminum heads are set up for stud mount

The Ford Racing X303 and Y303 heads are likely set up for pedestals unless they've been altered.

To calculate the change in ratio if you don't know the peak lobe lift, just multiply the peak valve lift with the known ratio, by the ratio of ratios. Clear? The E cam has .498" valve lift with stock 1.6's. To calculate the new peak valve lift multiply .498 X (1.7/1.6) = .529" peak valve lift.

You should check p to v clearance with those heads and that cam -- you'll probably have plenty of clearance. Minimums of .08-.10" intake; and .10"-.125" exhaust clearance.

Lastly --- if this stuff is going on your 87, and it's still speed density, it's probably not gonna like that cam very much...

BTW - which GT40 aluminum heads - Y303, X303 or Z303? If by some stretch you're going with the new bigger-valve Z heads - DEFINITELY check p to v...