Hi Cindy ... just to clear up the sprocket thing a little. There is only one RDTH sprocket (690) that will RET cam timing 4* over the conventional (577) RDTH sprocket.
SQTH to RDTH (557) doesn't change cam timing one bit. Got all the sprockets here and have checked.
I won't go into the roller cam differences except to say that TBI are all basically the same (4* RET ground in .. '88 and '89 2.5l only) and then you have the 89+ turbo roller cam which is unique. That's (2) different stock roller cams total.
People can get some nice top end on a turbo with the 90+TBI cams <--- only because they are probably in better shape, then put 4* RET to it. Performs like the '89 turbo cam then ... but with more duration.
SQTH to RDTH (557) doesn't change cam timing one bit. Got all the sprockets here and have checked.
I won't go into the roller cam differences except to say that TBI are all basically the same (4* RET ground in .. '88 and '89 2.5l only) and then you have the 89+ turbo roller cam which is unique. That's (2) different stock roller cams total.
People can get some nice top end on a turbo with the 90+TBI cams <--- only because they are probably in better shape, then put 4* RET to it. Performs like the '89 turbo cam then ... but with more duration.