 The initial intake valve timing was changed in 1973 (EPA mandated) from a longer duration to a milder duration, this and other changes stifled the later models somewhat, the compression ratio also became lower over the years to match the milder cam timing, the flywheel is lighter than British contemporaries, this has the effect that the engine tends to pick up revs more rapidly when the throttle is opened quickly.During the later developments of the engine compression ratios were lowered, then raised.Pistons were lightened 20 percent along with connecting rods to reduce the reciprocating mass inside the engine.