The 518 can in no way rob more HP than a GV. The 518 only adds roteing weight in 1st 2nd and 3rd, no other "drag" is added, the pump is not doing any work holding clutches or bands or line preasure or any thing. The GV adds a similar amount of rotateing weight in all gears combined with an almost useless extra gear. The OD section can easily have clutches added, if you use the 48RE OD section it can handle 800 lbs tq easily!

As for the 1 second difference in ET from a 727 to a 518 I say BULL CRAP! Like I mentioned earlier, there is a few pounds added to the rotateing weight, thats IT! In first second and third there is some extra weight and in no way can those few extra pounds knock off 1 second in ET. If the trannys get equal prep it can't be more than a couple tenths. If 5-10 pounds in rotateing weight could really knock off 1 second then every car could switch from a steel drive shaft to carbon fibre and gain a second