they have a smaller and lighter internal mass which means they waste less power to spin than the 727 depending on who you want to believe it can work out to about 5% less lost power , plus the 904 is built with either a bolt-in or riveted sprag from the factory which is the serious weak point in the 727 -the press fit sprags can come apart and lead to serious failures see the thread in the transmission forum on this-. The guys at TCS Products in Langley sell billet steel or billet alum front drums with a higher snap ring groove to handle 5 heavy red frictions or 6 stock frictions along with a billet alum 24 spring return module and an alum piston which when used with their complete race rebuild kit gives you a 904 that can handle the 1400hp their Comp Eliminator car puts out , Way more power than anything I'm going to make with my stroker but still 5% of 519hp/524tq is21hp/21tq at the rear wheels with the price of adding rwhp why waste what you've got ? I think I paid 7or 8 hundred for everything and did the swap in a couple of hours { the 904 was a healthy working tranny to begin with} ,it was so easy it will make you sick to think what you paid in the past for some clown to do it for you .there's a series of videos on youtube for both the 727 and the 904 that details exactly what to do and the tricks for doing some things that the manual's don't show well worth the time to watch one day when your bored eh lol
