904 vs 727?
How many times do we have to have this discussion? You're obviously not going to be happy until you swap to the 904, so do it.
not quite. I've dealt with both of these trannys over the years// both personally, (I am 54 and have yet to own any other brand of vehicle than Mopar) and in my living turning wrenches. Personally, I have heard many brag about how great a 904 is// yet I cant seem to get the life out of them behind a stock 318... driving how ~80% would call "normal" driving. I know either can be "built up".
and the decision at the assembly line level, as to which vehicles got which tranny is confusing. 904s in something like a 3/4 ton van with a 360, that gets USED as a van, or in a late 70s B body wagon, never made sense to me. and here i have a "lightest of the light duty bare bones pickup" that a few years earlier would have been called a "MISER" package, with a /6, with a 727.
I have said this before, but sometimes I post things for the "good" of others"> Rusty and me had talked about this subject a while back, in a different thread.
I thought it might be good in a more appropriate section ("tranny and drivetrain") as a standalone question.
alot of good points have been brought up. like the "blocking off of the lockup" in those years, when they presented issues. Id like someone to expand on that. If only for possible red flags to beware of, next time I pull the pan. Like how to "undo" what was done, if I so decide.
also the rear drum explosion thing.... common sense would say that the bigger heavier built parts would be thought to "hold up" better.
But I'd like someone that could xpand on 1 thing (at least) the "IF a 904 eats 12% of engine power, a 727 will eat 18%". is this a hard and fast rule? are those accurate numbers? or pulled out of the air? Do all 727s eat half again, as much power to run vs a 904?
Has anyone (or would it be possible) to somehow dyno a 904, and then run a 727 on same dyno, and measure power consumption? I cant be the only one who'd be interested in that sort of info.
Is there a set HP number it takes to run either trans, before the rear wheels get "any" power, to push the car ahead?
Granted, I know this would be impossible due to bellhousing bolt pattern differences/ but, suppose for a minute, that the same Mopar 3 speed auto, "could" bolt up to a /6, or small block, or big block. We're using same converter. What HP does each trans take to run?
pressures are the same, inertia is the same, pump load is the same, if it takes (lets say, number pulled from air) 30HP to run a 727 behind a /6, then it should take the same 30HP, to run the same 727, behind a 500hp big block. The percentage of power loss to the trans would be less with the bigger engine, 100hp /6, divide by 30 hp to run the trans is 30% of available engine power. while 500 divide by 30, is (guessing) about 7-1/2% of available power. but still 30HP. (or whatever the real number is)
What effect does stall speed have, on power eaten by a given trans? This is before gearing, cams, manifolds, various carb differences, aerodynamics, etc comes into play. how bout billet accumulators and servos vs factory plastic ones? or various trans mods?
Inquiring minds want to know.
