Rebuild 904 or swap for 727?
The 904 fans defend their tranny vehemently, but 727 guys generally just keep their mouth shut. The 727 is the trans that is consistently tested behind thousands of horsepower. Rarely do you see a 904 in that position. WHY? BECAUSE THEY DON'T FIT A BIG BLOCK. Catastrophic breakage in a 727 is common because they are subjected to twice the horsepower than the 904; and on a regular basis. Is a hemi owner going to try a 904 behind his 1,200 horse motor? He would laugh you off the track. If you wanna feel good about your lil 904, then more power to ya, but they're just like C4s; builders love them cuz they're making money off them; not cuz they're good transmissions. Builders can't make the big bucks off a 727 cuz they're just aren't enough customers. I myself have a built 904 behind a mild 360 in my 66 Dart, but if I had a 408 I'd modify the floor and firewall and run a 727. Running a 904 to get an extra fifth of a second in the quarter is the only good reason; otherwise you're just buying into the scam and spending a ton of money on something that will never be comparable to a 727. The folks who understand this won't chime in cuz they don't want to be attacked (and misquoted) by the fanatical horde. Do yourself a favor, don't buy into the 904 hype and just run a 727 if you can.
I don't think you are reading some of the other posts.
It was already said that Pro trans specializes in installing 904 internals in 727 cases that fit big blocks. They do it all the time.
But those trans don't need to last 100,000 miles either. But in most applications they are not breaking all the time either.
In an interview on YouTube with Leah Pritchett who drives a high 6 second challenger she was asked why they are using a turbo 400 trans in a dodge. Her answer was there is no Sfi 727 case that can reliably take that much horsepower.
No one has disputed that a 727 is not stronger and more durable, no one. It is you that continues to make statements that defy logic
That a heavier transmission can go just as fast in the quarter mile as one that is much lighter all other things being equal. It can't.
Weight slows things down, whether it's spinning wheels, tubes in your slicks, a heavier car, or yes a heavier transmission.
The 904 internal parts are very popular in a pro trans 727 and soon a turbo 350 because the design walks the fine line between lightweight and reasonable strength. You can never build a fast car overbuilding everything with brute strength excessively heavy parts.
Roller clutch failure and the subsequent possible drum explosions
Are not necessarily caused by horsepower. The ones I have seen have almost all been relatively low powered cars doing there burnout in first gear. Misuse. Improper valve body.
In a very popular 727 book written by Carl Monroe, it states that a stock 727 case is reliable till about 800 horse. Are there guys who put more through them sure, but they are probably very light cars.
1200 horse cars usually have aftermarket turbo 400 cases that can reliably take that kind of power. So again I say build a trans for its intended use. No performance 727 should use a stock drum.
It's not a weakness, it's the material that Chrysler made those drum from and weight of them that causes them to explode when revved past there design limitation. So again how can you build a 727 for 1,000 hp reliably and safely for say $500.00. You can't.
The 904 is plenty strong for the average guy.
