20+ years of "Building 904/727 for drag racing use"
In reading all of this information, I have a few questions!
Between the 904 & 727, there comes a point where parts, for ether, become limited. Between the two;
Which one would be the better choice for a 9 second ET car.
(In my case, it would currently be a small block Duster being built.)
Ultimately, which one can hold more power?
Where are their respective Tq. & HP limits?
It gets to the point where you forget both the 904 and the 727 and get a TH400. The case becomes the weak link and AFAIK no one is making an aftermarket 727 case.
I have an 8 second car that I run a 727 in with no issues, trans brake. My father and close friend have 3350+ lb B-body cars that run low 9s and both run the 727 with no issues, footbrake. I know DVW runs 8.90s on a 727 with a 3300+ lb B-body car. Another close friend of mine we are putting a 572 wedge in his Roadrunner next month that will hopefully weigh between 3300-3400lbs. 727 in that car as well, with a trans brake.
I am not saying the TH400 isn't a good alternative for a 3 speed because of the aftermarket case, but me personally I do not see the 727 case become an issue unless someone sends a stock front drum through it after a sprag failure. I am sure Duster346 can comment further on this regarding the torque and HP limits being that he has been doing 727s a lot longer than I have. However, when converting to a TH400, there will be a lot more money spent due to needing a different converter, shifter, etc.
rumblefish, I would say the 727 should suit your needs just fine. I am sure there are plenty on here that will say the 904 will work fine as well. I know I personally have seen many of 727s go down the track running in the 9s (Typically in B-bodies) with nothing more than a Cheetah old school RMVB, 4.2 or 5.0 lever, good front band, and 12 element bolt in sprag. In my opinion, for what you want to do, I would say a good front drum, good bolt in sprag (6 bolt 16 element), low band apply valve body, steel front planetery carrier, deep pan, billet low/reverse servo, rear roller support, hardened pump gears, 4.2 lever, should last plenty long in a small block A body that runs 9s. You can do more upgrades but I think you would be fine with the ones I listed. I hope Duster346 and other experienced builders would agree.