Everyone says to "upgrade" to a TH400 or PG once you get over 1000 HP. Other than the obvious things like the availability of aftermarket SFI cases like the Reid, what makes the GM units better?

Excellent ?....i was just thing the same I would like to think that a 727 will live with 1000 HP but I'm no expert.
Maybe some of the trans gruels will chime in, I'll keep an eye on this thread.

Did a search and found this old thread here it should give you an ideal
https://board.moparts.org/ubbthreads/ubbthreads.php/topics/578024/2.html

Stock TH400 can handle some power if they are properly prepped but they do have there weaknesses with stock componentry like anything else. Where one may consider them better is that they have a stack-shift strategy where on every shift a new clutch pack is engage without having to disengage or have a timed shift. That makes the shift quality superior over a TF727/904 that always have a timed shift and no matter what, you have to deal with some degree of overlap. This is of course no correlation to overall strength.

Just to note some of the mechanical differences. The TF727 has bigger clutches and can run under significantly lower pressures than a TH400. The stock TH400 intermediate sprag or roller clutch(depending on model year and how it was equipped) is a failure point, even with the better 32 element sprag. The TH400 intermediate band is useless in all performance applications and is often removed defeating any compression braking in 2nd. TH400 and TH727 low reveres band are probably about the same capacity based on surface area,

AG.

no expert but, my opinion is your question has the answer in it. lack of aftermarket support and parts. my closest friend has a 727 in a 1500hp procharged duster and works great. no issue for 3 years. the lack of gear ratios is a draw back also. if we could get billet shafts and sfi cases etc. i think the 727 would be the better trans. my 2 cents

I have no comment really on the strength aspect, just always heard they'll handle more power reliably.
The biggest thing I see is gear ratios. Once you make 1,000+ HP (especially on a small tire), you need a lot less starting line ratio. Not many options w/ a 727.

The aftermarket makes it stronger and a better option. The SFI Case is a HUGE bonus.

And the converters are better. There is more room in the chevy style bellhousing for a larger/thicker converter. High hp applications can utilize that.

In my experience up to about 900 hp has been good.The aluminum drum won't come apart. Parts I think are a must at higher power level? A good front drum, steel front planet, good quality valve body, 518 deep pan with a long enough extention to get the filter at the bottom, reinforced band strut, 3.8 or 4.2 lever, solid rod front servo or shimmed solid late servo, lube hole for the sprag. Just took mine down for service as there was a few pieces of low roller clutch spring in the pan at about 250 runs. It does not use no low band apply. It shakes the tires once in awhile, so regular maintenance. New inner race, spring set, and a filter. Ready to go back in service. The band has been in the trans for over 700 passes, the clutches for over 250. In fact the old front clutch frictions and steels were moved to the rear clutch last time around. No metal on the filter either. If you need less 1st gear ratio or a aftermarket case at a higher power level? Then it's time for a 400.
Doug

In stock form I would say a TF727 and a Turbo 400 are about equal - however the aftermarket support for a T400 is a lot more robust than you can get for a TF727 - If You go with an SFI T400 case and all the good billet parts for a T400 a TF727 can not compete at the high HP levels.

Its not a matter of whats stronger, its a matter of whats better supported by the aftermarket. TH400 is like the 9" rear, there are tons of stuff availible , from case to gear sets. When i switched to a t400 the converter was literally 400.00 cheaper. Seriously i priced the same converter for a t400 and a 727,
Best move i ever made becasue there is so many parts availible and the technology of so many people using a t400 now trickles down

I know I know its hard for people to accept but who cares whats stronger, i care about what WORKS the best

Brad Watt (A93demon) still runs a 727 in his demon. He has been in the 4's at 3200? lbs so i would say he making over 1000. He does leave in second gear so that solves the gear issue ,
727 is just as strong as a th400 , but the aftermarket for the th400 is way better, thats really all it is

Totally agree! I tire of the "KEeP iT aLl MopAr" crowd when most of their engine is filled with aftermarket parts anyway!

AS said its more the availability of aftermarket parts. There are many parts out there to make a 727 live at that power level. With a TH400 there are just more options, kinda like a BBC vs a BBM. Both capable of making power one just has many more options. The one thing you cannot get for a 727 is an SFI case, to me that s a big deal. FWIW my 64 Savoy has a 727 built by Joels on Joy, it makes north of 1000hp. From what I've been told torque is the larger issue with a TF than raw HP. The Vette has an A1 built 727 and it makes a tick over 1100hp. They are both very nice pieces but are not a budget friendly one.

I know 3 mopar racers that switched to TH400's and improved et. I don't know if this was due to a better converter or if the TH400 is more efficient? The best improvement in one of those cars was almost 2 tenths, motor and rear was untouched, all mid to low 9 sec cars.
Anyone else had the same result ?

Yours, Chip's, Tony, Al and Doug's experiences are promising. I should be around the 950 hp mark (but unfortunately at 4300 pounds...) in my car once the 540 is done, and am worried about the longetivity of any 727. Figure it needs the parts Doug has listed in it for sure and I'll also move to a LBA valve body, and debating the billet input and output shafts as well. Bummer with the billet output shaft though, it doesn't have the speedo gear provision and I'd hate to lose the speedo on a mostly street car.

The Vette has an A1 built 727 and it makes a tick over 1100hp. They are both very nice pieces but are not a budget friendly one.






Very surprise how was the fit

Since the subject is "stronger", another thing not often mentioned is the case. The TH400 has a "wrap around" case where the 727 is wide open at the bottom...this makes the 727 case more susceptible to flexing under torque and this can affect the internal component's alignment.

how much, if any, does using a deep cast pan on a 727 affect the lower strength of the case ?

Well everythitn gin this car is tight.,Its a shorty version. FWIW we had a TH210(TH400) in the car before the Proflite. It is much quicker with the Proflite hands down not even close. My guess is if someone picked up with a 400 in a non power adder deal they did not have a good work 727 with the right parts for the combo.....