904 Questions

[RTom]

I am in the process of slowly building a 340 which I am hoping to have in the 450 hp range. While I am a ways away from having it complete, I want to start getting an idea as to what transmission I should be looking for. This will be an auto transmission. This will be going in a 69 Dart GT Convertible if that makes a difference.

Would a 904 be able to handle that horsepower load, or should I be strictly looking for a 727?

If a 904 will work, would a 904 from a 273 bolt right up to my 340?

Thanks for your advice! In all likely hood, I will be rebuilding the trans regardless of what type I get. ( I don't want to spend all this money on a hot 340 just to have the trans be a weak link). Would one be easier to rebuild than the other.

Rich
:cheers:

 

[moper]

The 727 is a shoe in. A stock rebuild with a shift kit and convertor to match will live forever. But, they are heavier and take a bit more power to run it, plus you'll need a new driveshaft as it's longer than a 904. The 904 has a lower first gear which helps a torque limited 340, and it's lighter plus less of a power draw. However, the flaw I hate in 904s is the high gear clutch piston return spring which can uncoil and lose tension with repeated high rpm shifts. That leads to overlap between 2 and 3 and eventual failure. So the fix is to replace the forward clutch retainer with the billet steel replacement that is machined ffor the 727-type spring setup. It also prevents the retainer explosions, and allows more clutch discs and therefore more power transfer capability. If you have to do either, the 727 will be cheaper just because of the clutch retainer.

 

[stroked 340]

904 all the way,properly built will handle anything put in front of it,i've run the one in my duster for 2 seasons of racing behind my 416 and it has been behind my 360 for 2 more, just find a good transmission guy use good quality parts and it'll last, they're lighter then the 727 too..

 

[fishy68]

I agree with the above posts but I notice you also asked about a 904 from a 273 bolting up to your 340. Any 904 from any small block will bolt up to your 340 but the early ones (pre 68) used a small snout torque converter. They'll bolt up but since the snout is the wrong dimension it'll let the converter rock back and forth and break stuff. If your 904 is from a 68 or 69 273 it'll work as is. If not, it wont work without swapping the input shaft to the newer 27 spline shaft to use with the newer converter.