Maximum HP in 904 Transmission With the following parts:

Hi friends,

Initially when JoeDust451 called me, I thought he was talking about a 727. I wouldn't really recommend a stock 904 be used behind 600hp. The 727 is a different story, however.

It all depends on how much power you make, the weight of the vehicle, and what your goals are with the car.

I mainly build 9-10 second 727's that bracket race at 6000 feet elevation. That unit we build is good for a minimum of 300 runs before a freshening.

The 904 on the other hand, is also very good. But it does need some upgrading. As mentioned, the high piston spring should be upgraded to the multi-spring design. Besides that we typically use red clutches and bands, and a low gear set to get these cars moving quicker. Heavier lower powered cars greatly benefit from the low gear set in a 904 or 727.

I DO only recommend and install valve bodies that apply the low/reverse band in first. I won't sell a valve body that doesn't. The pictures in the exploding torqueflite thread are all non-low band apply valve bodies. You need to be very careful in 1st gear regardless of which valve body you use.

With JoeDust's app, I recommended that he go ahead and install the 100 shot with no worries or upgrades needed to his current 904. If the transmission was in my shop, we usually upgrade them all the same to prevent a failure. Meaning, we over-build the transmission so you have room to grow. Most folks want to add more power later, etc.

Thanks for reading,

Chris Andrews