Trans and rear end question

[Cory M]

So...my goal is to get the Gen III 392 hemi in my 72 Satellite, and I'm trying to prioritize a few things. It currently has a 904 trans and 8.25 rear end, and correct me if I'm wrong, but I've heard both a too weak for the new hemi. So, I'm looking at doing the 8.75 rear end, but am a bit stumped on the trans. Which trans would be sufficient and if possible the least amount of headache to get in? I'm leaning toward the 727 small block...but I'm definitely open to hearing pros and cons...and experiences with putting in a more modern trans.

 

[Lefty71]

I don't know much, but I think John Cope makes some sort of super trans for that application.

 

[MoparLeo]

Depends on how much you want to spend. Putting a small block 727 behind it only requires a special flex plate.

 

[Cory M]

Depends on how much you want to spend. Putting a small block 727 behind it only requires a special flex plate.

I'm not opposed to spending a little extra if it's worth it. And I honestly haven't educated myself enough to know the big advantages to the other transmissions...and how difficult they are to get in.

 

[furious70]

Moving up to a 4,5, or 8 spd will be significant money. Double, triple, or more? You get both performance and economy for that money.
My plans include a 727 for a turbo 5.7 race car and the 5 or 8 spd for street car 5.7

 

[Cory M]

Moving up to a 4,5, or 8 spd will be significant money. Double, triple, or more? You get both performance and economy for that money.
My plans include a 727 for a turbo 5.7 race car and the 5 or 8 spd for street car 5.7

I'm not so much worried about the increased cost of the transmission itself. It's the cost to get it in that I'm leary about...the cutting, modification. And does one need a custom driveshaft made to link the modern trans?

 

[Cory M]

I don't know much, but I think John Cope makes some sort of super trans for that application.

I will check this out. Thank you!

 

[RemCharger]

I'm not so much worried about the increased cost of the transmission itself. It's the cost to get it in that I'm leary about...the cutting, modification. And does one need a custom driveshaft made to link the modern trans?

Are you doing these mods yourself or paying a shop?

 

[furious70]

A500/518 won't require much, maybe some hammering. Holley sells the trans cross member set up for the 5/8 spds. You do cut the cross member out with their system and replace with their bolt in deal.
Then another grand to sound German automotive for the controller.

 

[Dave6T4]

Anything other than a 727 is going to mean serious modification to your transmission tunnel. What makes this extra hard is that the torsion bar cross member has to get hacked up. There is a company out there that does an overdrive conversion kit that basically uses an overdrive GM Turbohydro that fits under the existing floor. Even the A518 requires serious surgery, more than hammering. The O.D. chunk interferes with the torsion bar cross member.

 

[HawkRod]

Another option is to use a small block 727 and a Gear Vendor's overdrive. That is what I have done in my 73 Road Runner. In theory, you can split each gear to make the 727 effectively a 6 speed, but I have not found that to be realistic. 90%+ of the time, I simply use it as an overdrive once I get up to highway speed. But it has some controls and you can have it automatically or manually shift itself. So the bottom line is it is flexible in how you use it. If you drag race it, then I have been told shift 1, 2, 2 OD, 3, 3 OD (although the final is likely not needed). I have not drag raced mine so I can't comment on how well this works.
The GV overdrive is not cheap - it costs just under $3000.

As far as installation:

• They will tell you that you only have to minorly dent your transmission tunnel with a ball peen hammer or similar. I found I had to dent it more significantly. However, I did not need to cut or remove anything from my transmission tunnel. I merely gave it a good whack or three and in it went.
• You have to shorten your driveshaft. I found this to be very easy to measure and quick to have done.
• All other items fit in their stock locations. Of course, you need to install the controller inside the car and run a couple of wires, but I did not find that to be a big deal.

A well built 727 should easily be able to handle the power of the Hemi. The GV overdrive can handle 1200 horsepower out of the box, so I think you'll be OK there.

Here is what you get for a 727. The kit is 100% complete and comes with everything you need to install it.

Here it is installed on a 727.

 

[furious70]

The a500 at least requires no surgery, and can be reasonably built to handle the tq of the 392 (think 904 race trans pieces). Depends on what you want to do to the car. A500 also gives lock up.
GV is certainly an option.

 

[Cory M]

Are you doing these mods yourself or paying a shop?

I'd likely be paying a shop for any modifications. I don't believe I have the tool or know how for that kind of work.

 

[MoparLeo]

The 5 speed NAG1 transmissions are plentiful and inexpensive. The 8 speeds used currently are $$$, computer controlled and require major surgery on the trans tunnel and related area.
Really getting a donor post 2015 Challenger would be the ideal candidate. It would have all the little parts that you would need for the swap.

 

[Cory M]

The 5 speed NAG1 transmissions are plentiful and inexpensive. The 8 speeds used currently are $$$, computer controlled and require major surgery on the trans tunnel and related area.
Really getting a donor post 2015 Challenger would be the ideal candidate. It would have all the little parts that you would need for the swap.

 

[Cory M]

The 5 speed NAG1 transmissions are plentiful and inexpensive. The 8 speeds used currently are $$$, computer controlled and require major surgery on the trans tunnel and related area.
Really getting a donor post 2015 Challenger would be the ideal candidate. It would have all the little parts that you would need for the swap.

This is great info. Thank you so much! The nag1 sounds like the ideal compromise.