Is there a good Dodge overdrive automatic tranny to fit behind a big block? I am gonna build a road car when the AAR is done from a 71 Charger 500 big block car and was gonna put a hgih gear in it so that I can run 80 without twisting the motor so hard. Then I got to wondering if they made a big block OD automatic. I know OD trannies weren't popular until the 80s and I think big blocks were gone by then was there an overlap? Or is a 727 with a lock up convertor the best I can do?

Thanks in advance, Kevin

Popular question. This gets asked a lot.
The sad fact is, the 400 and 440 were gone by 1979. The A-500 transmissions didn't come along until the late 80s in 318 & 360 trucks and vans.
There were no factory built overdrive transmissions with a Mopar big block bell housing.
You can make this work though. The trick is to take a A-500 or a A-518 trans and remove the bell housing, then attach an aftermarket BB bell to the OD trans. Google JW Ultra-Bell.

Thank you, I didn't think so but I figured I'd ask. I'm familiar with the bellhousing option, we ran a glide in a Dart years ago and my brother is building a GTX for a guy with 4l60e (or whatever it is) behind a 540 aluminum Hemi. Will a 500 or 518 hold up behind a moderate big block?

The 500 was essentially a 904 with an add on OD. The 518 was based on the 727 and is the best choice of the 2.
A member here modified a 618 from a diesel truck and "fitted" it in his 70 Cuda. He said with all of the trans tunnel fabrication, he should have just went with a Gear Vendors unit and a traditional 727.

The 360/518 would be your best choice. The 500 was used behind the V6/V8 318S.

I agree a 360 or stroked small block would be the easiest route but it is a BB HP car and I would like to maintain that aspect of it. I figure the torque of a big block should overcome a high gear and still give decent out of the hole performance.

I dissagree. Putting a small block into your B-Body should NEVER be an acceptable option. There are other OD options. A gear venders OD unit seems to be the best option for BB guys. GV units go for around 3k, though. But it beats running around with a little motor.


Not to mention, even with a little motor, you'll have to do some significant floor surgury to get the Chrysler OD trans to fit into an older Charger. So, could the BEST option REALLY be to neuter your Charger with a small block, AND cut the floor all up to do it????

Definitely no floor cutting gonna happen, it is a solid original floor car, not too many of those left.