Depending on your torque output, and specific build;
the A/F body A833od unit, a 3+1, is a great option.
What I mean is this;
the ratios spreads are a little wide, and better suited to engines with a broad flat torque curve. Like low-compression factory engines.
As you put more and more cam into your smaller displacement engines, generally, they trade away low-rpm torque to get the high-rpm power. and soon the holes in the gear-splits become evident.
This is the same for the Passon 3+1;
the difference is that the Passon will embrace more torque.
In a small-tire street car like a Dart or Scamp, etc, this is sorta moot.
As for a big-tub car like a Duster/Demon/Barracuda, I drove those boxes for more than 5 years, and the only thing my hi-torque 367 ever broke was that puny overdrive gear, and that was my mistake, every time.
But if you have a hi-compression BB STREETER, I fail to see an advantage of having anything more than an overdrive 3+1, anyway.
If your looking for fuel economy with a cammed up BB, the slower you run them the less fuel economy they are likely to return. This is because as the rpm goes down, it becomes increasingly difficult to give them the timing they want, with the factory-style ignition system.
So then, in my struggles with my 367, I found the magic window at around 2200 rpm. Well, that requires a final-drive ratio of ~2.76s. That's a tuff number for a 367, to be sure, but with a 3.09 Commando low gear, that becomes the same starter gear as 3.23s with the standard 2.66 box, or 3.55s with the 2.47 box. So, it's just doable.
With a BB then, I imagine, the combination of 2.76s and a 2.66 box, would easily be doable, on the street. BTW Street is all I know.
Now with BB torque on tap, the 3+1 , for a final drive of 2.76, we can use 3.73s, and the starter gear becomes 11.52, which is sorta ridiculously low for a BB, but Second gear is where the action is anyway. So then with 3.73s in the back, Second Roadgear becomes 6.23, a pretty good number for a BB. (my 3.67 likes 6.20 to 6.80)
Lemme stack some numbers for you.
First lets look at the relationship of rear gear to cruise rpm with 27" tires.
2.76 = 2234rpm times .73od = 2.01/1630rpm
2.94 = 2380rpm times .73od = 2.15/1737
3.23 = 2614rpm times .73od = 2.36/1908
3.55 = 2873rpm times .73od = 2.59/2097
3.73 = 3019rpm times .73od = 2.72/2204
Next the transmissions in question;
3.09-1.67-1.00-.73od splits; .54-.60-.73
3.09-1.92-1.40-1.00 splits of .62-.73-.71
2.66-1.92-1.40-1.00 splits of .72-.73-.71
2.47-1.77-1.34-1.00 splits of .72-.76-.75
Pick a cruise rpm, which will pick the gear for you. Multiply that gear by the transmission ratios, to get the Roadgrears
Ok here are some examples
Here is the Mopar 3+1 with 3.73s the roadgears are;
11.52- 6.20-3.73-2.72 and 65= 2200 with 27" tires. Note the 6.20 Second gear, which, as mentioned, is a pretty good Second gear. This will get you 65mph at about 5000 rpm. To get to that number with a regular 4-speed requires a rear gear of 3.23s and the Roadgears become;
8.59-6.20-4.52-3.23 and 65= ~2600 IMO, a stout BB could easily pull a lil less Second Gear, and lets put a Commando 4-speed in front of it, and so the Roadgears are;
9.08-5.64-4.12-2.94 and 65= ~2400 MY Opinion is that this would be pretty sweet with a stout BB.
But if fuel economy is not your concern, then put me on ignore, lol
