Just so you know;
the stock 5.9 has more than enough grunt to run any A833 4-speed, with any rear gear, in any A-body; and there are 4 SBM ratios to chose from. ......
and they fit like a glove ......
and on the street, they scoff at 450 ftlbs.....
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As for the ratios;
3.09-1.92-1.40-1.00
2.66-1.91-1.39-1.00
2.47-1.77-1.34-1.00
3.09-1.67-1.00-.73od
As for cruising;
65mph, with 27"tires, by the math;
2.94s=2380; while 3.23s= 2615; and 3.55s =2873
As for taking off;
With a stock flywheel, and a starter gear of 11/1, taking off is a dump-it-and-go deal. By 9/1 or less, there is quite a bit of slipping the clutch going on.
Therefore, the sweet-spot is about 10/1. This would be;
2.47x 4.10, or 2.66x 3.73, or 3.09x 3.23
As for my favorite;
That would be the Commando with 3.55s, but only because she hits 60/65mph at the top of second. She's fine down to 2.94s, the lowest I have tried.
Of note;
1) any ratio can be fit into the A/F-body, alloy box and tail, making it almost as light as the AX. My alloy box survived 4 years of thrashing on the street as a DD, and was still fine when I replaced it with a Passon box..... Over 20 years ago now.
2) if you have bucket-seats, and are replacing the floor anyway, then I highly recommend moving the shifter back, and to the left, and raise it up; then use a short straight shifter. You'll love it. I used a B-body tail and mainshaft, with a home-made(custom-fabricated/lol) shifter mounting-plate.
3) I'll go out on a limb and say this, if your cylinder pressure is;
a paltry 140psi, you'll want a starter gear of ~11.8/1
by 160psi , you'd be fine at 10.4/1
by 180psi, I like 9.2/1
by 195, 8.5/1 is doable
These are the minimums recommended. This is based on my experience over 50 years of driving A-bodies with A833s
I made up this formula ;
1660/cylinder pressure= minimum recommended starter gear.
example;
1660/155psi= 10.7 starter, and
10.7/3.09 trans gear= 3.46 gears;
If you have a 2.66 box then 10.7/2.66=4.02s;
round up or down as may be required.
4) thus it can be seen, the more cylinder pressure your engine cranks, the less it needs for a starter gear.
And the less starter gear it needs, the less cruise gear it can getaway with.
5) to run the overdrive box; the more cylinder pressure your engine develops, the easier it will pull those wide ratios. But the good news is that; with that .73od, you can run almost any rear gear you want to.
And so, I like a final drive of 2.76 ,for 65= 2240(with 27s). This is because, any less rpm will not be able to develop optimum ignition timing.
Thus working the formula backwards, I need 2.76/.73= 3.73 rear gears.
The starter gear is thus 3.73 x3.09= 11.52
If I have a starter of 11.52, then My cylinder pressure can be as low as
1660/11.52= 144psi, about like a stock 318. But, the lo-pressure 318, for performance, will have a hard time with a Second Roadgear of 1.67 x 3.73=6.23 Whereas the 5.9 will find it nearly ideal..... because 65 in Second gear will get you 5040rpm (with 27" tires), which, with the stock cam peaking at around 4400, is just about right.
