The od box has ratios of
3.09-1.67-1.00-.73, compared to an old 3
speed of IIRC
2.95-1.70-1.00 compared to an A833 of
2.66-1.92-1.40-1.00.
No matter which one you choose, it will be very important to put the engine rpm in a sweetspot in second gear, cuz in the city, that is where your engine will spend most of it's life. If the engine rpm is so high that you find yourself grabbing third all the time, then you will back and forth shifting a lot of the time. If course, with the od box, third gear is direct, so dogsville.
But if you find yourself looking for first gear all the time, then with the od box, the engine will be screaming in first gear; so now yur stuck in a terrible situation. It might not be quite as bad as I make it sound, but I finally yanked mine out after trying it for two or more summers, with a V8, with many a different rearend ratio.
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But consider this; with A833/3.23s, your starter gear, the gear you start off with, will be 8.59, and 9.98 with the od box/3.23. That is a 16% boost. With the 8.59 you will need a lot more clutch slipping to get moving.
Now consider that at 2000 rpm your engine might be making 130 ftlbs of torque at WOT, I mean just guessing
And say you have 24" tall tires. And say you found a nice A833. Then to the pavement, your slanty will put;
130 x2.66x3.23x24/24=1120 ftlbs at WOT! .
What about with the A904? the ratios are 2.45-1.45-1.00
So now, we don't have a clutch anymore, just a 2000rpm Convertor, I mean lets keep it fair.
Inside the TC is a hydraulic Torque Multiplier that has an infinitely and automatically variable ratio of between perhaps 1.8 and 1.1. The ratio is highest at Zero mph, and the ratio diminishes with less loading and with rpm/speed. So then at zero mph, to the pavement Your slanty might put
130 x1.8 x2.45 x3.23x24/24=1850 ftlbs. Compare that to 1120 above; this is 65% more torque to the road. So in other words, for the same level of take-off performance the automatic can use a lot less throttle, or less reargear.
But wait, that is at zero mph. Remember I said that the TC ratio diminishes as the car starts moving? What might it look like at 20mph about 2800 rpm. My math says about 160ft lbs at 2800, and the TC might be down to 1.4(WOT), so then
160 x1.4 x2.45 x3.23 =1770, compared to 1375 with the regular 4-speed; the A904 is still making 28% more to the road..
What if you installed just the 2800TC and say your current gear is 2.76s; I mean I don't know what you have just guessing worst case for this exercise.
So now when you floor it at zero-mph the engine spools up to 2800 instead of 2000, and the math looks like
160 x1.8 x2.45 x2.76= 1947 diminishing to say 1515 as the TC upshifts.
Compare that to 1120 increasing to 1375@ 2800 with std A833/3.23. So now,with 2.76s you start out 74% stronger at zero-mph where it counts, and still end up 10% ahead at he top! Good deal
But that's not the end of it; the A833/3.23 will cruise at 65=2956, versus ; with the A904/2.76s
65=2525 @zero-slip, perhaps 100 to 150 more depending on terrain, but likely never more than 2725. If you add a loc-up to that, then 2525.; another good deal * still using 24" tall tires.
So as the math shows, for first gear only and for same throttle settings. the 2800TC and 2.76s will out perform the A833 with 3.23s. That is the crazy ingenuity of the Convertor.
I agree 100% with RRR as to not using the od box , for two reasons at least.
1) the rpm drop from first going into second is huge. going from 3000 to 1620. If you are in a hurry, then you will have to rev it out pretty high in first only to be stopped at 1620 rpm and no more pull.
2)trying to put the engine at a sweetspot to cruise 3200 in second gear requires about 3.73s for 32=2800rpm Which is not bad, except your starter gear is now 11.53, and when in a hurry, you will want to rev that to 3700/23mph to get into second at a meager 2000rpm. So really, 23 mph is a bad speed to be driving at, seeing as how your choices are 3700 and 2000.
Same scenario for a regular A833/3.73s is
3200=32mph, and the starter is 9.92 so 3200 in first is 23 mph, and on the shift the Rs drop to 2340
So if you look at that you see that 23mph is 3700 with the od and only 3200 in the standard box, while on the 1-2 shift, the Rs drop to 2000 with the od box versus 2340 with the A833. And 32 mph is 2800 with the od box versus 3230 with the A833. So in every case the standard box offers better acceleration capabilities , except right on the take-off.
But yeah, you could run 3200/2800=14.3% more rear gear to even up second gears, but that puts your rear gear at 4.30s, and your starter at a ridiculous 13.29, and your final drive to be 3.14 in overdrive. Lemme show you how that stacks up;
9.92-7.16-5.22-3.73 with the A833/3.73s, and
13.29-7.18-4.30-3.14 with the od box and 4.30s
Notice that both third and fourth in the standard box are better than the same gears, in the od box.
Now lemme throw in the Commando box, Remember it is like the standard box but with the 3.09 low
11.53-7.16-5.22-3.73 Purrrrrrfect, for a city car. But because of the tight splits, I suppose you could run a lower-number rear gear, especially if yur not into fast take-offs.
Ok one more; lemme show you a 904 lock-up with 2.94s. The A904 ratios are
2.45-1.45-1.00 and with the 2.94s I get
7.20-4.26-2.94 but at WOT, it will act something like this,
12.96 diminishing to 10.08-5.11-3.23-2.94 Count them. I get
12.96-9.36-5.96-3.23-2.94 = 5 gears. with splits of .79-.64-.54-.91 and 65=2690 with 24s
The first two are in the TC so you never know that they are there but the engine sure does. And the last is the loc-up also an automatic feature. With the stock convertor, this is only worth about 200 or 300 rpm at WOT. But if you had a 2800 or more TC it would be worth more.
For more fun put a semi-auto shift kit into it. These shift normally in auto mode, but you can yank the shifter into any gear at any time and can hold it in chosen gear until you float the valves.
Ok so if you have read this far
Happy HotRodding.
. It does have Vintage Air, a rebuilt front end, Helwig sway bars, performance leafs and torsion bars, Coker Firestones, a mini-amp with aux input under the seat, new seat covers and carpet, and a ~7/10 body.
