Don't do it. Don't put 3.23s behind the od. First gear will be just fine. And it will cruise real nice with the equivalent to 2.78s. But third will suck, and second almost as much. This is really a wrong tranny for a 340. To keep a 340 on the pipe requires a close ratio tranny, and the od is a very wide ratio. Not just wide but very wide.
With 3.23s, first will be good to about 52 mph@6500. Then when you shift into 2nd the Rs will drop to 3485, and the poor 340 is nearly 1000 rpm under it's torque peak(depending on combo of course, but 600 for sure). So in a performance situation,she will be a bit of a slug til it hits say 4200 which will be 63 mph.So for 11 mph, from 52 to 63 the poor 340 will struggle. Then it hits the pipe and sings to 97 mph, through the traps. Two gears. That is not the fast way down the road.
But ok, never mind the track.
Say you just cruise the car. With 3.23s 4000rpm is about 32 in first,60 in second. So then what is third good for? Going 5 mph to hit O/D?
Ok try another one; You are cruising along in 2nd at 35mph doing about 2345 rpm. That's nice right? But say you want to speed up. A 340 has little torque at 2345. A teener could have more. You're gonna have to lean harder on the gas to get moving. But downshift!, you say. Ok, well 35 in first is 4340. Now the 340 has all kinds of torque, but it is screaming.
The o/d tranny is a tranny to fit a low-rpm engine, with plenty of torque, in a low to medium performance application. So if your 340 has a teener cam in it and there is nothing left in it after 4500rpm, then this would be a good tranny for it;maybe even with 3.23s; but 3.55s would be better, and 3.73s even better, and 3.91s best.
FWIW;
I ran this tranny behind a warmed up low-compression teener and 3.55s. It was pretty good. But as you can imagine, the teener was sloooow. So I put a GearVendor unit behind it and learned to split gears. That was pretty sweet. But now I had double overdrive, sooooo you guessed it; out came the 3.55s. And in went 4.30s. Well that teener turned into a terror. But I found 3.09 x 4.30 a bit much as a starter gear, so in went 3.91s. That was the magic number. A starter gear of 12.08, and a cruiser of 2.165. with 7 useable gears. 90mph was 2400ish rpm. Yeah it pulled it.....
So to recap;
3.23s,plus A833od, plus 340 equals bad idea.And
3.91s,plus A833od, plus 340,equals sorta doable. Or
3.91s to 3.73s,plus A833od,plus stock type teener,plus GearVendor splitter equals great idea!
