200R4 into 71 skylark 350

[Former Cav]

I have a 71 skylark custom with the 350-4v 260HP motor.
If I keep this motor UNDER 400 HP, how "much" of a 200R4 tranny will I need.
I've seen them priced from $1800 to $3800. I don't want to break the bank.
Also, I have 2.75 gears, I realize with the 200 R4 that low gear will be about 3.08 to one vs 2.45 to one in the existing TH350.
OD is what? .77 or so to 1 ?

 

[bob k. mando]

Overdrive on a 200r4 is .674 which makes for a 1.8535 after going through your 2.75 gear set.

200r4 HD is what GM put behind the turbo 6 motors from the 1980s, the GNs and black Regals and whatnot, so it should definitely be able to handle what you're doing unless you are going drag racing every week.

1st gear in a TH-350 is 2.520 x 2.750 == 6.93

however, i show that the A-body had a 2.73 option in 1971. the diff should be stamped with either 'LK' ( peg leg ) or 'LT' ( posi ).

so, using my numbers

trans  TH350 * 2.73     200r4 * 2.73
1st    2.520   6.880    2.741   7.483
2nd    1.520   4.150    1.568   4.281
3rd    1.000   2.730    1.000   2.730
4th                      .674   1.840

usage is probably more relevant to how much you want to spend on the trans than anything else. if you just want to chirp the tires once in a while, a Grand National spec trans will probably be fine. if you're drag racing every weekend you need to buy the best trans you can afford ... because you're going to break it eventually. and building it right the first time will last a LOT longer than saving a couple of shekels up front.