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Two Feathers

52 Posts

Posted - 23 Dec 2017 :  12:54:42 PM  Show Profile  Reply with Quote
Time to do something with my auto. Tranny/ torque converter and rear end. I'm looking for advice. Want to change out the rear end to a posi with 373 gears. Engine is from a 68 GTO, 400ci with XE274H cam (230/236 duration). Current Tranny is a T350 I believe, leaking badly, metal fragments, grinding, time to go.
Weekend driver but not at the track. But, I do like power when I want to use it.
Also looking for advice on a shop, I live in Maryland. Mr. Pbody is an option if he does this type of work. Let me know.
Thanks for the advice!

Edited by - cconserva on 23 Dec 2017 1:03:46 PM

Blued and Painted

3432 Posts

Posted - 24 Dec 2017 :  10:50:24 AM  Show Profile  Reply with Quote
Th350 is a tough and reliable transmission. If put together correctly, it should handle over 400 HP.
The 3.73 gear is great in a 4 speed car where stop light to stop light performance is desired. For reasonable RPM's at highway speeds (70mph), an over drive automatic would work with this gear.
This grumpy old guy would not go more than a 3.42 gear with a 3 speed automatic. But that's just me.

Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Sitting Bull

126 Posts

Posted - 24 Dec 2017 :  12:44:17 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
My cousin ran high-12's with a nice THM 350, about 3500 stall, and 3.23 gears. My '67 Firebird ran 11.2's with 3.42 gears, a THM 350, and a custom Hughes converter that flashed to around 3600rpm.

Unless you are running some REALLY tall tires, or an overdrive transmission, the 3.73 gears will be miserable on the highway.

Now, if you want overdrive, I urge you to go modern. Have a 4L60 built, use a lockup converter, and there are several companies that make TCU (transmission control computer) which will allow you to fine-tune the transmission to shift exactly like you want it to.

CURRENT: '73 T/A clone, boring at the moment...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
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