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cconserva Posted - 23 Dec 2017 : 12:54:42 PM
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!
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Phil Posted - 19 Mar 2018 : 1:11:15 PM
I know this is from a few months ago and didn't see it until now. I run 200-4R's behind my Pontiacs and have since 1987. They are an excellent choice for your 400. It's basically a bolt in, including the existing driveshaft. Just slide the tranny crossmember back a little and in most A-Bodys there are already factory holes in the frame which line right up. If not, just drill them. These transmissions have a nice gear spread for the Pontiac, and a WOT shift to 4th (OD). There are no 'E' versions of the 200-4R as they are all operated by a simple Throttle Valve cable.

The 700-R4 (4L60/4L60E) is longer and a bit boxier/bulkier in the pan area, has a 3.06 1st/1.62 2nd and no WOT shift to OD but can be built satisfactorily. I avoid the E ones unless you want to spend quite a bit more with some additional items to install.

Contrary to urban legend, the TV cable set up IS stupidly simple unless you have a 1st grade math education. Difficulty is often dramatized by internet parrots who have never actually done it.
Lee Posted - 24 Dec 2017 : 12:44:17 PM
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.
Blued and Painted Posted - 24 Dec 2017 : 10:50:24 AM
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.

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