I'm getting a car with a TH350. My Vette had a TH400. I've been led to believe the 400 is a better. I'd want to shift it manually. Is that tough to convert on either? Is it worth it for autocross or the occasional drag? Want to be challenge friendly regardless.
Thanks!
The TH400 is much stronger but the drag racers use TH350s because they are lighter, have less parasitic loss, and are strong enough.
I regularly serviced a '67 Camaro that had a progression of 468, 496, and 540ci big block engines... still the same TH350 behind them all. Heck I had to rebuild the 12-bolt once, too.
Because it is kind of the de facto 3 speed drag trans, you can get manual valvebodys in forward pattern, reverse pattern, and with or without engine braking. You'll probably want one with engine braking, and my personal preference is reverse pattern (PRN123). You might be able to find a valve body cheap on eBay or some other place where used parts are sold. A ratchet shifter is highly recommended.
The C6 in my first car had a Pro-Matic 2 shifter and an I-forget-what manual valve body, and it was just a street car. The valve body I installed shifted HARSH, though, and I got very good at replacing U joints as a result. 4800lb car with a big block, C6, and 9", the U joints were the weak link in the system 
For the baller on a budget, I've always kinda wondered what would happen if you took the springs entirely off of the governor. In theory, that would make D position always 3rd gear since it would "think" you were going like 180mph. So it'd be like a forward pattern manual setup, without spending a couple hundred bucks on a valve body. Still would want a ratchet shifter, though, as it 100% prevents overshifting.
vwcorvette (Forum Supporter) said:I've been led to believe the 400 is a better.
Better? In what way?
The 400 is significantly larger, heavier and turns more of your precious horsepower into transmission fluid heat. It was designed for big blocks in trucks so it can handle higher torque stock for stock but the 350 has all the aftermarket support to take it to the same levels.
Iirc the 400 would require a different crossmember and a shorter driveshaft
Pete. (l33t FS) said:For the baller on a budget, I've always kinda wondered what would happen if you took the springs entirely off of the governor. In theory, that would make D position always 3rd gear since it would "think" you were going like 180mph. So it'd be like a forward pattern manual setup, without spending a couple hundred bucks on a valve body. Still would want a ratchet shifter, though, as it 100% prevents overshifting.
I drove a Mercedes 722.3 in a Porsche 928 that I was led to believe had this exact mod because no aftermarket full manual exists for that trans. Full line pressure and full manual shifting. We were driving it in 2-3 most of the time and it was fantastic.
Trent said:vwcorvette (Forum Supporter) said:I've been led to believe the 400 is a better.
Better? In what way?
it can handle higher torque stock for stock
I think in that way.
I think it's been said. TH400 is heavy and strong. My '85 C30 Dooley has one in it. According to the author of this article, it's "the toughest domestic automatic ever done."
People rag on these because by today's standards, they're inefficient, but one thing they didn't do is leave you with expensive repair bills before you had 100k on the odometer like some of the silly seven, eight, and nine-speed junk they put in cars today. The TH transmissions were capable of outlasting every other part of your vehicle, and there's something to be said for that.
https://www.motortrend.com/how-to/1805-upgrading-the-turbo-400-in-your-corvette/
Build the TH350 to fit your use case. There are so many options to build it to as strong as you need it to be within reason. As an added bonus, You don't need to change a thing to mount it. At what ever age it is. (Probably 35+ years old) it'll need a rebuild anyways for any performance application.
TH350 doesn't take much money to make it as strong or stronger than a TH400.
TH400 shares reverse with first, so not only do you have heavy things spinning inside, the 1-2 shift has to overcome a reverse-spinning drum and get it moving forward again. Fantastic trans for heavy duty stuff, but no need for drag/cross/challenge race.
I would do a full-manual valve body, Sonnax "corvette" 1-2 servo, and set up the valve body for medium-firm shifts. Medium firm is more than enough to keep clutches happy, but full throttle on the hardest shifts can be a nightmare on u-joints and pinion bearings.
Not all valve bodies are the same. You have (or at least used to) have options to modify a stock valve body for full manual, but the factory passages will limit shift firmness and speed. I suggest a good aftermarket valve body if you can fit $300 into the budget. If not, you can get a factory valve body converted to full manual for about $150.
TCI and Hughes, yes. B&M, no. I don't think Sonnax makes one anymore, but they are a definite yes if you find one.
I'm out of the loop, but one of my plans was to do a ratcheting shifter for a TH350 to make poor man's flappy paddles by just bumping a shifter. As of 10 years ago, no one made a good ratchet shifter. They were all complex beasts that required intense adjustment for setup and continual adjustment every season. If they're not perfect, you can get a shifter stuck between detents and fry clutches fast. You can use a stock shifter with a full manual VB, but it's not quite as reliable as whacking a shifter. Easy to have your hands off the wheel for a bit longer, and easier to move two detents instead of one. In a drag race, probably fine. Autocross, I would want a proper ratchet.
I'm sure someone makes servo-operated flappy paddles to control the shift cable, but likely super-spendy.
Edit to add: Make sure you know if your TH350 is a "C" or not (lockup converter). You'll have to buy the appropriate valve body for the right trans or they won't work. There are also some mild differences between variants. Olds and Buick had a different valve body for a few years for silky shifts, yadda yadds. When you take your old one off, there should be a one or two digit code on the separator plate that can help narrow it down.
Second edit to add: If your manual kit doesn't come with a new separator plate, get one. They're like $20. Over time, the check balls hammer against the orifices in the plate and eventually press-fit themselves in the hole, or fly through. Cheap insurance.
Dammit, third edit to add: If you don't have a TH350C with lockup, you might want to consider it. It won't make a huge difference other than heat, but you can modify things to lock up the converter once you reach second gear. Whether or not it helps speed/time is going to be based on the torque peak and your gearing/stall speed, but it's nice to have the option. Again, not a big deal at all, just something to consider.
bmw88rider said:Build the TH350 to fit your use case. There are so many options to build it to as strong as you need it to be within reason. As an added bonus, You don't need to change a thing to mount it. At what ever age it is. (Probably 35+ years old) it'll need a rebuild anyways for any performance application.
Considering what y'all are saying this seems the way to go. Unless I can get a super silly inexpensive manual. I'll be picking up the car and assorted parts this weekend and will start a build thread once I've gone thru everything.
Curtis, anymore edits before I move forward? LOL
I intend to use this for autocross and track events once past the Challenge if that helps. The only drag racing will likely be at the Challenge.
Edit: Probably.
Curtis73 (Forum Supporter) said: ....balls hammer against the orifices....
Apparently infinitenexus is not the only author on this board that writes erotica. 
In reply to Curtis73 (Forum Supporter) :
That 1-2 shift is what I had been trying to remember.
You'll need to log in to post.
