[Signkutter]

Originally Posted by jocko

I'm assuming your C20 already has a 4.10 in it, yes? 4.10 is a good gear for a C20. What was your original trans? Note that a 700R4 doesn't just give you lower highway rpms, it has a deeper first gear than most 3-speed automatics as well - so, in 1st gear, a 4.10/700R4 is approximately the same as a 4.98/TH350... If you've ever driven a 4.88 or 5.14 with an older trans, well, you get the idea. So, if you plan to do any hauling or camper-ing, etc, (or hauling 1000 lbs regularly) I'd want that 700R4 a little beefed up personally. Especially if you plan to ever floor it from a dead stop (ala the 4.98 comparison.. can and will damage the weak link, whatever that happens to be - u joint, trans, etc)
Don't forget you'll need a means of locking up the torque converter in o/d and that line pressure setup is critical before running (recommend EZ-TV thing from Bowtie Overdrives. They are also a wealth of good info, even just on the website).

With that tire and 4.10s, here are your 1st gear torque multiplication and cruising rpm comparisons to a TH350 and TH400:

A very informative post Jocko , thanks. What are the problems that arise if the torque converter isn't locked in o/d?