I know of 2 Supras in the Houston area with 3800rpm+ stall speeds but the trannys are built up. I've not heard of anyone running that high of a stall with the stock tranny.
You should contact Nicky Coleman at Coleman/Taylor Transmissions in TN (901)237-2520 He has raced several MKIV TT auto cars in the past and is very helpful.
I ran a 3800 stall TC on my factory tranny and single turbo setup for quite a while and the tranny never showed any signs of damage. I ulitmately went with a built tranny because I wanted to make more power and wanted an upgraded valve body for firmer shifts, but not simply because of the higher stall TC.
MAKE SURE YOU GET A GOOD TRANNY COOLER as soon as you install the new TC. DO NOT WAIT for several weeks or months before installing it. The higher stall TC creates much more heat than the stock unit and that's what kills transmissions. Make sure you get as big a tranny cooler as you can fit up front. I think Summit sells one with a built in fan for like $150. It's the best investment you'll ever make.
Yea I wanted to know the same thing... If I get an SP57 I wont be able to afford the SP or any tranny right away... I was gonna get a 3200 or maybe 3800rpm staul TC... I figure the SP57 is right on the border of the power limit the tranny can hold anyway.. I would think the better TC could help handle some of that extra power?... Ill definately get a tranny cooler.
Yes you can run a 4200 stall on a stock tranny. You will want a large tranny cooler to help deal with the extra heat though. Frequent tranny fluid flushes won't hurt either. I flush my tranny fluid on the order of every 6,000 miles. Eventually you will need a built tranny though.