Advantages? Your first gear would be shorter, meaning you would get away from stop signs a bit faster. Personally, I think it is a lot of work with only marginal improvements. -Bob Cunningham
I agree as you are giving up the VP converter. Probably not much advantage unless you are looking at racing the car. Then a high-stall converter and TH350 might get you going a little faster. For mileage and efficiency I doubt there is much difference for a daily driver.
One advantage is parts availability. I had quite a time trying to find a replacement pump assembly for my ST-300 transmission. Along the way I found plenty of TH-350's available, cheap. In fact, it cost more for the pump ($85) than it would've for a TH-350 ($75). That being said, the performance advantage is that you'd gain a first gear. The ST-300 has two speeds, 1.65:1 (or so) and 1:1. A TH-350 adds a lower gear, around 2.5:1. In effect, the "L" of an ST-300 is the equivalent of 2nd gear in a TH-350. Also in my search I lamented to one tranny shop that if I couldn't find parts for my ST-300 I would throw in an TH-350. He said that if you were going through that trouble, put in a 700R4 instead and get overdrive. He specifically recommended the year '88 through '92 as being the best candidates - earlier years had some reliability issues and later years had computers.
trans most 700r4 trans are chevy bolt pattern most 2004r have both bolt patterns just in case you go overdrive. bowtieoverdrives.com would be a good place to check them out. did you find a good converter rebuild place? i think mine slips in high andy
