Basically, from my reasearch on the same topic, it seems that the deal is this:
For reasonably-powered engines, a built-up overdrive automatic is the better choice. Personally, I'm leaning toward the 200-4R over the 700-R4, since it has better ratios. I think the best description I've heard of the difference between the two is that the 200-4R is esssentially a close-ratio transmission, while the 700-R4 has a wider spread.
Close is better, IMO
For high-powered engines, the GM overdrive automatics just can't cut it. You start talking about a radical engine (say, 600-hp), and those transmissions start falling to pieces very quickly.
So, when dealing with an extremely powerful engine, you may have no choice but to run something like a TH400. So, if you want overdrive, you need something like the GearVendors unit. That allows you to run lower revs on the highway, or a more agressive rear gear, or some combination of the two.
I'm
currently curious about the possibility of mounting the gear splitter to the differential, instead of the transmission. I haven't pursued it, but at some point I plan on dropping GearVendors a line and seeing what they think. Personally, I think it would be a stronger system (less stress of the driveshaft), and have a better weight balance (I don't like adding weight to the front of the car - in my opinion, it should be something like 49/51 balanced, so it will go to 50/50 during braking when handling needs to be best).
Joe
