I have a 91 850i and a 85 635Csi, both of which use the 4HP22 trans. Is it possible to modify the stock converters for higher stall while retaining the lock-up? I'm looking for around 2500rpm stall speed on both. I understand that the 850(330hp) and the 635 (180hp) converters would need different set-ups for the same stall speed.
Or is there a smaller dia. converter from smaller displacement BMWs that would fit?