I am resurrecting this old thread because i had some ideas lately.
So far, in this forum, i have seen people substituting the Rover 4 cyl mainly with equivalent modern units for various reasons: Power (Turbocharged Rover T series, SAAB 2.3), everyday use (Ford 2 litre), economy (PSA diesel). My thoughts though are far from such motives. It's a well used "what if". Indeed, what if BL in the early seventies, instead of developing the 2200 4 pot engine, used the BMC inline E6 in 2200 or better still 2600 forms?
The idea is dismissed by Chris York some posts before, but i have second thoughts on this. Yes, the E series might not have been an exceptional unit, but the E6 was exceptionally smooth, and more or less within the same weight and dimentions with the terribly long and heavy Rover 4 cyl. The E6 2600 notably was used in the South African SD1s instead of the more common Triumph derived six, and people that have experienced both, state that the performance of the cars with the different engines was rather comparable. One can only take this as a compliment for the old BMC desigh.
On the other hand, the perception of the 4 cyl P6s by the early seventies has changed. It wasn't any more the sporty advanced 4 seater that used to be at it's launch. It was rather a quality car for those that they weren't really in a hurry. In this prospect, a smooth straight six with comparable if not better performance compared with the 4 cyl units would suit the car much better. I hasten to add here that my current TC doesn't have to worry. I believe that i should preserve as much as possible the original character of this car. But if i had a second P6 i would really like to try to create that "what might have been" along these lines.