Just in case......
 

The72-73 911 used a variety of cases for the 2.4 ltr motor..3R 4R ,5R,and 7R and we've all heard variations on a theme as to which case is most suitable for a specific rebuild (2.5 vs 2.7 vs 2.8) Why did Porsche use so many different cases those two years and why are the 3R and 7R more frequently discussed in the rebuild forums. What about the 4R and 5R...are these guys the "black sheep"? Jack, Wayne are you out there...come in, come in please!

I believe on the 72/73 non-CIS cars, that the cases were 4R on one side and 5R on the other. These were internal markings, and were just used to differentiate amongst the different levels and iterations of designs.

The 7R cases are the strongest of the mag cases...

-Wayne

How much(much?) horsepower can you reliably make with the 4R 5R case? I know the 73 RS made 210 but did it have a 4R or a 7R case? It would be nice to make my 73T into a 2.5 Short stroke or a 2.7 RS spec but I don't know if it could handle that much torque.