Porsche Factory twin-plug racing distributors, not usual to see them grouped in photos like these. I wanted to show a 'side-by-side' comparison between these twin-plug distributors used by Porsche in their competition engines.

Some of you have asked why the early Marelli distributors (see this photo https://pbase.com/image/53524544) will not fit the 'late' Magnesium and Aluminum crankcases and the answer is simple. The shaft diameter, as well as the method of locking the distributor in place, is very different. For example; the shaft diameter (O.D.) of the 'early' Marelli https://pbase.com/image/53524561 is 27mm while the 'late' Marelli https://pbase.com/image/53524563 and the subsequently released BOSCH Twin-Plug distributor of the 911 RSR https://pbase.com/image/53524564 and the BOSCH 935 https://pbase.com/image/53524565 both have a larger 30mm diameter (O.D.) shaft.

You may want to also visit the photo gallery of my 'early 2.0 liter Aluminum Crankcase Conversion' to the '911 RSR' crankcase 'spec' which includes the distributor modification to allow the use of the 'late' Marelli in an 'early' Aluminum crankcase. Take a look here https://pbase.com/slidevalve911rsr/myrsr_28ltr_aluminum_crankscase