901/20 and 901/21 motors

[chris_seven]

I relalise the subject of 911Rs may be a bit boring but I am trying to fix the spec of a new car that is just starting build and I am tring to get it right.

The 911R is commonly described as having either 901/20 or 901/21 motors.

I understand that the 901/20 has 46IDA Webers and Twin Plugs and a Marelli S121 Type Dizzy. This engine is quoted at 210 BHP DIN

I believe that the 901/21 was very similar but had slide throttles and MFI. I think this motor was rated at 230BHP DIN.

I think there were about 9 cars fitted with the 901/21 and the rest had the 901/20.

The 901/20 was also shown as being fitted to the 904GTS and the 906 and it is the basic variant we are trying to replicate.

I am concerned about the ignition system.

I have always belived that the 911R had a 'semi-transistorised' ignition but this would not have been fitted to the 904GTS or the 906 (?)

I have an early Marelli S121 Dizzy with 4 x Contact Breakers and a 3 lobe rotor and it is fitted with a pair of condensors.

A transistorised ignition would not need the condensors.

I would like to fit the car with 2 x Bosch Blue Coils and a basic Kettering Igntiton unless I am wrong in my assumption.

Does anyone know?



The dizzy is just being overhauled but the top sections is in quite good order.

Thanks

Chris

[gled49]

No condensers with CDI. Any conventional points condenser system will burn the points. Wouldn't consider using that distributor with out CD. I always convert to single Pertronix to drive twin CD boxes. Jerry Woods has always done this conversion for us. Gordon

[chris_seven]

My concern is that I don't want to use an electronic ignition if this wasn't fitted to the 901/20 type motors.

If 901/20s did use electonic ignition I will remove the condensors but I am not too keen to modify the Marelli unit in any other way as I guess it may be quite rare.