I am just looking for a "proper" petcock valve: that can fit into the (metric?) thread of the radiator that drains the coolant in a reasonable amount of time (current valve requires more than half an hour on a cold engine). that spills coolant more or less in the same direction during the process. the possibility to attach a hose would be a plus! My car is a 400i, but I presume they used the same valve on all the cars of that era.
The drain valve on vintage FIM radiators is M14x1. This is not a standard metric size. I machined a 19mm (3/4") solid brass hex-head plug to replace the drain valve. To drain the radiator, I remove the plug and coolant splashes all over the bottom of the engine, but the radiator drains very quickly. You just have to live with the fact that draining the coolant creates a big mess both on the car and the floor. FYI - you should warm-up the engine before draining the coolant so the thermostat opens; this allows the engine block to drain as well.
I am guessing you are correct about fit. The 103948 and 101488 are both for 308. I bet one of the 2 fit. There are 14 x 1.0 14 x 1.5 available and in stock at Maranello Classic.
The vintage drain plug is 252840 and was made by FIM. I assume it came with the radiator which was installed by Ferrari on the assembly line. The current part number is 101488, and it's available at Maranello Parts in the UK.
Thanks @wmuno for the alert on the thread pitch. I do have an original valve and really don't like it as it really takes ages to drain the radiator and makes an horrible mess, which is a problem for the friends that are kind enough to let me use their garage! I will probably buy a male M14x1.0 to female M14x1.5 adapter (https://www.fittings.space/gbm21-m14x15f-m14x10m) and use a regular petcock.
On the 250 series cars I have epoxied a 1 inch long brass tube inside the outlet in the wing nut and use a standard 1/8 inch hose to run to a container. While this takes a while to completely drain the coolant, there is no mess. This even works without a lift if a shallow pan is used.
