I have been eagerly waiting for someone who owns a Volumetrico or 037 Stradle to answer this post, but it has not happened so I will l chime in.
I do not have a Fiat 131 Volumetrico or Lancia 037, but I do own a couple Volumex conversions that I have built. As far as the Volumex supercharger go here are some facts. The Volumex supercharger on the Fiat 124 spider it has 1 less tooth on the supercharger drive pulley compared with the Volumex supercharger on a Lancia Beta VX. The smaller diameter pulley spins the supercharger faster resulting in a little more boost. The Lancia Beta Volumex came from the factory developing 6-7 PSI of boost, so the Fiat spider Volumex should develop slightly more boost. The supercharger that came on the Fiat 131Volumerico is much larger than the Volumex supercharger but it spins much slower due to the larger diameter pulley on the supercharger. The Volumetrico supercharger, the Lancia 037 Stradle supercharger and the Lancia Rally EVO I supercharger all have the same displacement. The Lancia 037 Stradle came from Abarth delivering only 7 PSI of boost, yet developed 205 HP. From pictures I have seen of Stradle engines, the supercharger pulley and the crank pulley are similar in diameter so the drive ratio must be around 1 to 1. Guy has possibly worked on one of these engines so he could tell you for sure. Guy may also be able to tell you the drive ratio on the rally car engines. The rally cars developed more boost by spinning the superchargers faster and then later (EVOII) by an even larger 3 port supercharger. Take a look at the information below, some of which I got from Voltas web site, Lanciarally037.com.
Lancia 037 rally car, not the Lancia 037 Stradle
EVO I ENGINE:
Centre-rear longitudinally mounted, four cylinders in line, bore 84 mm, stroke 90 mm, 1995 cc, compression ratio 7,5:1. Max. torque at 30.5 mKg at 5000 rpm. Max. power from 255 to 280 bhp at 8000 rpm. 255 hp on carb, 280 hp on mechanical fuel injection.
EVO II ENGINE:
Centre-rear longitudinally mounted, four cylinders in line, bore 85 mm, stroke 93 mm, 2111 cc, compression ratio 9:1. Max. torque at 34 mKg at 5500 rpm. Max. power from 310 to 325 bhp at 8000 rpm.
Roots Volumex compressor type ABARTH with variable pressure from 0.60 to 0.90 bar, increased and powered to 1 bar for EVO II version
On your oiling question. The Volumetrico and 037 superchargers have their own oil pump at the rear of the supercharger. I do not know for sure if it is used for evacuation or pressurization. Hopefully a Fiat 131 Volumetrico owner and or Lancia 037 owner can help fill in the blanks.
GC book 6