Love this thing
.
Looks to be about 1.85:1 drive ratio, which is pretty quick for a Roots. Probably won't detonate the blower (anecdotally they should be good for ~14000rpm, or 7600rpm at the crank on that drive ratio... 7600rpm at the crank is pushing it for a grey, short of the forged-crank specials). However, it's hard to judge how it will behave. It may run out of puff - in their original use the blowers were operating closer to 2000rpm. In this case, even though you are spinning the crap out of it you may still just get "normal" bosst of 10spi or so. On the other hand, if the internals are tight it may generate a crapload more boost than you are anticipating (in theory up to 50psi at that drive ratio on a relatively standard grey). I'd be pretty cautious on startup, watching the boost gauge really carefully at anything above idle. You may be able to drop the pulley ratio (and lower the blower stress) without losing much boost. The 2-71 has 136ci/rev, compared to a Type 65 Norman (typical grey motor blower) at 118ci/rev). This means you could run it a poofteenth slower than the Normans, which normally run close to 1:1 at 5-7psi.
I can't see a relief valve in the picture, though it could be hidden by the camera angle. Definitely needs one, especially if it is wizzing around at those speeds. Anyone doubting the need for a relief valve should watch this:
https://www.youtube.com/watch?v=Ll3EvNMBgLA.
The 2" SU should be fine - good choice.
I'd love to see how that crankshaft pulley was put together - looks like a gilmer pulley bolted onto the aftermarket harmonic balancer, with three extra holes drilled to give a total of six bolts.
The breathers on the rocker cover look cool.
Gary - if you're reading this, we may need to make up braces from the top of the cylinder head to the manifold, similar to these ones, at some stage.
Cheers,
Harv (deputy aprentice Norman supercahrger fiddler).
