Tuesday, August 7, 2012 :: View topic - "RARE" supercharger :: View topic - "RARE" supercharger
Bvilletom wrote:
I noticed this thread on the VW site (The Samba) and then again in by Keith LeBlanc. I raced a blown Honda S-90 in the seventies for 2 years with the same smog pump (blower) at Bonneville. I worked for Porsche & VW then & these little blowers came to the U.S. on ’68 or ’69 912 Porsches as a smog pump. I wondered then why a U.S. made pump came from Germany on a new Porsche 912 but looking back it was probably a stop-gap measure to make the car meet tightening smog laws. They were driven at about 2:1 with a vee belt on the 912’s and they didn’t live too long (20-30k miles) spinning up to about 12k rpm. What happened was the bearings in the gears ran out of oil and it seized up and broke the belt. It is just a small roots blower with straight steel lobes and sealed bearings at one end. We threw a lot of them away and most owners didn’t put them back on in the Midwest. They didn’t appear to be something you could rebuild. You should be able to find one at some small old Porsche shops.

On the S-90 I drove it with a small chain on the generator side at about 1:1, and that was too much boost. It would make 20psi very quickly. Trying to supercharge a single-cylinder small motor is very difficult. It becomes a rhythmic, surging, pulsing, tuning nightmare. I tried blow-through, draw-through, long manifolds, very long manifolds, short ones, and all kinds of plenums. The surge was very violent. It accelerated like a 350cc, really pulling hard, and the next second it would shut off – about throwing you over the handlebars. It felt like the carb quit flowing air momentarily. We finally got it reasonable by making a plenum out of ½ of a propane torch cylinder with Homelite pyramid reed valves on each end to keep the charge going in the right direction. There was another guy from (I think) Riverside CA. doing the same thing and I think his name was Fletcher Izzard, also with an S-90.

I had no problems at all with the blower. I would say it’s not going to pressurize much more than a 200cc 4 stroke motor because it can’t flow enough volume of air. I ported mine a little bit.

The man that rode my bike was Mike McCann (Lisbon IA) who is the man with the large white sun block on his nose pushing Burt Munroe off the line in the out-takes of The World’s Fastest Indian movie. I then was the young guy hanging out at the old Chevy garage in Wendover during Speed Week listening to all these old guys, Burt, Mike, Rollie Free, and others drinking beer and bench racing - telling tall stories. It doesn’t get any better than that!


Tom Bruch