Pre war supercharged Comet..........Zoller supercharger.

[Chris Launders]

I think the long induction pipe from the supercharger is actually a benefit as it acts as a reservoir damping out some of the pulses associated with running a supercharger on a single cylinder. The Velocette "Whiffling Clara" actually had a large plenum chamber for this reason.

 

[greg brillus]

Yes ......Small capacity engines that are supercharged tend to suffer from the pulsing affect that the rotor of the blower delivers .......More so on roots types that have 2 or 3 lobes per rotor, the vein types not as high I would have thought........Thus the need for a makeshift "Plenum" is the norm to give the pressure side some volume to lessen the affect........I can't remember exactly but the change from throttle open to fully closed can be an issue with a supercharged engine as well........Common to have a safety pressure relief valve in the manifold somewhere as well........a backfire could be disastrous........On big radial aircraft engines, the many short elbow like inlet manifolds will split right open on a descent backfire on start up. I have seen a few supercharged post war twins, speedway bikes and sprinters.......these definitely have a longer tube/plenum type of inlet system on the pressure side of the blower. And they always have a "Blow off" valve in this plenum arrangement. One issue on closing the throttle is the tendency for the intake to "Pool up with fuel" then once the throttle is opened, the mixture is very rich.........I'm sure that is one of the main reasons as well for the longer intake.

 

[Comet Rider]

Hi Greg,
On modern dragbikes and cars it's now more common to have a burst disc or panel.
On my old funnybike I had 2 burst discs, one at each end of the plenum chamber. The discs were made from Pepsi cola cans, which were the perfect thickness and would burst around 70 PSI

 

[highbury731]

Whiffling Clara was also abandoned and returned to atmospheric induction. The pulsating inlet on a single is just too irregular. The more cylinders, the less this effect. I think it is significant that the only successful single cylinder supercharged bikes are Mighty Mouse and Super Mouse* - the issues of varying throttle disappear on a sprint bike.
In the 1980s, Honda turbocharged the CX650, and that had lots of problems due to the irregular and infrequent intake pulses.
* Super Mouse is a twin, but each cylinder has its own supercharger, so it functions as two singles.
Paul

 

[Cyborg]

Whiffling Clara was also abandoned and returned to atmospheric induction. The pulsating inlet on a single is just too irregular. The more cylinders, the less this effect. I think it is significant that the only successful single cylinder supercharged bikes are Mighty Mouse and Super Mouse* - the issues of varying throttle disappear on a sprint bike.
In the 1980s, Honda turbocharged the CX650, and that had lots of problems due to the irregular and infrequent intake pulses.
* Super Mouse is a twin, but each cylinder has its own supercharger, so it functions as two singles.
Paul

What sort of problems did it cause on the CX?

 

[Bill Thomas]

I read one problem was the turbo ran on after switching off, With no oil supply !,
So if you blipped the throttle before switching off , You were in trouble ?.

 

[Cyborg]

I read one problem was the turbo ran on after switching off, With no oil supply !,
So if you blipped the throttle before switching off , You were in trouble ?.

Don’t want to highjack Greg’s thread, but blipping the throttle before shut down has never been a good idea. Hopefully it has come down from the 180,000 rpm or whatever it spun at. There was an oil restrictor in the turbo feed line that would maintain some residual pressure to feed the bearings after shut down. Turbocharging a twin was challenging, but in my experience, they did well to overcome any issues. They were exploring new ground at the time and took a slightly different approach. What they learned from the 500 was incorporated into the 650. It was never intended to be a high production unit... literally more of a test bed..... anyway enough of that.

Here’s a link for you Greg. Hopefully it works and has some info you are interested in.

Triple-M Register

www.triple-mregister.org

 

[Simon Dinsdale]

I found a complete bike photo of one of the supercharged bikes in the collection of photos I have here so scanned it.
All it says on the back of the photo is 1936.

Simon

 

[highbury731]

What sort of problems did it cause on the CX?

The electronic computer management on the CX500T was a pioneering effort, in production four years before the supposedly first such system by Motorola for the Cosworth GBA V6 for use in F1.... Turbos don't like being rapidly accelerated and slowed down by the irregular exhaust and induction pulses. The computer techery made it work much better than it should have, but it had LOTS of turbo lag.

 

[A Nut]

Hi Greg,
Sorry that I have not replied sooner. I am still looking for the other photos. The only one in my file is the one from the back quarter showing the HRD logo cast into the back of the blower. I have long thought of trying to manufacture a blower for my bike and went as far as contacting Ivan Rhodes regarding his supercharged Velo. He told me that Velocette used a converted Spencer vacuum pump! He employed a specialist firm to make his. I understand that the drive was by a chain similar to the primary drive but with an outrigger bearing from the magneto drive. Do you think that it would be better to use a toothed belt drive and pulleys as it would absorb some of the shock loading? (Not original but probably much better) I would be interested in some castings if and when you decide to go ahead.