Is this a fake supercharger set up ?

Fast Eddie

Fast Eddie

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Can someone explain how this set up works?

Carbs work on a vacuum, relying on the Venturi principle to draw fuel through the jets.

If a carb if fed air under pressure, how does this work??

Is it simply a fake blower ??


 
Superchargers were around long before fuel injection. Many prewar racers (BMW, AJS, et al) were blown.
So it must work.
The venturi is a relative low pressure caused by the narrowing of the inlet tract through the carb.
I suppose it might depend on what pressure? the carb bowls see?
Cheers & thanks for posting.
 
robs ss said:
Superchargers were around long before fuel injection. Many prewar racers (BMW, AJS, et al) were blown.
So it must work.
The venturi is a relative low pressure caused by the narrowing of the inlet tract through the carb.
I suppose it might depend on what pressure? the carb bowls see?
Cheers & thanks for posting.
Click to expand...
Of course.

But my understanding is that the carb is normally mounted upstream of the blower, so the blower is sucking air through the carb…
 
hybridracer said:
The carb float bowl connection to the atmosphere is connected to the pressurised air from the supercharger.
Click to expand...
Also known as a "blow through" supercharger setup.

Paxton did it on automotive setups 70 years ago. (Others as well)

Here is a modern retro design
www.summitracing.com

Paxton Automotive Corp. 1001864SL Paxton NOVI-1200SL Entry-Level Supercharger Kits | Summit Racing

Free Shipping - Paxton NOVI-1200SL Entry-Level Supercharger Kits with qualifying orders of $109. Shop Superchargers, Centrifugal Style Kits at Summit Racing.
www.summitracing.com www.summitracing.com

As mentioned, because the float bowl is pressurised as well, the venturi still creates the needed "vacuum" which is really a "pressure differential"
 
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concours said:
Also known as a "blow through" supercharger setup.

Paxton did it on automotive setups 70 years ago. (Others as well)

Here is a modern retro design
www.summitracing.com

Paxton Automotive Corp. 1001864SL Paxton NOVI-1200SL Entry-Level Supercharger Kits | Summit Racing

Free Shipping - Paxton NOVI-1200SL Entry-Level Supercharger Kits with qualifying orders of $109. Shop Superchargers, Centrifugal Style Kits at Summit Racing.
www.summitracing.com www.summitracing.com

As mentioned, because the float bowl is pressurised as well, the venturi still creates the needed "vacuum" which is really a "pressure differential"
Click to expand...
Never heard of a blow through system before. But YouTube has! Very interesting.

Seems to have merit especially when related to turbos on buying inch car engines. I’m still struggling with the reasons for doing this with Amal carbs and the practicalities of exactly how he did it.

Interesting stuff though.

 
Fast Eddie said:
Never heard of a blow through system before. But YouTube has! Very interesting.

Seems to have merit especially when related to turbos on buying inch car engines. I’m still struggling with the reasons for doing this with Amal carbs and the practicalities of exactly how he did it.

Interesting stuff though.

Click to expand...

That "art" bike shown makes no engineering sense at many levels.
🚽🤮
 
hybridracer said:
The Norton rotary race bikes used ram air to give a mild supercharging effect at high speeds and the Amal mk2 concentric carbs had their vents connected to the intake plenum chamber.
Click to expand...
MK1s don’t have those vents, so he must have plumbed in some alternative, tickler entrances perhaps ?

But thinking further on this, he must have used a fuel pump as well, otherwise the float bowls wouldn’t allow gravity fed fuel to enter the pressurised float bowls ?
 
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A venturi doesn't care whether it is being created by pressure on one side, or vacuum on the other. All it cares about is airflow at a point of restriction, with differential pressure causing suction in/at an orifice at the point of restriction. Either impetus will cause suction.

(unless I'm mistaken, which I am always at risk of being)
 
Suck through is an easier engineering problem since the carb doesn't know whether it's a piston going down a cylinder producing the negative pressure or the supercharger pulling on it, and the float bowl pressure is identical to the outside of the carb mouth (atmospheric.) Blow through changes the dynamics of the carb significantly and jetting would be much different from normal.
 
hhh said:
Suck through is an easier engineering problem since the carb doesn't know whether it's a piston going down a cylinder producing the negative pressure or the supercharger pulling on it, and the float bowl pressure is identical to the outside of the carb mouth (atmospheric.) Blow through changes the dynamics of the carb significantly and jetting would be much different from normal.
Click to expand...
Ah, so...

That makes sense.
 
I have never had a modern bike with an air box, but apparently the whole thing is designed to resonate, and create a supercharging effect. It is usually fed from the front of the fairing and encloses the fuel system. There is probably provision for pressure compensation for the fuel tank. Many years ago, some guys used to run a large diameter tube from the front of a race bike to the carburetor to supply cool air. It might have done something. I was interested in a couple of comments about Joe Craig. Apparently he used to run the Nortons very lean, and had been talking to combustion engineers.
 
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my suck through setup

Is this a fake supercharger set up ?
 
Fast Eddie said:
Fabulous !
Click to expand...
thanks I choose the FCR carb because it has push/pull cables and rollers on the slide, to make sure the slide does not stick. The supercharger creates alot of vacuum. Also it has an accelerator pump , that makes starting cold very easy, about five throttle turns/squirts and its good to go as the intake length is pretty long including the supercharger. And the pump also gives the bike considerable urge before boost. However that carb is big, and tall, making the fit a pain
 
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