9 replies to this topic

[DeadSquare]

I am eyeing up fitting and using half a 45 Webber in front of a "Bini supercharger on a round-nosed Mini.

 

It would squees in without the ram-pipes, but friends at the Motor Club insist that without the resonance of the trumpets, the Webber will perform no better than an un-rammed SU.

 

With the constant suck of the supercharger, there won't be the interrupted suck every other revolution that sets up the advantageous resonance.

 

The question is:-  How much difference is there in the delivery of the ideal fuel/air mixture between a Webber or an SU ?   In this case, a 45 and an 1.3/4"

 

 

[nicklouse]

Most of the supercharger Weber kits use both barrels.  
 

yes a ram pipe or stub stack will make a difference. With improvements of say 3-5% air flow.

 

now the HIF44 already has a radius on the mouth but still a stub stack gives impovements on the flow bench.

[Turbo Phil]

It’ll definitely hamper airflow with no radius at all. Can you not fit some short bellmouths?
From the testing I’ve done on an SU even a basic radius provided an increase.

Phil.

[nicklouse]

I seem to remember Vizzard commenting on the sharp corners effectively making the bore size smaller. So reducing the carb size.

[DeadSquare]

Most of the supercharger Weber kits use both barrels.  
 

yes a ram pipe or stub stack will make a difference. With improvements of say 3-5% air flow.

 

now the HIF44 already has a radius on the mouth but still a stub stack gives improvements on the flow bench.

 

The inlet of the Bini supercharger is a diabolical shape, so the adapter takes up room, and both barrels would make it longer.  Also, I know from the youthful exuberance of fitting a beautiful 2" SU  to my Shorrock on a frog-eyed Sprite, that the higher gas speed through an 1.1/2", gave better vaporisation and more torque.

 

As it is simple in a lathe, I always put a radius on an SU, if the filter permits.

 

[DeadSquare]

It’ll definitely hamper airflow with no radius at all. Can you not fit some short bellmouths?
From the testing I’ve done on an SU even a basic radius provided an increase.

Phil.

 

I have just under 3/4 inch between the inner wing and the Webber, too little really for the shortest bellmouth, so I intend to radius the carb inlet.

 

What the club boys are on about is that a Webber responds to the trumpet's resonance, so what I'm wondering, is it just the resonance of the trumpets that give a Webber the edge over a trumpet-less SU ?

 

Assuming that both carb's inlets are radiused to ease air flow, without a trumpet and no resonance because the supercharger is constantly sucking, is the performance of a Webber on a par with an SU, or better;   or maybe worse as they are reasoning?

[DeadSquare]

I seem to remember Vizzard commenting on the sharp corners effectively making the bore size smaller. So reducing the carb size.

 

Before precision die-casting there was more "meat" in the body of an SU, and I remember Barry William's father, tapering the inlet side of a pair of SU until the flange had to be supported with Araldite.  The regs permitted the bore of the carb to be polished but didn't stipulate how little the polishing had to be.

[timmy850]

I’d rather use both barrels of a 40mm Weber with some smaller chokes than one side of a 45mm with a big choke

I’ve used a Dellorto DHLA for years with only a radius milled on entry to the choke and it’s run really nice

[OzOAP]

I use Thunder Productions weber 'stacks'
Look them up.

[DeadSquare]

I use Thunder Productions weber 'stacks'
Look them up.

Thank you for pointing me at that. Reminds me of the "Mega" on a JAP engined, 1950s, Formula 3

Maybe not quite as shiny as Thunder's, but with it as a pattern, I have crafted something quite pretty on the inlet of an SU, out of Isopon.