Lotus Elan and Lotus Elan Plus 2 Forums

rgh0 wrote:

A Stromberg head may flow better on a flow bench but as the ports are Siamesed it does not breath as well in real life on an engine due to overlap between the adjacent cylinders breathing through the same inlet.

If the porting is sufficient for both cylinders isnt it an advantage to have a more continous and less pulsing airflow through the carb venturi?

I was always struck by how small the venturi was on a single carburettor for a 6 cylinder engine compared to a 4 cylinder one and it would be a fraction of the surface area of 4 venturii on a twin webered engine.

Didnt they do something odd with webers on Mini engines back in the day where one venturi on each carb was blocked off?

The problem is the flow is still pulsing and that the second cylinder starts to draw before the first one has finished. This means that neither cylinder in the pair gets a full charge. Other factors like the more complex shape of the inlet tracts also means that the pulsing flow behaviour is harder to get optimum than a flow in a more simple straight tapering port.

You can certainly get away with a smaller single carb when its connected to something like a 6 cylinder engine as by the time you feed 6 cylinders up to a single carb any pulses are damped out in the manifold system

cheers
Rohan

Re: Minis and blocked-off Webers. According to then-current FIA regulations you could change the make but not the number of carburetters. Cooper S minis had 2 SUs as standard, so 1 DCOE would have worked technically but as 2 were required, 2 were fitted, each with one choke blanked off.

Thanks for that, I came across them on a lot of roadgoing cars but I guess the manifolds were available and people wanted to keep the race modified Cooper S look.