Understanding intake manifold principles.

[Bret Williamson]

Hi there, hope someone is able to help me. I am trying to find some info on early intake manifold designs, for Ford 4 cylinder engines, otherwise known as the T-, A- and B- engines. These engines came standard with two intake manifold inlets, and 4 exhaust manifold outlets cast into the block.
I have found lots of pictures of after-market dual-carburettor manifolds. These used dual intake runners, with two general systems. In the first system, the carburettors mounted on a common plenum, which then opened into the intake runners. In the second system, the carburettors were mounted at the top of the intake runner, with a cross-over pipe linking the intake runners.
Does anyone know the theory behind this cross-over pipe, or seeming balancing of the intake runners? Is one more effective than the other? Can anyone point me to a source that might explain the principles?
Cheers
Bret W.

 

[brewnog]

Sounds like it's just a balancing pipe, equalising pressure in the runners to ensure that the cylinders are inducing the same quantity, and mixture, of inlet charge.

Do you have any pictures of the arrangements?

 

[NoTime]

Don't know the Ford engines, but I've dealt with separate plenum systems on other engines.
It was a real headache to syncronize the carbs.

Perhaps the crossover was intended to reduce the syncronization problem as brewnog suggests.

 

[brewnog]

I've got a Ford engine (1960s design) using two twin-choke carbs, so there is a plenum for each pair of cylinders. As a result, cylinders 1 & 2, and cylinders 3 & 4 are balanced, but it can be quite a pain to balance the two pairs. The original carburettor on the engine had a single plenum, and single carb feeding all four cylinders on a common manifold. Much easier to set up, but not nearly the same flow.

 

[Bret Williamson]

I think you are on to something there brewnog. I seem to remember reading something similar about crossover pipes in exhaust systems blancing the pressure.

I am planning to build a dual-carb manifold, but thought i would try to understand the principles before i added anything to the design unnecessarily! Like i said, a lot of the aftermarket stuff was twin-carb items, most developed in the 30's, 40's and 50's, when there wasn't a wide range of different flow-rate carbs to choose from, like we have today. So, those clever guys realising that the more air/fuel mix available, the more potential energy, started adding multiple carbs.
So, my aim is to emulate that basic idea, but using more modern (60's) carburettors.

 

[brewnog]

Mmm, twin choke Weber DCOEs maybe?