B-Series Intake Manifolds
 MGB MGA

Not so!!
Certainly anything except an all out high RPM race engine needs some sort of balance pipe between the two runners to ensure a smooth idle and cruise.
Unfortunately the huge cross-over the factory  put in causes a major disruption to the flow that is trying to get into the port.
This flow disruption is so bad, that the high speed air which is normally at the top of the port in the head is now at the bottom. This causes major turbulence and flow reduction when it gets towards the valve seat. The reason being that the short side turn into the cylinder requires the air speed to be slower to make this abrupt turn with any reasonable success, and the long side more gentle turn (spark plug side) can accommodate higher speed air.
However, what we have in this situation is the exact opposite of what works best.

Maniflow make tubular-Steel twin SU intake manifolds with a small diameter cross over tube located in a much less 'airflow critical' portion of the port runner.
This allows the balance required as mentioned above, but does not cause the turbulent airflow eddies that the stock manifold suffers from.

We have been seeing a consistent 4 - 5 HP gain on both 'A' & 'B' series engines using the Maniflow intake manifold compared to the stock factory supplied version.