Mike, the small diameter cross connection is not what has stirred my curiosity; rather it is the existence of the apparent intentional restriction of exhaust flow that is caused by the venturi in each pipe. The down pipes from the manifolds (entering from the right in the pic) have an ID of ~41mm, and the venturis an ID of ~31mm. Downstream (to the left in the pic) of the venturis the diffuser section opens the pipe ID again to 41mm. The cross sectional area of the choke of the venturi is ~57% of the area of the down pipe; to my mind, a significant restriction. Or is it? Exhaust pulses in each 3-cylinder manifold occur at 240 crankshaft degrees (relatively large spacing), and the area of the choke is approximately that of the smallest part of the exhaust port in the cylinder head. If the configuration is intended to result in a near constant back-pressure in each manifold/down pipe, is it for sound control purposes, or for control of valve overlap flow? If the latter, it is the only example this writer is aware of.