The Offy port-o-sonic was different from the dual port, but looks the same from the outside. The port-o-sonic was a single plane, low profile design that relied on plenum volume, not runner length from carby, to distribute fuel evenly. It looks wrong but some reported good results. A dual plane Eddy performer would still out-do it. The Offy dual-port was a very interesting concept that didn't quite work. It was an attempt to create a dual mode high velocity/high flow design (in the smog era) by separating the primaries from the secondaries via a double-decker single plane design. It had the lower (primary) half of the manifold connected to the bottom portion of each split port, which was about half as big as the top portion. Low rpm, high velocity ports were supposed to allow better atomisation, then when the secondaries opened up, full flow from the top of each port would allow decent performance. Another aspect; the bottom half would be hotter from the oil vapour coming up from the engine, also promoting atomisation, and the top half would be insulated by the bottom. Unfortunately, it didn't catch on. The split in the ports was too restrictive for performance, ok they could be cut back and smoothed but even then it was only reasonable. Also in some designs (like the clevo), the front 4 cylinders starved due to the tight passages on the secondary side trying to get past the primary bores. Sent from my CPH1903 using Tapatalk