We showed a 14% gain in HP and almost 9% (8.8%) gain in torque at the factory with a taper bore 40/38mm. The venturi can somewhat be described as a keyhole design, however there is much more at work than just a big hole and little hole, annular disposition, laminar flow, etc. The taper bore is simply a 40mm front body attached to a full 38mm rear body. This again amplifies the signal to the metering rod with a little trade off in mass flow. The 40/38 moved the torque over to the left of the best 36mm Keihin tests, built power sooner and carried it longer past peak than the best 38mm settings. A straight 40mm made more power yet on top, but with a fair trade off on the bottom.
Corey
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