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The old combo paired the LS6 intake manifold with 36-lb/hr injectors (the smaller of the two) originally meant for a Buick Grand National. One for the L92 is from an LS3 and rated at 39 lb/hr. Fitting them to the Holden L76 (or FAST) intake manifold requires O-rings of a different size. Thus, the difference of inside diameters on the LS6/FAST 0.540-inch injector boss and the LS2, LS3, LS7, and L76 0.565-inch boss creates a sizable vacuum leak. You cannot swap the lower injector O-rings for stock late-model pieces as the inside diameter of the manifold bung is also different and will result in escaping vacuum.