Russ and Jac,
I think I might have unintentionally confused you regarding the runner lengths. In an IR intake system, the cylinder “sees” the combined length of the cylinder head intake port, intake manifold runner, carb venturi, trumpet, along with any/all gaskets, spacers or isolators as the functional resonating length. In my client’s original system (show here sans cylinder head) that total was 17.4 inches, which was way wrong on several counts for the intended application…the refraction wave arriving back at the cylinder during the overlap period only from 5300 through about 6400 RPM, and then not again until 8600 RPM, which is not only past the limits my client would prefer to stay within, but during the span between is actually a substantial detriment to power production.
In the new design shown below, the plenum chamber (rather than the end of the carb trumpet) provides a pressure boundary to initiate the refraction wave movement back toward the cylinder, causing the cylinder to “see” an effective length of 8.9 inches. This system effectively “tunes” twice during the engine’s operating range, with the effect peaking the first time (4th order resonance) at 6500 RPM and then again (3rd order) at 7900. Hopefully, my fellow engineers/racers here will forgive me the weight of the substantial bracing; these trucks often are subjected to vertical stress akin to driving off the roof of a house during competition. I’ll be machining the manifold from billet 6061 T-6 in two pieces as shown, then welding the plenum “end”/carb mounting plate on before taking a final light cut to true any warpage.
Also Russ, here is a pic of the isolators and the O-ring style gaskets that the original system used. From your description, I’m fairly sure that the gaskets (which appear to be Redline pieces) are what you are referring to. If you’ve found these by themselves to be effective at reducing fuel frothing in the past, then I feel a bit better about omitting the larger (and much heavier) isolators from the new system.
