Thread: 15+inHG 400hp 350?

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There is only one way to get that kind of idle and that kind of hp and thats a roller cam. Comp's Xtreme Energy series are the next best thing in a flat tappet. The faster you can lift the valves off the seat, the higher your idle vacuum will be, but flat tappet cams are limited on lift rate. You'll have to use a dual plane manifold to get any reasonable amount of vacuum. GM's Vortec heads can support 400hp in stock or near stock form. You may have to change out sprins in order to accomodate the lift you want. GM sells the heads with the cut valve guides and improved springs, too.