You most certainly can bolt up a 2g intake manifold onto a 1g head. What you wouldn't want to do would be to put a 1g intake manifold on a 2g head, as the port holes are bigger on the manifold. This is not an issue with a 2g manifold on a 1g head because the 2g is smaller. Are flowing from a smaller space to bigger one is happy air, while are flowing from a larger space to a smaller space is sad (for what should be obvious reasons).

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