Due to the shape and casting method of the M20 intake manifold, extrude honing offers a significant performance increase. Up to 15 HP gains on modified intakes can be expected. Although not cheap, this modification offers a good bang for the buck.
Note on core/exchange charge: You can ship us your intake manifold, or we'll provide a core manifold. Figure 2-3 weeks turnaround for this procedure. Your core charge will be refunded upon receipt of your good intake manifold.