The Honda H22 is a very high performing engine in stock form, producing as much as 200 horsepower in the US production Prelude. The H22's performance can be further improved with the usual intake and exhaust breather modifications. Many enthusiasts go on to install upgraded cams or forced induction kits to their H22. However, if you want to get the most out of your naturally aspirated Honda H22 without modifying engine internals, modifying the stock intake manifold is a great upgrade to compliment other intake modifications, gaining as much as 15 horsepower on the H22.
Remove your H22's stock intake manifold by disconnecting all vacuum lines and sensors, as well as the throttle body bolts. Remove the intake manifold bolts from the engine head and the stock intake manifold will lift free, allowing for modification. Be sure to have a replacement intake manifold gasket for when you reinstall the intake manifold, as reusing old gaskets often leads to vacuum leaks.
Port your intake manifold runners by grinding away material from their interior surfaces with a die grinder. You want to keep the runners smooth and tapered, so grind delicately. Ideally, the intake manifold runners will perfectly match the ports they line up with on the engine head. For maximum performance gains, have your H22 engine head ported by a professional, then port-match your intake manifold runners to the modified engine head.
Port your intake manifold's inlet to match the diameter of the throttle body. Again, you want a smooth and even interior surface. For maximum performance gains, purchase a wider, aftermarket throttle body unit, then port-match the intake manifold's inlet to the increased throttle body diameter.
Purchase an aftermarket intake manifold if you don't wish to grind your stock unit. There are several aftermarket manufacturers who purchase bolt-on intake manifold kits for the H22. Alternatively, the intake manifold from the European Honda Accord R -- known commonly as the "Euro-R intake" -- is a popular upgrade for the H22 engine. These can be purchased direct from Honda Motor Co., or from various performance importers.
Reinstall your modified intake manifold to the H22 head in the opposite process of removal. Connect the manifold to the throttle body, and reinstall all stock vacuum lines and sensors. Start your vehicle and examine your modified intake manifold for leaks or malfunctions.
