Engine Valves

Leaking or worn valves, or a cylinder head that needs to handle higher revs and more boost? This category contains intake and exhaust valves in standard and oversize dimensions, as single valves or complete sets for your specific engine project.

What the valves do in the cylinder head

The intake valves let air and fuel into the cylinder, and the exhaust valves let the combustion gases out. They must seal against the valve seat at high temperatures while following the camshaft precisely at high revs. The exhaust side is typically the most heat-loaded, so material and design can vary between the two types. You can go directly to intake valves or exhaust valves.

How to choose valves

Start with the engine code, then compare the specific dimensions:

• Head diameter: standard size or oversize, e.g. +1 mm. Larger valves typically require machined valve seats, and the gain depends on the porting of the cylinder head.
• Stem diameter and length: must match the valve guides, springs and keepers.
• Material and load: high boost and high revs place different demands than a stock engine.
• Piston-to-valve clearance: must be checked, especially with a new camshaft or higher compression.

Examples in the category include Brian Crower valves in 30, 31, 35 and 37 mm, as well as Skunk2 sets for Honda/Acura K-series in standard size and +1 mm. Other brands include Ferrea, Supertech, GSC Power Division and Wiseco.

Installation and interaction with the valvetrain

New valves should be installed with suitable valve springs, retainers and keepers, and the valve seats typically need to be ground or cut so the seal is correct. Also check the valve guides for wear, and replace the valve stem seals at the same time. The work requires precise measurements, so many leave it to an engine builder.

Frequently asked questions

What does +1 mm mean on a valve?

It indicates that the valve head is 1 mm larger than the standard size. This can improve flow, but typically requires the valve seats to be machined, and the gain depends on the porting of the cylinder head and the rest of the engine.

Can I reuse the original valve springs with new valves?

It depends on the weight and dimensions of the valve as well as the camshaft you use. With heavier valves, higher lift or more revs, the original springs may be too weak, so check the manufacturer's recommendation for the specific set.

Why do the valve seats need to be machined when replacing valves?

New valves must seal tightly against the seat to maintain compression and conduct heat away. A leaking valve can cause loss of compression and overheating of the valve head, especially on the exhaust side.