Reinforced exhaust valves Honda Civic Integra Accord K20A K24

Honda engines covered

Honda's K series brings together the 1,998 cc K20A (86 mm bore and stroke) and the 2,354 cc K24 (87 mm bore, 99 mm stroke), two four-cylinder engines with twin camshafts and 16 valves. From 2001 the K20A powers the Civic VII and VIII, including the EP3 Type R, and the DC5 Integra; the K24A is fitted here to the Accord VI Aerodeck and VII.

Each cylinder head carries 8 exhaust valves. On the K20A2 of the EP3 Civic Type R, the original 14721-PRB-A00 valve has a 30.2 mm head, a 5.5 mm stem and a 108.7 mm overall length; two 14781-PRB-A01 collets hold it. The longer the engine stays high in the rev range, the hotter this valve runs.

SUPERTECH and FERREA reinforced exhaust valves

The exhaust valve lets the burnt gases out and therefore sits in the hottest flow in the engine: its head reaches 760 to 870 °C on a naturally aspirated engine and 1,000 °C or more with forced induction, measured in the metal. About 75 % of this heat goes through the seat and 20 % through the guide. The original steel is rated with the values of an EV8 family steel: 550 MPa at 600 °C and 300 MPa at 800 °C. An overworked head fatigues, warps and then lets compression escape.

SUPERTECH offers the K20A valve in three materials: black nitrided stainless steel (HEVN), whose nitrided layer protects the stem against wear; Inconel (HEVI), a nickel-based superalloy that keeps 860 MPa at 732 °C and 554 MPa at 816 °C, around 85 % more than the original steel near 800 °C, the material to choose for forced induction; titanium (HEVT), 1.9 mm shorter than standard. FERREA offers three ranges: Competition Plus, in stainless steel with a chrome stem, with 20 % more hot strength and 25 % longer seat life, 6000 series in EV8 stainless steel and 5000 series in stainless steel with a hard chrome stem.

The +0.5, +1 and +1.5 mm sizes enlarge the head only, up to 31.5 mm: the burnt gases leave faster and scavenging improves, by about 10 to 12 cfm of flow per millimetre of head. The exhaust seats are then machined to the chosen diameter.

Exhaust valve technical specifications

Valve fitting

All valves on this page have a single groove: they are fitted with single groove collets, such as the K10034.

At 30 mm the seats stay as they are; at 30.5, 31 or 31.5 mm, the 8 exhaust seats are cut to the diameter of the new head.

As the titanium valves are 1.9 mm shorter than standard, their fitting is prepared with the cylinder head off. For valve stem seals, Honda fits the PZ1 part numbers on the K20A2 (12210-PZ1-003 / 12211-PZ1-003, then -004) or 12211-P45-G01.

Technical guide

Our brands

	SUPERTECH Performance, based in California, has been producing racing valves for more than thirty years. For the K series its range goes from black nitrided stainless steel through Inconel to titanium, from standard size to +1.5 mm.
	FERREA, founded in 1978, makes its valves in Florida and Argentina. For the K20 it offers three stainless steel ranges, Competition Plus, 6000 and 5000, in standard size and +1 mm.

How to choose

All these valves have a single groove: the choice comes down to size, material and engine:

When reinforced valves become necessary

• More aggressive camshafts or uprated springs
• Engine often taken to the limiter
• Turbo or supercharger (Inconel version recommended)
• Track days
• Cylinder head rebuild with pitted or warped exhaust valves

Vehicle compatibility

OEM part number (exhaust valve): 14721-PRB-A00 (K20A2, EP3 Civic Type R)

Don't forget the inlet valves

When the cylinder head of a K20A or K24 is off, take the opportunity to check the inlet valves and the valve stem seals.