Reinforced inlet valves HONDA K20A2 K20A3 K20A8 K24A2

HONDA engines covered

The K20A2, K20A3 and K20A8 are Honda's 1,998 cc double overhead camshaft 16-valve VTEC four-cylinders; the K24A2 is the 2,354 cc version. They power the Civic VII (2.0 i Sport, Type-R EP3), the Integra DC5 and the Accord VII Tourer 2.4, from 155 to 200 hp, from 2001 to 2008.

Each engine has 8 inlet valves, two per cylinder, 109.1 mm long as standard and held by Honda 14781-PRB-A01 (K20A2) or 14781-PR7-A01 (K20A3, K20A8) collets. A sharper camshaft, stiffer springs, a higher rev limit or forced induction ask far more of them than stock use.

SUPERTECH reinforced inlet valves

On the inlet side, each valve opens and closes dozens of times a second at high rpm, strikes its seat and slides constantly in its guide, at 400 to 550 °C. At these temperatures the chrome-silicon steel of stock valves drops from 500 MPa at 500 °C to 250 MPa at 600 °C: it loses 50 % of its strength.

SUPERTECH makes these valves from an EV8-type racing stainless steel: 650 MPa at 500 °C and 550 MPa at 600 °C, i.e. 30 % then 120 % more than stock steel. Their black nitride treatment hardens and smooths the surface, which cuts friction and stem wear in the guide.

On top of the 35.0 mm standard size, SUPERTECH offers four oversizes of 35.5, 36.0, 36.5 and 37.0 mm (+0.5 to +2 mm), with the 5.48 mm stem and 108.85 mm length unchanged. The wider head lets more air through and improves filling, provided the inlet seats are cut to the new size. The 35.0, 35.5 and 36.0 mm sizes come with a flat or dished head, the 36.5 and 37.0 mm sizes with a flat head.

Inlet valve technical specification

Dished heads: HIVN-1020D-8, HIVN-1021D-8, HIVN-1022D-8. Flat heads: HIVN-1020F-8, HIVN-1021F-8, HIVN-1022F-8, HIVN-1022.5F-8, HIVN-1023F-8; HIVN-1023F-8 with back cut.

Fitting details

The +0.5 to +2 mm oversizes require the inlet seats to be cut to the diameter of the chosen head, from 35.5 to 37.0 mm, workshop work to plan with the cylinder head rebuild.

Valve clearance is set by adjusting screws on these engines: after replacing the valves, check and set it (0.21 to 0.25 mm cold on the inlet side on the K20A2 and K20A3).

Technical guide

The brand offered

SUPERTECH, based in San Jose, California, has designed valvetrain parts for racing engines for more than 30 years: valves, springs, retainers, guides. Each valve is drawn for a given cylinder head, checked by ultrasound, X-ray and laser, then proven with engine builders, at the drag strip as on the circuit.

How to choose

The size depends on the condition of the inlet seats in the cylinder head and the airflow gain wanted.

When reinforced valves become necessary

• Higher-lift camshafts or stiffer springs
• Raised rev limit
• Turbo or supercharger fitted
• Cylinder head rebuilt for circuit, hill climb or rally
• Original valves marked, worn or already reground

Compatible vehicles

OEM part number (inlet valve): 14711-PRB-A01 (K20A2); 14711-PNL-E00, 14711-PNA-000 (K20A3); 14711-PNA-000 (K20A8)

Related products

A rebuilt K20A or K24A2 cylinder head also takes new exhaust valves, available on this page: