Reinforced inlet valves HONDA K24Z3 K24Z7

HONDA engines covered

The K24Z3 and K24Z7 are Honda 2.4-litre double overhead camshaft 16-valve VTEC four-cylinders, from 188 to 206 hp. They are found in the Accord VIII and IX 2.4, the Civic IX 2.4 and the CR-V III and IV 2.4, from 2007 onwards.

Each engine has 8 inlet valves, two per cylinder, held on the K24Z3 by Honda 14781-RGM-A01 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 these engines SUPERTECH takes 36.0 mm as the standard size and offers two oversizes of 36.5 and 37.0 mm (+0.5 and +1 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 standard size comes with a flat or dished head, the oversizes with a flat head.

Inlet valve technical specification

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

Fitting details

The +0.5 and +1 mm oversizes require inlet seats cut to 36.5 or 37.0 mm, workshop work to plan with the cylinder head rebuild.

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-R44-A00, 14711-R40-A00 (K24Z3)

Related products

For the same cylinder head, the reinforced exhaust valves for the K24Z3 and K24Z7 are on this page: