Reinforced exhaust valves Honda Prelude Accord H23A

Honda engines covered

The H23A is Honda's 2.3 litre four with 16 valves and twin overhead camshafts, in its non-VTEC version. It powers the Prelude IV 2.3 i 16V and the Accord V 2.3 i SR.

Its 8 exhaust valves, two per cylinder, carry the original part number 14721-PT2-000: 29 mm head and 6.6 mm stem. On this large-capacity four, they take hot burnt gases as soon as the engine is worked hard.

SUPERTECH reinforced exhaust valves

On a naturally aspirated engine, an exhaust valve head reaches 760 to 870 °C, and goes past 1,000 °C with a supercharger or turbo; this is the temperature of the metal. About 75 % of the heat leaves through the seat and 20 % through the guide. An EV8 family steel holds 550 MPa at 600 °C but drops to 300 MPa at 800 °C: the head overheats, distorts and sealing deteriorates.

The HEVN-1042D-8 is made of stainless steel with a black nitrided surface, a treatment that hardens the stem and limits wear in the guide.

It is +1 mm oversize: the head goes from 29 to 30 mm, with stem and length unchanged. Each millimetre of head adds 10 to 12 cfm of flow and burnt gases leave the chamber faster; the 8 exhaust seats are machined to that diameter.

Exhaust valve technical specifications

HEVN-1042D: 30 mm head (+1 mm), 6.5 mm stem, 102.7 mm length, black nitrided stainless steel.

Valve fitting

On reassembly, check that the collets lock properly into the groove of the new valves before releasing the springs.

The 30 mm head requires the 8 exhaust seats of the head to be machined; simple lapping is not enough.

Fit all 8 valves together and replace the exhaust valve stem seals at the same time.

Technical guide

Our brand

SUPERTECH Performance has been making valves and valvetrain parts for racing in California for more than thirty years. For the H23A it offers a +1 mm black nitrided stainless steel exhaust valve.

How to choose

Only one version exists for this engine:

When reinforced valves become necessary

• Cylinder head reworked for better flow
• Camshafts with more lift
• Track days or hill climbs
• Cylinder head rebuild with burnt or distorted exhaust valves

Vehicle compatibility

OEM part number (exhaust valve): 14721-PT2-000

Don't forget the inlet valves

An H23A cylinder head on the bench is the time to replace the inlet valves and the valve stem seals as well.