http://www.6thgenaccord.com/forums/showthread.php?t=49859 Look at the main post here - this is all you need to know (with pics) on the F20B...
VALVE SPECS (measured by me):
NOTE: H23A is the NON-VTEC, US-Spec 92-96 Prelude engine, not the Torneo/JDM H23 VTEC engine.
INTAKE VALVES (Face) (Length) (Stem Diameter) (OEM Honda Part Number):
F20B: 34mm (1.338"), 107.00mm (4.212"), 5.5mm (0.215"), 14711-PCB-000
H23A: 34mm (1.338"), 104.00mm (4.095"), 6.5mm (0.256"), 14711-PT2-000
H22A4:35mm (1.380"), 107.00mm (4.212"), 5.5mm (0.215"), 14711-P13-000
F22A1:34mm (1.338"), 112.00mm (4.410"), 5.5mm (0.215"), 14711-PT3-A00
EXHAUST VALVES (Face) (Length) (Stem Diameter):
F20B: 30mm (1.182"), 107.00mm (4.212"), 5.5mm (0.215"), 14721-PCB-000
H23A: 29mm (1.142"), 104.00mm (4.095"), 6.5mm (0.256"), 14721-PT2-000
H22A4:30mm (1.182"), 107.00mm (4.212"), 5.5mm (0.215"), 14721-P13-000
F22A1:29mm (1.142"), 124.000mm (4.882"), 5.5mm (0.215"), 14721-P0J-A00