Reinforced inlet valves NISSAN RB25DET RB25DE RB25DEH

NISSAN engines covered

The RB25 is Nissan's 2.5 litre 24-valve inline six with twin overhead camshafts, naturally aspirated (RB25DE, RB25DEH) or turbocharged (RB25DET), from 179 to 280 hp. From 1989 to 2006 it powers the Skyline R32, R33 and R34, the Laurel C33, C34 and C35, the Cefiro A31, the Stagea WC34 estate and the Cedric and Gloria Y34.

Its 12 inlet valves come in two cylinder head generations: hydraulic tappets up to June 1997 (Nissan 13201-08U01, superseded by 13201-08U02, 13210-D4200 collets), then the NEO head with solid tappets and shims (13201-5L700, 13201-5L715 then 13201-5L716, 13210-53Y00 collets). More boost, sharper cams or a raised rev limit load them well beyond stock use.

SUPERTECH and FERREA reinforced inlet valves

The inlet valve lets fresh air in on every cycle, snaps back onto its seat and slides in its guide, dozens of times per second at high rpm. It runs between 400 and 550 °C: at 600 °C an original chrome-silicon steel only holds 250 MPa against 500 MPa at 500 °C, so half of its strength is lost (50 %).

SUPERTECH valves are made of black nitride stainless steel: the nitrided layer hardens the stem surface and reduces its wear in the guide. Their stem is relieved under the head (undercut) and their head has a back cut, two machining steps that clear the air path around the valve. The FERREA valves belong to the Competition Plus range, stainless steel with a chrome stem, which brings 20 % more hot strength and fatigue resistance and 25 % longer seat life. For the hydraulic tappet head, the FERREA valves of the same range are made of a special alloy.

The three SUPERTECH valves have a 35.15 mm head, the +1 mm oversize, with a 5.97 mm stem. For the NEO head, the FERREA valves come in standard size (34.15 mm head) and +1 mm oversize (35.15 mm), with a 5.98 mm stem and a length of 104.20 mm. A wider head enlarges the flow area at the seat: the cylinder fills better and the engine gains power, provided the 12 inlet seats are cut to this diameter. For the hydraulic tappet head, FERREA also supplies the standard size (34.12 mm head) and the +1 mm oversize (35.12 mm), with a 5.97 mm stem and a length of 86.70 mm.

Inlet valve technical specification

NIVN-1052-12: for hydraulic tappet heads; does not fit a NEO cylinder head.

NIVN-1052-NEO-12: for NEO heads with factory solid tappets.

NIVN-1052-SL-12: 16.8 mm longer, for a solid tappet conversion; groove placed 10 mm higher, 11.5 mm stem tip; does not fit a NEO cylinder head.

F1933P*12 and F1934P*12: for NEO heads, 6.25 mm stem tip.

F2151P*12 and F2152P*12: for hydraulic tappet heads, 3.5 mm stem tip.

Fitting details

The +1 mm oversize needs the inlet seats cut to 35.15 mm, workshop work to plan with the cylinder head rebuild.

The length follows the cylinder head: 86.75 mm (SUPERTECH) or 86.70 mm (FERREA) on a hydraulic tappet head, 104.15 mm (SUPERTECH) or 104.20 mm (FERREA) on a NEO head, 103.55 mm to convert a non-NEO head to solid tappets.

On a NEO head or one converted to solid tappets, check the clearance after replacing the valves and adjust the shims.

Technical guide

Our brands

	SUPERTECH Performance, based in San Jose, California, has been designing valves, springs and retainers for racing for more than three decades. Its parts are checked by ultrasound, X-ray and laser, and each part number is developed for a specific cylinder head together with racing engine builders.
	FERREA Racing Components was born in 1978 in Fort Lauderdale, Florida, started by two engine builders who came from Argentina. Each valve is forged in one piece from bar stock, then fully CNC machined; they are found in NASCAR and dragster engines.

How to choose

The cylinder head and the tappet type set the length; the size is then chosen according to the condition of the seats.

When reinforced valves become necessary

• Boost raised above the original value
• Sharper camshafts or stiffer springs
• Higher rev limit
• Cylinder head rebuilt for drift, circuit or rally
• Tired original valves or seats already reground

Compatible vehicles

OEM part number (inlet valve): 13201-08U01 / 13201-08U02 ; NEO : 13201-5L700 / 13201-5L715 / 13201-5L716

Related products

For a rebuilt RB25DET cylinder head, the reinforced exhaust valves are offered on these pages: