Reinforced exhaust valves Nissan Skyline Laurel Stagea RB25DET

Nissan engines covered

The RB25DET is Nissan's 2.5 litre turbocharged straight six with 24 valves. It is found in the Skyline R33 and R34, the Laurel C34 and C35, the Stagea estate and the Cedric and Gloria Y34 saloons.

Its cylinder head carries 12 exhaust valves. The reinforced standard-size valve has a 29.6 mm head, a 5.96 mm stem and an 88.95 mm overall length. The turbo keeps these valves in very hot gases as soon as boost rises.

SUPERTECH and FERREA reinforced exhaust valves

On the RB25DET, the turbo plunges the exhaust valves into very hot gas as soon as boost climbs. Measured in the metal, their head then exceeds 1,000 °C, whereas an unboosted engine stays at 760 to 870 °C. The seat drains roughly 75 % of that heat, the guide some 20 %. Taken as the reference, an EV8-family steel keeps 550 MPa at 600 °C, but no more than 300 MPa at 800 °C. With every rise in boost, revs or load, the head runs a little hotter, fatigues, distorts and ends up leaking.

Hence the switch to nickel superalloys. SUPERTECH offers its NEVI-1052 in Inconel, a material that holds 860 MPa at 730 °C and 554 MPa near 815 °C, close to 85 % better than EV8 steel around 800 °C, in three lengths: 89.0 mm, 97.6 mm for the NEO and 105.8 mm for the SL, meant for solid tappets. FERREA answers with the Super Alloy of its Competition Plus series, also nickel-based and designed for turbo use, which the maker credits with a 20 % gain in strength at temperature and 25 % more seat life. Both materials share one aim: keeping their strength where the original steel gives up.

The 1 mm oversize versions take the head to 30.6 mm from FERREA and 30.7 mm from SUPERTECH; stem and guide are unchanged. The chamber empties faster, fresh air flows in more freely and output benefits, while every other part stays as it is. All 12 exhaust seats must then be cut to that new diameter.

Exhaust valve technical specifications

The F2149P is at standard size and the F2150P at +1 mm oversize, both intended for turbocharged engines. The three NEVI-1052 are +1 mm oversize; the NEVI-1052-SL, 105.80 mm long, is 16.8 mm longer for fitting with solid tappets, with the groove placed 10 mm higher (11.5 mm stem tip).

Valve fitting

Compare the valve lock groove with the collets you reuse before refitting the springs.

At 29.6 mm the seats stay as they are; with a +1 mm version, the 12 exhaust seats are cut to the size of the new head.

The NEVI-1052-SL, 16.8 mm longer, is reserved for a cylinder head converted to solid tappets; the other part numbers keep a length close to standard.

Technical guide

Our brands

	SUPERTECH came to life in Silicon Valley and specialised more than 30 years ago in valvetrain parts for racing: valves and springs, but also guides and titanium retainers. The maker studies each model around one specific engine and has it validated on track by seasoned, well-known tuners.
	FERREA Racing Components owes its birth, in 1978, to Horacio Ferrea and Daniel Urrutia. Based in Florida and Argentina, the firm shapes stainless steel, titanium or superalloy valves that engine builders all around the world install in their racing engines.

How to choose

Compressed by the retainer, the collets anchor onto the valve stem. Here the choice is between two head sizes and two materials; length, for its part, depends on the type of tappets fitted to the cylinder head.

When reinforced valves become necessary

• Turbo boost raised or bigger turbo (Inconel version recommended)
• More aggressive camshafts or stiffened valve springs
• Cylinder head converted to solid tappets (SL version)
• Track or drift days
• Head to redo, exhaust valves marked or burnt

Vehicle compatibility

OEM part number (exhaust valve): 13202-08U01; 13202-5L715 (from 06/1999)

Don't forget the inlet valves

An RB25DET cylinder head on the bench is the chance to renew the inlet side and the exhaust stem sealing at the same time. The parts designed for this engine: