Reinforced inlet valves SUBARU EJ251 EJ253

SUBARU engines covered

The EJ251 and EJ253 are Subaru 2.5 litre flat-four (boxer) engines with 16 valves and one camshaft per cylinder head, operating the valves through rocker arms. From 1999 to 2011 they power the European Forester SG and SH, Impreza GD, GG and GE, Legacy III and IV and Outback BH and BP, with 152 to 177 hp.

The engine has 8 inlet valves, two per cylinder. Subaru part numbers are 13201AA361, then 13201AA362 on the EJ253 from 2006, with a length of 120.6 mm; they are held by 13210AA020 collets. Tuning with more revs, sharper camshafts or a turbo loads them far beyond what the factory design expects.

SUPERTECH reinforced inlet valves

In this boxer, each inlet valve is pushed open by a rocker arm to let the mixture in, then snaps back and hits its seat on every cycle, while the stem moves up and down in the guide. Each cylinder has two of them, eight for the engine. Its working temperature sits between 400 and 550 °C, a range where factory chrome-silicon steel weakens clearly: its strength halves, 50 % less, from 500 MPa at 500 °C to 250 MPa at 600 °C. Higher revs, firmer springs or added boost make this work even harder for the original part.

For these EJ25 engines, SUPERTECH uses a racing grade chrome-nickel stainless steel of the EV8 (21-4N) family: at 500 °C it still holds 650 MPa, 30 % better than the original steel, and at 600 °C 550 MPa, 120 % more. Its stem is chrome plated, a finish that protects the surface rubbing in the guide and helps it slide when the engine revs high and runs hot.

This part comes as a +1 mm oversize: the head grows to 37 mm, while the 5.96 mm stem and 120.6 mm length stay those of the original part. With this larger section at the seat, each cylinder breathes in more air and the engine makes more power, as long as the inlet seats of both heads have first been machined to this new dimension. The stem tip measures 5.0 mm.

Inlet valve technical specification

SIVN-1025-8: set of 8 valves, 5.0 mm stem tip.

Fitting details

No reinforced collets or valve stem seals are listed for these engines: the Subaru parts shown above are refitted, preferably new.

The 37 mm head needs inlet seats cut to this size. Valve clearance is set with screws on the rocker arms: 0.20 mm on the inlet side, engine cold (tolerance ± 0.02 mm on the EJ251 and ± 0.04 mm on the EJ253), to be checked after replacement.

Technical guide

The brand offered

Working out of San Jose in California, SUPERTECH has spent over thirty years designing valvetrains for race engines. Every engine gets its own valve drawing, checked by ultrasonic inspection, radiography and laser gauging, then validated in competition tuners' engines.

How to choose

These engines get one set here: its larger head and its finish decide the work needed on the head and the gain compared with the Subaru part.

When reinforced valves become necessary

• Sharper cam profiles or firmer valve springs
• Rev limit raised
• Turbo or supercharger fitted to the naturally aspirated boxer
• Head rebuilt for rally, track or hill climb
• Worn or marked Subaru valves, or seats already reworked

Compatible vehicles

OEM part number (inlet valve): 13201AA361 / 13201AA362

Don't forget the valve springs

When a rebuilt head goes back on, new valves work better with springs in good shape; a reinforced kit made for these engines is available here: