Reinforced exhaust valves BMW M50B25TU M52B25 M52B28 M54B25 M54B30

BMW engines covered

The BMW M50 in its VANOS variable valve timing version (M50B25TU, from September 1992), followed by the M52 (2.5 and 2.8 litre), the M52TU and the M54 (2.5 and 3.0 litre) are the 24-valve inline six-cylinder petrol engines fitted to the 3 Series (E36 and E46), 5 Series (E34, E39 and E60), 7 Series (E38 and E65), Z3, Z4, X3 and X5. The E36 M3 built for the North American market (S50B30US then S52B32US) use the same cylinder head.

Each engine is fitted with 12 bimetal exhaust valves with a 6 mm stem, BMW part number 11 34 1 739 823 (11 34 7 505 731 on the M54, same dimensions): 30.5 mm head, 6.0 mm stem, 105.7 mm length, held by 3-groove valve keepers. Designed for stock power, they are put to the test as soon as a build increases load, engine speed or exhaust gas temperature.

SUPERTECH and FERREA reinforced exhaust valves

The exhaust valve opens the path for burnt gases. Its head is hit by gases at 760 to 870 °C on a naturally aspirated engine, and above 1,000 °C on a forced induction engine, and only cools through contact with the seat and the guide. Yet steel quickly loses strength with heat: the steel head of the original bimetal valve loses nearly half of its strength between 600 and 800 °C. The higher the load, engine speed and boost pressure, the hotter it runs, the more it fatigues and the greater the risk of distortion and loss of sealing.

Reinforced valves use materials made for these temperatures: SUPERTECH high temperature steel and, above all, Inconel, a nickel-based superalloy that stays nearly twice as strong as steel at around 800 °C and above. FERREA states 20% more hot strength and 25% longer seat life for its Competition Plus valves. Three finishes are available for these engines: SUPERTECH black nitrided stainless steel, whose harder and smoother surface reduces friction and wear, SUPERTECH Inconel, recommended for forced induction, and FERREA hard chrome stems.

Exhaust valve technical specifications

FERREA: F1552P*12 and F1553P*12 not listed by the manufacturer for the S52B32US.

Valve fitting

The number of grooves on the valve and on the keepers must match: SUPERTECH specifies KPR-VW6-T keepers for its 3-groove valves and KPR-6S-7 keepers for its single-groove valves. A single-groove valve must never be fitted with the original keepers.

The +1 mm size increases the head diameter: it is fitted to a cylinder head whose seats have been machined to this size, a workshop job to plan alongside the cylinder head rebuild.

Technical guide

Our brands

SUPERTECH, a valvetrain specialist for more than three decades. Its valves are forged in one piece, coated with a black nitride treatment that hardens the surface and reduces friction, then inspected by ultrasound, X-ray and laser measurement, and designed using finite element analysis. The manufacturer develops its products with engine builders and chooses the material of each valve according to its use: stainless steel, Inconel, sodium-filled valves or titanium.

FERREA Racing Components designs its Competition Plus valves for high-revving, high-horsepower racing engines: slow two-step forging, 48-hour stress relief, hard chrome stem, hardened tip and undercut stem below the head (Super Flo design) for better gas flow. They are used by drag racing, oval track, road racing and sprint car teams, and each design is developed on the flow bench to balance flow, gas velocity and efficiency.

Standard size or +1 mm?

The standard size is fitted to a cylinder head whose seats are still at factory size. The +1 mm size is used when the seats need recutting: recutting widens the seat, and a larger head restores correct seat contact while increasing the flow area.

Single groove or 3 grooves?

3-groove valves keep the BMW design: their keepers do not clamp the stem, so the valve rotates and limits carbon build-up on its seat. This is the right choice for a road engine. On single-groove valves, the keepers clamp the stem tightly above and below the groove, which only locates them: the valve stays firmly held at high rpm and under high spring load, which is why they suit competition use. They are fitted with KPR-6S-7 keepers, 3-groove valves with the original keepers or KPR-VW6-T keepers.

When reinforced valves become necessary

• Camshafts with higher lift or stiffer valve springs
• Raised rev limit
• Turbocharger or supercharger added (Inconel version recommended)
• Cylinder head rebuild on a circuit, drift or rally engine
• Original valves marked, worn or already at repair size

Vehicle compatibility

OEM part number (exhaust valve): 11 34 1 739 823; 11 34 7 505 731 (M54B25, M54B30)

Don't forget the intake valves

A rebuilt cylinder head is fitted with new intake and exhaust valves, and with new valve stem seals. We offer the matching parts for these engines: