Reinforced inlet valves BMW B38A15 B38B15

BMW engines covered

The B38 is BMW's 1.5 litre turbocharged three-cylinder, with roller finger followers, hydraulic lash adjustment and Valvetronic variable lift on the inlet side. Fitted lengthways (B38B15) or transversely (B38A15), it has powered the 1 to 4 Series, the Active Tourer and Gran Tourer, the X1 and X2 since 2014, from 102 to 326 hp depending on version, hybrids included.

Its 6 inlet valves are BMW 11 34 7 633 699: 30.1 mm head, 5 mm stem, held by 11 34 1 438 142 collets. A remap that raises boost pressure exposes them to more heat and harder impacts.

SUPERTECH reinforced inlet valves

On the three-cylinder B38, the inlet valve keeps time with the cam: at high revs it steps aside dozens of times a second to fill the chamber with air pushed by the turbo, snaps straight back onto its seat, and its stem never stops rubbing in the guide. It handles 400 to 550 °C, and the chrome-silicon steel chosen by the maker soon loses ground at that level: 500 MPa at 500 °C, only 250 MPa at 600 °C, a drop by half. Every extra millimetre of lift, harder spring, rev or bit of boost adds to the hammering, wear and heat.

SUPERTECH produces these valves in a race-grade chrome-nickel stainless from the EV8 line: 650 MPa at 500 °C, a 30 % reserve over the original metal, and 550 MPa at 600 °C, a 120 % reserve. The black nitride coat makes the metal's skin harder and more slippery, so the stem stands up better to contact with the guide.

Sizes stay as the maker set them: 30.1 mm head, 5 mm stem, a single groove. The cylinder head seats are kept as they are, with no move to a new size.

Inlet valve technical specification

MCIVN-1400S-6: dished head, to be fitted with KPR-5.0-7S collets.

Fitting details

The SUPERTECH valve has a single groove: it is fitted only with KPR-5.0-7S collets, never with the original ones.

The original size is kept: the inlet seats are checked and refreshed as usual during the cylinder head rebuild.

Clearance is taken up hydraulically: no adjustment is needed after replacing the valves.

Technical guide

The brand offered

SUPERTECH, a Californian maker established in San Jose, has been developing competition engine valvetrains for over 30 years. Its valves are worked out one by one for the target engine, inspected by ultrasound, X-rays and laser, then validated in the field by tuners.

When reinforced valves become necessary

• More aggressive camshafts or uprated return springs
• Ignition cut set higher
• Enlarged turbocharger or raised charge pressure
• Head restored for track, drift or stage use
• Factory valves damaged, worn out or refaced before

Compatible vehicles

OEM part number (inlet valve): 11 34 7 633 699

Related products

With the B38 head already off, it makes sense to swap the exhaust valves too, within one single strip-down. Corresponding parts are offered here: