Reinforced exhaust valves BMW B48B20 B48A20 B46A20

BMW engines covered

The B48 is the 1,998 cc turbocharged four-cylinder of the BMW modular family (82 mm bore, 94.6 mm stroke), built since 2014; the B46 takes the same exhaust valve. It is found in the 120i, 125i, 220i, 230i, 320i, 330i, 420i, 430i, 520i, 530i and the Z4 20i and 30i.

Its 16 valve cylinder head has 8 exhaust valves, with a 6 mm stem and a single groove. A simple remap greatly increases the boost pressure of this engine, and with it the temperature its exhaust valves have to withstand.

SUPERTECH reinforced exhaust valves

On a turbocharged engine, the exhaust valve opens into gases that then head for the turbine: the metal of its head goes beyond 1,000 °C there, where a naturally aspirated engine stays between 760 and 870 °C. It removes this heat about 75 % through its seat and 20 % through its guide. EV8 family steel, used as a benchmark, drops from 550 MPa at 600 °C to 300 MPa at 800 °C.

Both SUPERTECH valves on this page are Inconel, a nickel superalloy that holds 1,100 MPa at 649 °C and 554 MPa at 816 °C, about 85 % more than EV8 steel around 800 °C, with a hollow sodium filled stem that, liquid from 97.8 °C, carries heat from the head to the stem.

The MCEVI-1401S-HS takes the head from 28.5 to 29.5 mm: the larger flow area speeds up the gases towards the turbo and improves scavenging, with a power gain; the exhaust seats are then cut to this size.

Exhaust valve technical specifications

The KPR-6S/7 collets are fitted with the original retainers and springs.

Valve fitting

Both part numbers have a single groove; they are fitted with KPR-6S/7 exhaust collets and VSI-BM60-E valve stem seals.

The MCEVI-1400S-HS keeps the 28.5 mm head and the seats as they are; the 29.5 mm MCEVI-1401S-HS requires the exhaust seats to be cut.

The set of 8 matches the 8 exhaust valves of a four-cylinder.

Technical guide

Our brand

SUPERTECH Performance has been designing racing valvetrain parts in California for more than thirty years. For the BMW B38, B48 and B58 modular engines, it offers sodium filled Inconel exhaust valves, at standard size or 1 mm larger.

How to choose

The two versions differ only in head size:

When reinforced valves become necessary

• Remap with higher boost pressure (Inconel version recommended)
• Larger or hybrid turbocharger
• Modified camshafts or valve springs
• Track use
• Marked original valves during a rebuild

Vehicle compatibility

OEM part number (exhaust valve): 11 34 8 621 264

Don't forget the inlet valves

For a fully rebuilt B48 cylinder head, also plan the inlet valves: