Reinforced exhaust valves MINI Cooper S JCW N14 N18 Peugeot 207 308 EP6DT

MINI and Peugeot engines covered

The N14 and N18 are the 1.6 litre turbocharged 16-valve four-cylinders of the MINI Cooper S and John Cooper Works of the R55 to R61 generation, from 2006 to 2016: first N14B16A, N14B16AB and N14B16C, then N18B16A and N18B16C from 2010.

The EP6DT and EP6DTS are Peugeot's first 1.6 THP engines: turbocharged 16-valve four-cylinders fitted from 2006 to 2014 to the 207, 207 CC and 207 SW, then to the 308, 308 SW and 308 CC. The EP6DT produces 140 to 156 hp, the EP6DTS 174 hp in the 207 RC and the 308.

Each engine has 8 exhaust valves, two per cylinder. The original valve, shared by the N14 and the N18 (11 34 7 547 187), has a 26.0 mm head and a 4.96 mm stem; behind the turbo it works in very hot gases as soon as boost rises.

SUPERTECH reinforced exhaust valves

The exhaust valve opens into the burnt gases: its head reaches 760 to 870 °C on a naturally aspirated engine and exceeds 1,000 °C when turbocharged, these being metal and not gas temperatures. It cools mainly through the seat (nearly 75 % of the heat) and through the guide (about 20 %). An EV8 family steel holds 550 MPa at 600 °C but only 300 MPa at 800 °C: the head fatigues, distorts and the seal deteriorates.

SUPERTECH makes these valves in Inconel, a nickel base superalloy that keeps 860 MPa at 732 °C and 554 MPa at 816 °C, about 85 % more than EV8 family steel around 800 °C. The stem is hollow and sodium filled, carrying heat from the head to the guide; it measures 4.95 mm and has a single groove.

The MCEVI-1202-HS keeps the stem and length of the MCEVI-1200-HS, but its head grows from 26.2 to 27.0 mm: the flow area increases, burnt gases leave faster and the next filling benefits; the exhaust seats are then machined to this size.

Exhaust valve technical specifications

Both sets have the same 4.95 mm stem and the same 110.15 mm length; only the head differs.

Valve fitting

These single groove valves are fitted with KPR-5.0/7S collets.

The 4.95 mm stem slides in the valve guides: check their clearance during the rebuild and fit new valve stem seals (original 11 34 0 033 950).

The exhaust seats are reground with the new valves; for the 27.0 mm head they are machined to the new size.

Technical guide

Our brand

SUPERTECH, an American maker of racing valvetrain parts, offers two single groove Inconel exhaust valves with sodium filled stems for the N14 and N18: 26.2 mm head or enlarged 27.0 mm head.

How to choose

The two sets only differ by head diameter:

When reinforced valves become necessary

• Remap or bigger turbo (Inconel version)
• Track use
• Burnt or leaking exhaust valves
• Complete cylinder head rebuild

Vehicle compatibility

OEM part number (exhaust valve): 11 34 7 547 187

Don't forget the inlet valves

While the N14 or N18 cylinder head is off, also replace the inlet valves and the valve stem seals.