Supertech Inconel Forged Exhaust Valves for N14 & N18 MINI

Supertech Inconel Exhaust Valves are engineered for the extreme thermal and mechanical demands of high-performance Gen 2 MINI N14 and N18 engines. Produced from Nimonic 751 Inconel alloy, these valves deliver exceptional resistance to heat, creep, and oxidation. Valves becoming burnt can be issues in tuned MINIs where exhaust gas temperatures can soar well beyond safe limits for OEM valves especially when output is sustain, for example on circuit. The Supertech CNC optimised profiles further enhance exhaust flow, improving turbo efficiency, combustion stability, and overall power delivery.

Forged rather than cast, Supertech valves feature a refined grain structure that makes them significantly stronger and lighter than factory components. Reduced valve mass allows improved valvetrain stability at high RPM, minimises the risk of valve float, and reduces stress on springs and followers—critical for R55, R56, and R57 MINIs running increased boost or upgraded turbochargers. We would recommend coupling the valves with the Supertech Beehive springs and titanium retainers for maximum benefit in these areas. 

Lohen offer 2 sizes of the Supertech Inconel exhaust valves:

Standard Size

• Direct replacement diameter, but with a re-profiled head shape to improve exhaust gas flow over OEM valves.
• Even at the standard size, the upgraded valve shape requires new valve seats to be cut, as the seat contact and flow-optimised geometry differ from the stock MINI design.
• Ideal for builds focused on durability and reliability without altering combustion chamber geometry.

2. +0.8 mm Oversize

The enlarged valve head increases curtain area, the effective flow area around the valve when open.

This improves exhaust scavenging, reduces backpressure, and enhances turbo spool characteristics.

Particularly beneficial for engines running: 

• Larger or hybrid turbochargersIncreased boost pressure
• High-lift camshafts Aggressive ignition and fuel strategies
• Oversize valves require machining the cylinder head to accept new, larger valve seats, enabling the increased flow potential without compromising sealing.

The +0.8 mm option is recommended for those seeking maximum airflow efficiency and improved high RPM performance, where every incremental flow gain contributes to power and thermal stability.

Why New Valve Seats Are Required for Both Sizes

Regardless of whether you choose the standard or oversize diameter: 

• The Supertech valve profile is designed to improve gas flow and differs from the OEM valve seat geometry.
• For proper sealing, longevity, and performance, new valve seats must be cut to match the valve’s specific contact pattern and optimised flow shape.
• Failure to recut seats can lead to improper sealing, reduced compression, inefficient exhaust flow, and potential premature valve wear.

This machining step ensures the upgraded valves deliver their full reliability and performance benefits.

When Should Supertech Inconel Exhaust Valves Be Installed?

We recommend upgrading when your MINI’s engine output exceeds 250 hp, as OEM valves are prone to thermal distortion, burning, and failure at these power levels. They are strongly advised for: 

• High-boost or big-turbo builds
• Track-driven MINIs exposed to sustained high Exhaust Gas Temperatures (EGTs)
• Fully forged engine builds JCW and Cooper S engines pushing beyond factory tolerances
• Any driver prioritising long-term durability in a tuned N14 or N18 engine

Lohen offers professional, in-house fitting for all products at our workshop in Eccleshall, Staffordshire, ST21 6JL. Here are the important things you need to know:

Fitting Cost - Engine build costs start from £699; talk to our team to discuss your options, please call +44 (0) 1785 85 99 99. 

Fitting Time - From 2 days for engine builds

Required Additional Items/Services - Single groove valve keepers - 2 are required per valve. For example 8 exhaust valves require 16 single groove valve keepers. 

Lohen Recommends - Titanium valve springs to improve valve operation rate. 

Q. Do I need titanium valve springs with these valves?
A. No, but titanium valve springs improve the return rate of valves allowing them to operate quicker than valves running with standard valve springs. Ideal for highly tuned MINIs. 

Q. Are inlet valves available in the Inconel alloy too?
A. No, there's no need for the Inconel alloy to be used here because temperatures are not as high as the exhaust side. Supertech Intake Stainless Steel Nitride-coated Valves are sufficient.