Reinforced exhaust valves Mazda MZR 2.5 L5-VE

Mazda engines covered

The L5-VE is the 2.5 litre of the MZR family: a naturally aspirated 2,488 cc four-cylinder with twin camshafts and 16 valves, fitted to the Mazda 3, Mazda 5, Mazda 6 and CX-7.

It has 8 exhaust valves, two per cylinder. The reinforced valves have a 5.48 mm stem and a 104.7 mm length, with a 30 mm head at standard size, 31 mm at +1 mm or 32 mm at +2 mm.

SUPERTECH reinforced exhaust valves

On a naturally aspirated engine, the metal of an exhaust valve head reaches 760 to 870 °C, and goes past 1,000 °C as soon as a turbo or supercharger is added. The head sheds about 75 % of its heat through the seat and 20 % through the guide. An EV8 family steel holds 550 MPa at 600 °C but drops to 300 MPa at 800 °C: the head distorts, fatigues and the seat ends up leaking.

SUPERTECH offers black nitrided stainless steel here, whose hardened surface limits stem wear in the guide, and Inconel, a nickel-based superalloy that keeps 860 MPa at 730 °C and 554 MPa at 815 °C, about 85 % more than the reference steel near 800 °C.

At +1 mm and +2 mm, only the head grows, to 31 then 32 mm: burnt gases escape more easily, with 10 to 12 cfm of flow gained per millimetre of head, provided the 8 exhaust seats are machined to the new diameter.

Exhaust valve technical specifications

MAEVN-2301F and MAEVN-2304F have a flat head; MAEVN-2301D and MAEVI-2306 a dished head. All four sets share the same 5.48 mm stem and 104.7 mm length.

Valve fitting

Before refitting the springs, check that the collets seat properly in the groove of the SUPERTECH valves and replace any that show marks.

MAEVN-2301F and MAEVN-2301D work with seats recut at standard size; MAEVN-2304F and MAEVI-2306 need seats machined to 31 or 32 mm.

Flat or dished, the head shape is chosen when ordering: fit the 8 valves of one shape on the engine.

Technical guide

Our brand

SUPERTECH Performance, a Californian maker of competition valves for more than thirty years, offers three black nitrided stainless steel exhaust valves for the MZR 2.5, at standard size and +1 mm, plus an Inconel version at +2 mm.

How to choose

Three criteria separate the four versions, size, head shape and material:

When reinforced valves become necessary

• Turbo or supercharger conversion (Inconel version recommended)
• Higher lift camshafts
• Track days or hill climbs
• Cylinder head rebuild with burnt or distorted exhaust valves

Vehicle compatibility

OEM part number (exhaust valve):

Don't forget the inlet valves

An MZR 2.5 cylinder head on the bench is the occasion to renew the inlet valves and the valve stem seals as well.