Reinforced inlet valves MAZDA MZR 2.3 DISI turbo L3-VDT

MAZDA engines covered

The L3-VDT is Mazda's 2.3-litre MZR DISI: a turbocharged direct-injection four-cylinder with 16 valves. From 2004 to 2014 it powers the BK and BL generation Mazda 3 MPS, the four-wheel-drive Mazda 6 MPS, the CX-7 and the MPV III, with 238 to 277 hp depending on version.

The engine has 8 inlet valves, two per cylinder. A remap, raised boost or sharper camshafts expose them to far more heat and impact than the standard engine.

SUPERTECH reinforced inlet valves

On this boosted engine every inlet valve admits the charge forced in by the turbo, shuts with a sharp blow and rubs continuously against its guide bush. Running at 400 to 550 °C, it puts ordinary chrome-silicon steel under strain: 500 MPa at 500 °C, then only 250 MPa at 600 °C, a 50 % drop. Extra boost and higher revs make the job harder still.

SUPERTECH shapes it from stainless steel and then gives it a black nitride treatment, which hardens the surface and protects the stem from galling in its guide; the head is dished and relieved underneath and on the back, and the 6 mm stem ends in a tapered tip.

Inlet valve technical specification

MAIVN-2301D-6MM-8: set of 8 valves at the maker's standard size, dished head, thinned under the head and profiled on the back.

Fitting details

The GDE-DUR16-6MM-8*2 bronze guides are made for the 6 mm stem of this engine, on both the inlet and exhaust side.

At standard size the valve sits on the factory inlet seats; lapping or a light recut is enough during a rebuild.

Technical guide

The brand offered

SUPERTECH Performance, a Californian firm, has now spent thirty years concentrating on racing valvetrain hardware. Before shipping, every batch goes through an ultrasonic check, an X-ray and a laser measurement, then leaves for engine builders active in competition.

How to choose

Only one set exists for the L3-VDT; at factory diameter it fits without any seat work and stands out mainly for its steel and surface treatment.

When reinforced valves become necessary

• Sharper cam profiles, stiffer valve springs
• Boost and red line raised by a remap
• Larger turbo fitted to the MZR DISI
• Head prepared for circuit racing or rallies
• Tired factory valves or valves marked by carbon build-up

Compatible vehicles

Don't forget the exhaust valves

When the L3-VDT head is off, replace the 8 exhaust valves too and, if needed, the bronze guides; both are offered for this engine here: