Reinforced exhaust valves Mitsubishi 3000 GT 6G72

Mitsubishi engines covered

The 6G72 is the Mitsubishi 3 litre V6; in its twin-cam, 24-valve form it powers the 3000 GT, naturally aspirated (Z11A) or twin-turbo with four-wheel drive (6G72-T, Z16A), sold in Japan as the GTO.

The engine has 12 exhaust valves with a 6.5 mm stem, part number MD183730 on the twin-turbo and MD135480 on the naturally aspirated engine, with a 30.5 mm head and a 105.4 mm length. On the twin-turbo they take particularly hot burnt gases as soon as boost rises.

SUPERTECH and FERREA reinforced exhaust valves

During its opening phase, the 6G72 exhaust valve releases gases fresh from combustion into the manifold, then into the turbos on the twin-turbo version. Taken in the metal, its head stays near 760 to 870 °C on the naturally aspirated 3000 GT and climbs past 1,000 °C on the twin-turbo. About 75 % of its heat flows out through the seat and close to 20 % through the guide. Used as a yardstick, an EV8 valve steel retains 550 MPa near 600 °C but only 300 near 800 °C. When turbo boost, revs or load rise, the head heats up further, wears through fatigue, buckles and no longer seals the cylinder.

To cope, reinforced valves change material. FERREA supplies its Competition Plus range here in Super Alloy, a nickel-based alloy which the brand credits with 20 % additional thermal strength and a seat that wears 25 % more slowly, in standard size or +1 mm. SUPERTECH relies on Inconel, a nickel superalloy keeping 860 MPa at 730 °C and still 554 MPa around 815 °C, roughly 85 % more strength than EV8 steel at 800 °C and beyond; this is the material to prefer when the engine is pushed far from its factory tune.

The +1 mm oversize leaves both stem and length alone: only the head grows, from 30.5 to 31.5 mm. Exhaust gases clear out faster, the cylinder takes in fresh mixture more easily and power goes up. The 12 exhaust seats in the head are then recut to this diameter.

Exhaust valve technical specifications

F1853P is standard size; F1854P and MEVI-1012 are +1 mm. FERREA valves have a 6.55 mm stem, the SUPERTECH valve 6.54 mm.

Valve fitting

When refitting, check that the original MD016483 collets or their replacements match the groove of the chosen valve.

With a 30.5 mm head the exhaust seats stay at their factory size; with 31.5 mm the workshop machines the 12 seats.

The 6G72 valvetrain uses rocker arms with hydraulic lash adjusters: there is no valve clearance to set after fitting.

Technical guide

Our brands

	SUPERTECH, which started out in Silicon Valley, has devoted more than thirty years of know-how to racing valvetrains: valves, springs, guides, titanium retainers. Each valve, whether stainless, titanium or Inconel, is born for one particular engine and refined with rally, track and drag racing tuners.
	FERREA Racing Components came into being in 1978, set up by Horacio Ferrea alongside Daniel Urrutia. Its two factories, in Florida and Argentina, shape stainless, nickel superalloys and titanium for engine builders of every background, from drag racing to NASCAR.

How to choose

Two criteria separate these valves: the head size, which tells you whether the cylinder head seats need recutting, then the material, chosen according to how much boost the engine runs and what the car will be used for.

When reinforced valves become necessary

• Increased boost pressure or larger turbos (Super Alloy or Inconel version advised)
• Firmer springs or sharper cam profiles
• Higher rev limit
• Cylinder head rebuilt for track, drag or rally use
• Factory exhaust valves burnt, distorted or pitted

Vehicle compatibility

OEM part number (exhaust valve): MD183730 (6G72-T) ; MD135480 (6G72)

Don't forget the inlet valves

Before refitting a 6G72 cylinder head, use its time in the workshop to refresh the inlet side too, with new valves and valve stem seals. Inlet valve page: