Reinforced exhaust valves Nissan 300ZX Z32 VG30DE VG30DETT

Nissan engines covered

The Z32 generation 300ZX uses Nissan's 3 litre VG30 V6 with 24 valves and twin camshafts per head: naturally aspirated as the VG30DE, or twin turbo as the VG30DETT.

The V6 has 12 exhaust valves, two per cylinder. On the VG30DETT, the original valve has a 29.49 mm head and a 5.946 mm stem; the two turbos send it hotter burnt gases as soon as boost rises.

SUPERTECH and FERREA reinforced exhaust valves

In a VG30, every exhaust valve opens onto a stream of gas fresh from combustion, and nothing in the cylinder head is more exposed to heat. Its head metal swings between 760 and 870 °C on the unboosted VG30DE, and exceeds 1,000 °C on the VG30DETT as soon as its two turbos blow. Nearly 75 % of that heat leaves via the seat, about 20 % via the guide. Yet steel gives way as temperature rises: EV8 grade, used as the reference, withstands 550 MPa at 600 °C, then just 300 MPa at 800 °C. Raising boost, revs or load adds further heat; the head fatigues, distorts and no longer guarantees a seal.

To resist that heat, reinforced valves turn to nickel alloys. SUPERTECH chooses Inconel for its NEVI-1017, a superalloy that keeps 860 MPa at 730 °C and 554 MPa near 815 °C, about 85 % better than EV8 steel around 800 °C, with a chromed stem that slides more easily in the guide: the right pick for a VG30DETT whose boost is being raised. FERREA for its part offers its Competition Plus range in Super Alloy, also nickel-based, for which the maker announces 20 % more strength when hot and seats that last 25 % longer.

Two enlarged heads round off the range: 30 mm from SUPERTECH (+0.5 mm) and 30.5 mm from FERREA (+1 mm). Only that diameter changes; the exhaust purges sooner, the inlet side benefits and the V6 gains power. The 12 seats are then recut to the chosen size.

Exhaust valve technical specifications

F1849P: 29.5 mm head (standard); F1850P: 30.5 mm (+1 mm); 6 mm stem, 103.65 mm length. NEVI-1017: 30 mm head (+0.5 mm), 5.97 mm stem, 103.7 mm length.

Valve fitting

On reassembly, check that the 6 mm collets bear properly in the groove of the new valves; the KPR-6N-6-ST collets suit the VG30.

At 29.5 mm the seats are simply recut; at 30 or 30.5 mm, the 12 exhaust seats of both heads are machined.

Keep the same size and brand on all 12 valves and replace the exhaust valve stem seals, for example with VS-N6E-12.

Technical guide

Our brands

	SUPERTECH, born in California within Silicon Valley, has produced every component of the racing valvetrain for over 30 years, titanium retainers included. Stainless, titanium, Inconel: each part number targets one engine and goes through the test of renowned tuners.
	FERREA Racing Components, founded in 1978 on the initiative of Horacio Ferrea and Daniel Urrutia, runs two sites, one in Florida, the other in Argentina. There it works stainless steel, titanium and nickel superalloys for engine builders of every country, from NASCAR to the drag strip.

How to choose

Gripped under the retainer, the collets anchor the valve by its groove. On this V6, you first choose the head diameter, on which seat machining depends, then the material, on which heat resistance depends.

When reinforced valves become necessary

• Turbo boost raised or bigger turbos (Inconel version recommended)
• Sharper cam profiles, stiffened valve springs
• Cut-out speed pushed back
• Circuit or drag strip use
• Rebuild of both heads with burnt or distorted exhaust valves

Vehicle compatibility

OEM part number (exhaust valve):

Don't forget the inlet valves

With both VG30 cylinder heads off, renew the inlet side simultaneously, with a fresh set of valve stem seals. You will find the inlet parts for this V6 below: