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Z7U —
the 2.5 turbo

The Z7U is the turbocharged 2,458 cc version of the PRV V6 — the very first turbo PRV, launched by the Renault 25 V6 Turbo in 1985, and the engine of the Alpine GTA and Venturi 200.

2 458
CM³
180–210
BHP (PRODUCTION)
1985
FIRST TURBO PRV
Second generation

The engine that changed the PRV's reputation

In 1985, the Renault 25 V6 Turbo introduced the Z7U — and with it the second generation of the PRV V6: offset crankpins for even firing at last, electronic injection, and turbocharging. A far cry from the first-generation units and their uneven beat.

The “magic turbo” quickly reached the flagship versions of several marques — Alpine and Venturi first — making the 2.5 turbo the sporting heart of the PRV family. The full story is told in our History section.

Z7U
DOUVRIN CODE · 2,458 CC · TURBO · 12 VALVES
2458
CM³
Turbo
SINGLE
12
VALVES
The Z7U 700 PRV V6 in the engine bay of a Renault 25 Baccara V6 Turbo: intake plenum marked « Turbo », turbocharger under its heat shield and air filter boxPHOTO TO COME

The Z7U 700 in a Renault 25 Baccara V6 Turbo: the intake plenum carries the word « Turbo »; above it, the turbocharger under its heat shield; on the right, the air filter box, and the red HT leads running across the bay.

Identity

What makes a Z7U a Z7U

Figures read in the constructor's documents held in our Library — the élan 77 technical bulletin, the Z-engines workshop manual and the Pub et Trade data sheets. Nothing here comes from a web fact sheet.

Z7U 2,458 cc · turbo · 12 valves · second generation élan 77 →
91 × 63
Bore × stroke: 91 × 63 mm, 2,458 cc. The stroke is cut from 73 to 63 mm compared with the naturally-aspirated Z6W — that is what turns the 2.8 into a 2.5.
Manetons
Forged-steel crankshaft with offset crankpins, for equal firing intervals at last; new connecting rods, floating-pin pistons, cylinder heads with a stiffened deck and bronze valve guides. Firing order 1-6-3-5-2-4, like every PRV.
Culasse
1.70 mm head gasket. Torque: 6 daN.m in the prescribed order, a three-minute wait, loosen bolt by bolt, then 2 daN.m and a 127° angle tightening — 106° on the Z7U 734.
Garrett T3
Garrett T3 turbocharger with a boost-limiting valve. On the 205 bhp R25 V6 Turbo: 320 ± 30 mbar then 480 ± 30 mbar at the two linkage check points, 1,870 mbar in the manifold at full load, and a safety switch that cuts at 1,300 mbar. On the Alpine GTA V6 Turbo the switch acts between 1.10 and 1.20 bar: same function, two thresholds.
Ralenti
On the catalysed Z7U 700 the idle is not adjustable: 750 ± 50 rpm, checked with the engine warm between 80 and 100 °C, CO below 0.5 %.
Known variants

From 180 to 210 bhp

Six factory or network-approved variants of the Z7U are documented — the full engine-code table is on the main Engines page.

Z7U 700205 bhp
TurboFenix 3B injectionCatalysed
Renault 25 V6 Turbo — the rare case of an engine that GAINED power when catalysed, thanks to a full re-tune.
Z7U 702182 bhp
TurboBendix injection
Renault 25 V6 Turbo
Z7U 730200 bhp
Turbo
Alpine GTA V6 Turbo · Venturi 200
Z7U 732180 bhp
TurboUS market
Alpine GTA V6 Turbo (US)
Z7U 734185 bhp
TurboCatalysed
Alpine GTA Le Mans (catalysed)
Z7U 734 · Danielson210 bhp
TurboHomologated kit
Alpine GTA Le Mans with the Danielson kit — approved by the French authorities and sold through the Renault network.
On the road

The cars of the Z7U

Renault 25 V6 Turbo (1985) →

The launch car — first turbocharged PRV, 182 then 205 bhp. Its stretched Heuliez limousine, in the 182 bhp 2.5 turbo, served president François Mitterrand.

Alpine GTA V6 Turbo → · GTA Le Mans →

200 bhp uncatalysed, 185 bhp catalysed — and back up to 210 bhp with the network-approved Danielson kit, detailed in our Tuners section.

Venturi 200 →

The French hand-built sports car took the 200 bhp Z7U as its entry engine — all Venturi's PRV cars are in the Vehicles section.

And beyond the catalogue

In the late 1980s the independent tuner HAS pushed the Renault 25's Z7U to around 240 bhp — roughly ten cars, one of the great confidential PRVs.

In the Journal

“Renault 25 V6 Turbo — the car of the PRV's second generation” · “the R25's AMG” — the Turbo (M6) TV report on the HAS preparation

In the workshop

What the documents say about the Z7U

Four answers taken from our FAQ, each one read in the Library. The full FAQ holds several hundred more, engine code by engine code.

Z7U, in the documents The full FAQ →
Z7U vs Z6W
What did the Z7U-730 change compared with the Z6W?
Far more than a turbo. élan 77's list: a forged steel crankshaft with split crankpins whose stroke drops from 73 to 63 mm; new connecting rods, made necessary by the larger crankpin diameter; new pistons with floating gudgeon pins; heads with a stiffened deck and bronze valve guides; valves with metallurgy suited to forced induction; a reinforced head gasket; forced induction by a Garrett T3 sitting at the rear of the V, with an air-to-air intercooler and a compressor bypass valve; and Rénix electronic injection with coupled ignition, idle regulation, overrun cut-off, knock detection and rev-limiter cut. élan no. 77, February 1985, page 4. Library →
élan 77
What are the Z6W-A700 and Z7U-730 worth, on the manufacturer's own figures?
élan 77's table sets them side by side. Z6W-A700: 91 × 73 mm, 2849 cm³, compression ratio 9.5:1, 116 kW ISO — 160 hp DIN at 5750 rpm, torque 221 Nm ISO — 23 m-kg DIN at 3500 rpm, two Solex carburettors (a single-barrel 34 TBIA and a twin-barrel 35 CEEI), breakerless transistorised ignition. Z7U-730: 91 × 63 mm, 2458 cm³, compression ratio 8.6:1, 147 kW ISO — 200 hp DIN at 5750 rpm, torque 285 Nm ISO — 29.6 m-kg DIN at 2500 rpm, electronic injection, fully electronic ignition with knock sensor. Common to both: 97/99 super, all light alloy, removable wet liners, hemispherical chamber, 4 main bearings, one overhead camshaft per bank driven by its own simplex chain, valves in a V operated by rockers, firing order 1-6-3-5-2-4, 88 °C thermostat, two 290 mm 120 W electric fans. élan no. 77, February 1985, page 4. Library →
Allumage
Why does the Z7U-730 fire evenly, unlike earlier PRVs?
Because its architecture was reworked for the sole purpose of equalising the firing intervals between cylinders, with an all-new forged steel crankshaft with split (offset) crankpins. The proof is in the valve timing table: the Z6W-A700 keeps two different laws depending on the bank — right 12° / 45° / 50° / 6°, left 10° / 47° / 52° / 5° — while the Z7U-730 shows 8° / 40° / 40° / 8° on both sides. Offsetting the crankpins erased the asymmetry the 90° V6 had carried since 1976. élan no. 77, February 1985, pages 3 and 4. Library →
Culasse
How is a PRV V6 cylinder head tightened?
Threads and bolt-head undersides oiled with engine oil, bolt holes emptied with a syringe. In the prescribed order: 6 daN.m. Wait 3 minutes, slacken one bolt at a time, then 2 daN.m and an angular tightening — 127° on Z7U (except 734) and Z7W 702, 106° on Z7U 734. Then set the valve clearances, run the engine until the fans cut in, let it cool for at least 6 hours, and finish with a further angular tightening without slackening first: 25° in the first case, 45° in the second. After that, no re-tightening at all. Z engines manual, folios 10-23 and 10-24.

Workshop data sheets in the Library

The period Pub et Trade professional data sheets, searchable page by page — sensor resistances, fuel and boost pressures, ignition, cylinder-head torque, valve clearances:

The rest of the family

Architecture, generations and every known engine code of the PRV V6 — on the main Engines page.

Z7X — the 3.0 turbo → All PRV engines →