New York show: Turbo GM V6 out-punches HSV V8

GENERAL MOTORS has developed a new 3.6-litre twin-turbo V6 engine that gives an HSV V8 a run for its money.

The force-fed powerplant is related to the Melbourne-made V6 used in Australia’s home-grown Holden Commodore SV6 but there are no current plans to build the new engine here or slot it into a VF.

However there is faint hope as Holden external communications director Craig Cheetham told GoAuto he “would never say never ... these things are always flexible within GM”.

Churning out 313kW of power at 5500rpm and 583Nm of torque between 3500 and 4500rpm, a substantial 43kW and 53Nm up on the 6.0-litre V8 used in a manual Commodore SS.

It also out-torques the 325kw/550Nm 6.2-litre V8 of an HSV, easily making up for the 12kW power shortfall.

In fact it is the most powerful V6 in GM history and, debuting in the Cadillac CTS luxury sedan at the New York motor show next week, it has the highest specific output in its class at 88kW per litre, compared with the BMW 535i (74kW/L) and 550i (68kW/L).

The power, torque and addition of an eight-speed automatic transmission means the twin-turbo V6-equipped CTS sedan can crack 0-60mph (97km/h) in an estimated 4.6 seconds on the way to a 274km/h top whack.

For comparison, an HSV Clubsport R8 does the 0-100km/h sprint in 5.3 seconds according to test figures by Wheels.

No fuel consumption figures have been announced but it stands to reason that the twin-turbo CTS will consume significantly less premium unleaded than an HSV Clubsport R8 (13.5 litres per 100km) or Commodore SS (12.2L/100km).

Compared with the naturally aspirated 3.6-litre V6 used widely across the GM empire, the twin-turbo unit has received comprehensive modifications including new cylinder head castings, stronger con-rods and machined aluminium pistons.

Helping make the most of the 12psi of boost coming from the two small turbochargers is a compression ratio reduced from 11.5:1 to 10.2:1, a new direct fuel injection system and unique charge-cooling system claimed to all but eliminate turbo lag.

Assistant chief engineer for the twin-turbo V6 engine, Richard Bartlett, explained that the new charge-cooler has “a very short path from the turbos to the throttle body”.

“The compressors draw their air directly from the inlet box and send their pressurised air through the intercooler basically immediately, giving the new CTS a tremendous feeling of power on demand.”

He said the ‘twin-brick’ intercooler configuration is similar to those from the supercharged 6.2-litre LSA engine used in the CTS-V, Chevrolet Camaro ZL1 and is tipped to appear under the bonnet of future HSVs.

“The LSA engine showed us the efficiencies of mounting the intercooler on top of the engine, especially when it came to packaging and maintaining a short, unobstructed path for the air charge,” said MrBartlett.

“It’s efficient and effective – and we wanted to build on that experience.”

The boost pressure of each turbocharger is independently managed using unique vacuum-actuated wastegates and electronic vacuum-actuated recirculation valves, which combine to deliver more low-end torque for smoother, more consistent performance.

Careful monitoring and management of intake charge is achieved via dual mass air flow sensors, an inlet air temperature and humidity sensor, dual turbo inlet pressure sensors and dual manifold pressure sensors.

Mr Bartlett said the new cylinder heads – which have integrated exhaust manifolds plus upper and lower water jackets for thermal efficiency – were designed using computer modelling to optimise port flow, injector spray angle and pattern.

They also have a high tumble intake port design to increase burn efficiency, helped by dished pistons that direct the spray from the injectors around the combustion chamber.

A unique cylinder block casting includes take-offs for turbocharger coolant and oil connections plus higher strength iron main bearing caps.

The block also has positive pressure crankcase ventilation passages for air being forced into the engine by the turbos, rather than sucked into the engine by the downward stroke of the pistons as in a naturally aspirated engine.

Aluminium cam covers are said to improve engine quietness and like the block, are designed to cope with positive crankcase ventilation.

The next car confirmed to receive the force-fed V6 is the Cadillac XTS large luxury sedan.

Cadillac’s last foray into turbocharged V6 engines involved 2.8-litre LP9 engines imported to Mexico from Holden’s engine plant at Fishermans Bend in Melbourne, but ended in 2011 when it ditched turbo versions of the SRX mid-size SUV due to slow sales.