06.01.2005 Alfa Romeo Twin Turbo - Alfa’s GM boomerang

Recent rumours emanating from Alfa Romeo’s development centre are being met with widespread acceptance by Alfa Romeo enthusiasts, who are keenly looking forward to the marque’s next generation of sporty cars.

Although it has to be anticipated that several of the projects in the development schedule will not make it into production, optimistic onlookers do however perceive a bright future. The current mentioning of Maserati parts sharing schemes, new large-capacity V8 power units, and all-wheel-drive thoroughbreds, all hammer home the desired direction of Alfa Romeo as a limited-compromise manufacturer of luxury sports cars.

Another, perhaps less-romantic side is the General Motors Powertrain joint venture. With many enthusiasts going green at the thought of characterless Alfa’s, it is worth mentioning that Alfa Romeo have an ironic and highly interesting past with General Motors.

This is a story which also ties in with the future 1.9 M-Jet Twin Turbo engine, a unit expected to debut on the Alfa 148 in 2006. The twin-turbo diesel engine is a result of the GM-Fiat Powertrain joint venture, with the general technology behind the engine already having been presented on the Opel Vectra OPC concept.

Fortunately, the advanced serial turbo charging technology which is to be used on the Alfa Romeo unit dispels the traditional disadvantages associated with bi-turbo systems, and allows for the ‘perfect’ combination of increased performance with lower fuel consumption.

The idea behind the new serial design is quite different from that of conventional parallel twin-turbo systems, with the two turbochargers being used both individually as well as collectively according to conditions.

At low engine speeds, up to 1,800 rpm, air induction is delivered without lag by a small, high spool rate turbocharger that is able to deliver up to 3.2 bars of pressure. The effect is immediate, with a tremendous 400 Nm of torque available from as low as 1,400 rpm on the 1.9 litre Opel prototype engine.

As the revs rise over 1,800 rpm, a butterfly valve, controlling the exhaust gas pressure to a second high volume turbocharger, starts to open.
 

The Callaway C3, built at request of the US importer 'Alfa Romeo Incorporated' and supported by the factory,  was designed to trounce the Maserati Biturbo

The new serial turbocharging system will offer tremendous improvements in both peformance and economy for the Alfa Romeo 1.9 M-Jet Diesel twin-turbo engine


With the rpm needle moving up to the 3k marker, the large turbocharger feeds increasing loads of air into the system, backed up by the additional boost of the small turbo.The exhaust gas butterfly valve opens fully at 3,000 rpm, with the large high volume turbo charger now in full control, dumping the engine with ever increasing amounts of cool air up to the red line.

The result is shockingly aggressive, like a steroid infuse gone berserk. There is no need to rev this engine to it’s limit, however, as the peak torque available between 1,400 and 3,600 rpm is where the acceleration is at its best. The 0-100 km/h dash is reached in a lightening 6.5 seconds.

Astonishingly, the new engine has delivered preliminary fuel consumption figures are lower than those of the current 1.9 litre JTD engine, making this a true masterpiece of engineering excellence.

And the ironic link with the past? Well, the Twin Turbo GM unit transpires in spirit from the 1983 Callaway C3 GTV 6, a car designed to Alfa Romeo’s specifications to trounce the Maserati Biturbo’s Stateside appeal.

The Callaway C3 GTV 6 was a properly developed car, designed to withstand the rigour of Alfa Romeo’s in-house testing programmes. The intercooler packaging was particularly well thought out, replacing the intake plenum on top of the engine to ensure effective cooling whilst reducing turbo-lag issues.

Despite the high costs of the Callaway GTV 6 - over 200 man hours went into each car -, and low production volume, the car was considered as a major success. Indeed, it was the GTV 6 that initiated Callaway’s projects with the Chevrolet Corvette after a GTV 6 ended up impressing General Motors on the proving ground.

The success of the Callaway C4 Corvette Twin Turbo, produced from 1985 to 1991, both on track and as a road-going ballistic missile, has come full circle. Now the essence of twin turbocharging, pursued by General Motors following their interest in an Alfa-based special, is set to blow Alfa Romeo’s future range into a new dimension.
By Paddy & James Granger