Alfa Romeo 75 Turbo Evoluzione IMSA
Alfa Romeo 75 Turbo Evoluzione IMSA
The Alfa Romeo 75 IMSA, fully known as the Turbo Evoluzione IMSA, was a racing special based on the Alfa 75, built specifically for the prestigious Italian Giro d'Italia Automobilistico and touring car circuit racing in general. Despite its name referencing the North American motorsports federation, the car rarely raced in America. Instead, it took advantage of IMSA's more relaxed legislative rules compared to Group A, allowing Alfa to build a brutally modified racing machine.
The goal of Alfa Romeo's racing department was to enter the under-2.5-liter category, where its main rivals were the BMW M3 (E30) and the Ford Sierra RS Cosworth. Although Alfa Romeo had a V6 engine under 2.5 liters at its disposal, they opted for the 1.8-liter unit from the existing 1.8 Turbo (also sold as the "America" version alongside the 3.0 V6). The reasons were engine weight, front-axle load, and the greater tuning potential of a turbocharged engine compared to a naturally aspirated one. To fit into the 2500 cc category—considering the 1.4 multiplication coefficient for forced induction—the displacement of the standard 1779 cc engine had to be reduced. This was achieved by decreasing the bore while keeping the stroke the same. The bore was set at exactly 80 mm, resulting in a total displacement of 1762 cc.
To homologate the car for competition, regulations required a production run of 500 road-going units. These became rare and expensive items the moment they were released, and they remain so today. This gave birth to the limited series known as the Alfa Romeo 75 Turbo Evoluzione. Its appearance was so distinct that there was no mistaking it in a rearview mirror. The car featured a special body kit with flared arches, side skirts, and unique bumpers—most notably the front one, which looked as if several bumpers had been stacked on top of each other. The sides were dominated by bold black "75 Turbo Evoluzione" decals. Customers didn't have to worry about choosing a color; there was only one... the "right" one: Rosso Alfa (code AR130). The look was completed by 15-inch magnesium wheels from the GTV6, painted in the same shade of red.
I personally see the choice of wheels as the car's greatest aesthetic weakness. On these rims, the car looks like a weightlifter who only trains his upper body. They detract from its presence and look somewhat out of place. Although these wheels are original, most owners quickly swap them for larger ones. Furthermore, the 195-section tire width doesn't exactly help with handling or traction, given the somewhat unpredictable surge of power and torque sent to the rear axle.
I've always wondered why Alfa chose these specific wheels, and I'm certain it wasn't a mistake. There were several pragmatic reasons. First, it was cost-effective to use what was already on the shelf. Larger wheels were rare at the time, and finding suitable performance tires for larger rims would have been problematic. Additionally, larger wheels mean more unsprung mass and greater inertia, which negatively affects handling. There was also a rule in Group A racing stating that a manufacturer could only use wheels up to 2 inches larger than those on the production car. Since Alfa planned to race on 17-inch rims, they started with 15-inch ones for the road car. Despite the plastic body kit, the Turbo Evoluzione still used the standard body shell and wheel arches; larger wheels would have caused clearance issues. Low-profile tires were also uncommon then and would have compromised ride comfort. The aero kit was designed to drop the drag coefficient from 0.38 to 0.33, and it was optimized specifically for 15-inch wheels. Finally, since the brakes were mounted inboard (at the gearbox), there was no technical need for larger rims to clear the calipers. For context, its rival, the BMW M3, also wore 15-inch wheels. It was a pragmatic choice based on multiple factors.
Returning to the Turbo Evoluzione's engine: despite the slight reduction in displacement, its official output was listed as 155 hp—identical to the standard 1.8 Turbo. However, numerous tests and measurements suggested the real output was higher, with some examples reportedly reaching up to 200 hp. These homologation specials reached a top speed of 210 km/h and accelerated from 0 to 100 km/h in 7.7 seconds—impressive figures for their time.
Today, however, we want to focus predominantly on the IMSA (International Motor Sports Association) version. As mentioned, the 1.8-liter engine was the clear choice due to its lower weight over the front axle, higher durability, and, most importantly, the massive tuning potential offered by turbocharging. A naturally aspirated 2.5 V6 would have struggled to even glance at the 400 hp mark. One must also consider the development costs.
The engine itself (internal code 061.54) shared virtually nothing with the base power unit except for the valve cover and basic external appearance. Every internal component was radically re-engineered to withstand enormous boost pressures. By reducing the bore to 1762 cc, the wet liners became thicker and more durable, further enhanced with a Nikasil coating. The aluminum block was reinforced in key areas. Forged pistons from Pankl or CP Carrillo with modified crowns were used, dropping the compression ratio from 8.0:1 to 7.5:1 to prevent detonation under high boost from the Garrett turbocharger (a larger unit than the standard T3). Boost pressure reached a staggering 2.2 bar. These pistons were paired with connecting rods made from Nimonic or high-strength steel, offering significantly higher tensile strength.
The cylinder head underwent extensive modification as well. Valve diameters were increased to 44 mm for intake and 38 mm for exhaust, the latter being sodium-filled for better heat dissipation—a signature Alfa Romeo technique even in their road cars. Valve seats were crafted from beryllium copper for its extreme thermal conductivity. Both intake and exhaust ports were reshaped and polished to optimize gas flow. Camshafts featured a "hotter" profile with higher lift and longer duration to improve cylinder scavenging. Furthermore, the standard head gasket was replaced with individual steel O-rings to seal against the high combustion pressures. To meet the extreme lubrication demands under high G-loads and high RPM, a switch to a dry-sump system was mandatory. This allowed the engine to be mounted lower, dropping the center of gravity, with an external tank and a high-capacity oil pump ensuring constant flow.
The car was equipped with sophisticated electronics to manage fueling and boost. Unlike the standard Bosch L-Jetronic, the IMSA version ran on a fully programmable Marelli-Weber IAW unit—the same system found in the Lancia Delta S4 and the Ferrari F40.
Two injectors per cylinder were used to ensure sufficient fuel delivery at maximum boost and to eliminate the risk of leaning out and melting a piston. Special ignition coils were required to ignite such a rich mixture. The system worked with an array of sensors measuring everything from manifold pressure and throttle position to intake air and exhaust gas temperatures. The intake manifold was redesigned, housing a massive throttle body (up to 70 mm), while fuel was supplied by two high-flow pumps located in the trunk.
While standard road cars used a mechanically regulated wastegate, the IMSA version allowed the driver to control boost directly from the cockpit. Via a rotary dial, the pilot could adjust power on the fly—either to save fuel or to summon maximum grunt for an overtaking maneuver.
A massive intercooler handled the charge air cooling. The exhaust headers were a 4-into-1 design with equal-length runners, leading into a stainless steel system free of mufflers or catalytic converters, exiting just ahead of the rear wheel.
The result? Between 335 and 400 hp depending on the setup. Considering the baseline of the road-going Turbo Evoluzione, this power hike is shocking. It represented the absolute performance ceiling and the true "Evolution" of the legendary bialbero engine.
With a vehicle weight of approximately 960 kg, the performance exceeded all expectations. Top speed depended on the gearing but surpassed 270 km/h, while 0–100 km/h took between 4.5 and 5 seconds.
However, where the car truly reigned supreme was its immense cornering grip. This brings us to the chassis modifications, which were no less radical than those of the engine.
The De Dion rear axle layout was retained but modified to allow for camber adjustments—something the road car lacked. The wide body kit allowed for a significantly wider track and massive racing slicks. The front suspension utilized inverted lower ball joints to shift the roll center and increase negative camber gain under compression. Most rubber bushings were replaced with uniballs (spherical bearings), providing laser-precise handling and eliminating any unwanted play. Interestingly, the front end kept its torsion bar setup but supplemented it with additional coilover springs.
A fundamental change occurred on the rear axle regarding the brake placement. The original inboard brake concept (brakes located at the gearbox) was abandoned, and the brakes were moved to the wheel hubs. Although this meant an increase in unsprung mass, the change allowed for the use of larger discs and more efficient cooling. Furthermore, it prevented heat build-up around the gearbox. The gearbox featured a reinforced shaft and straight-cut gears (innesti frontali), enabling faster shifting and greater durability. The oil system was equipped with its own auxiliary cooler and pump. The single-plate clutch was replaced by a multi-plate design.
The original limited-slip differential, previously set to 25% lock, was tightened, often exceeding 50%. At the same time, the driveshaft was lightened and its durability increased.
The Alfa Romeo 75 Turbo Evoluzione IMSA outclassed all potential rivals between 1988 and 1989. In the Giro d'Italia Automobilistico, which combined road stages and circuit racing, it remained undefeated. In the 1988 season, three IMSA Alfas occupied the top three positions with drivers such as Riccardo Patrese, Miki Biasion, and Tiziano Siviero. That same year, Gianfranco Brancatelli became the Italian Touring Car Champion behind the wheel of this car. The following year, the car defended its triumph, this time with the crews of Giorgio Francia, Dario Cerrato, and Giuseppe Cerri.
Photo: Stellantis Heritage Media / Alfa Romeo