With 3.4 liters, an 8.5:1 compression ratio, and a pair of modified 993 turbochargers to cope with, the 993 Turbo exhaust headers were the right size to get the spent gases out efficiently. These were duly bolted on and matched to an Axiom Motorsports custom tubing and heavy-duty top-mounted intercooler system.
Finally, and taking into account the limited space between the bodywork and engine, a custom polished stainless double muffler was fabricated to work with the twin-turbo installation.
On the dyno the motor showed a healthy 545 bhp, with 430 lb-ft of torque. These modern levels of 911 Turbo power in the relatively light ’89 car translates into the kind of speeds that are wide-eyed scary when you are peering through, or even over, the short Speedster windscreen.
The stock G50/50 transmission with limited slip differential is one of the most robust boxes in Porsche’s arsenal, so all that was needed here was a general freshening up to cope with the additional horses.
Up front an over-sized center-mount-ed oil cooler was installed, running in series with the stock fender oil cooler. Due to the twin-turbo installation taking up most of the space in the right rear wheelwell area, a 964 Carrera oil tank was placed in front of the rear wheel on that side.
The suspension mods consist of 22mm torsion bars in front and Bilstein RSR coilovers at the rear, with damper valving calibrated to the torsion bars and 400-lb rear springs. Fine-tuning is done by Tarett Engineering’s adjustable front and rear anti-roll bars.
A huge array of wheels is available for 911s these days, but Bobby’s choice of footwear was governed by diameter, width and offset, as well as the correct period look. In the end, Forgeline’s 9.0J- and 11.0Jx19-in. three-piece forged alloy wheels, shod with Michelin Sport rubber, 235/35ZR19 and 295/30ZR19, came out tops. Apart from meeting all of the above criteria, they also help to reduce unsprung weight.