7.5:1, this helped better accommodate the KK&K K-26 turbocharger without inducing pre-ignition. Platinum tipped spark plugs were also used and exhaust valve diameter was increased over the n/a engine. With of boost, output increased to at 5,500 rpm and of torque at 3,500 rpm. The 924 Turbo's engine assembly weighed about more, so front spring rates and anti-roll bars were revised. Weight distribution was now 49/51 compared to the original 924 figure of 48/52 front to rear. In order to aid cooling, as well as to distinguish it from the standard 924, Porsche added a NACA duct in the hood, this helped heat escape when stationary and caused hot air to be drawn out of the engine compartment due to low pressure induced by the louvred alloy engine under-tray when on the move. In addition to the NACA duct, four slotted air vents were installed in the badge panel, with open ducts added to either side the front valance so to aid cooling of the front brakes. 15-inch spoke-style alloy wheels, four-wheel disc brakes with five-stud hubs and a five-speed racing pattern 'dog-leg' transmission was fitted as standard. Power was transferred from the clutch plate to the gearbox through a larger diameter torque tube. Forged 16-inch flat wheels of the style used on the 928 were optional, but fitment specification was that of the 911 which the 924 shared wheel offsets with. A rubber duck-tail spoiler was fitted to the rear hatch, reducing the already low drag coefficient from .36 to .33. Internally, Porsche called the 924 Turbo the "931", much like the 911 Carrera Turbo which had been known as "Type 930". Although right hand drive specific parts were denoted by the prefix "932" both left hand drive and right hand drive cars are referred to as "931", this designation remains in common use by Porsche enthusiasts today. The turbocharged VW EA831 engine allowed the 924's performance to match that of the bigger, more powerful Porsche 928 and come surprisingly close to that of the 911 SC (), thanks in part to a lighter curb weight, but it also brought reliability problems as was often seen in other turbocharged cars of the era. This was mostly due to the fact that the general public did not know how to operate or care for such an early oil cooled turbo setup. Allowing the engine to idle and turbo to cool