A key feature of the Flatnose and Package cars was the M64/50S engine – a key component of the X88 ‘Sport Tuning’ option – a factory derivative of the 1993 IMSA 3.6 Turbo engine built by Andial for Brumos racing. According to the factory, 155 of the M64/50S engines were built. 93 of these engines went into the ‘Turbo S’ cars, 51 engines were installed in standard 3.6 turbo models as special order option ‘X88’ and 11 engines are unaccounted for possibly test engines, sold to dealers as retrofits or sold to customers for race applications.
The ‘S’ designation is denoted by an understated punch stamp!
So just how powerful is this engine? Largely generated from the April 1994 Excellence article early speculation turned to myth that the car was really producing 480 to as much as 508 HP. Speculation was that Porsche had understated the actual figures. Porsche always discloses its horsepower and torque figures from the engine bench. Using this method the ‘S’ engine was rated at 385 HP by the factory in its technical bulletins. Interestingly, most USA MSRP stickers misquoted the rating at 380 HP and some of the earliest USA MSRP stickers misquoted the rating at 355 HP (which was the HP rating for the standard 1994 3.6 Turbo).
The following chart is a non-SAE adjusted rear wheel HP dyno run of a stock X88 engine . The stock engine produced 305 HP to the rear wheels. Depending upon what percentage loss figure you use from crank to wheels the stock unit most-likely produces no more than the factory stated 385 HP at the crank.
The M64/50S engine obtained its increased power from specially modified cylinder heads with different than standard inlet and exhaust ports, upgraded camshafts, modified timing gearwheel and the K27 7006 turbo charger (the K27 7006 has a larger hot side than the K27 7200 in the standard 3.6 Turbo which makes for a 300 rpm later boost onset which lowers back pressure in the exhaust manifold increasing efficiency to make more HP – 7006: inducer/cold 58.5mm exducer/hot 64mm – 7200: inducer/cold 55mm exducer/hot 59mm). Valve timing was advanced from standard for more overlap and richer mixture. Maximum boost pressure was 0.79 to 0.85 bar the same as the standard 3.6 turbo engine (although the onboard computerized boost gauge only reads to 0.7 bar as described in factory technical bulletin ‘9032-9307’).
The following information on the 911 3.6 Litre – Engine with Increased Output – X88 is from the factory technical bulletin ‘Xe’.
Engine with increased output – X 88
Engine – X88 Type – M 64/50S
Scope of Modifcations to M64/50 Engine
Cylinder head intake & exhaust ports modified
Inlet manifold & spacer flanges modified
Valve timing 1.26 + 0.1 mm (inlet valve stroke in overlapping TDC)