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1987 Porsche 928 S4 Twin Turbo

The pinnacle of Porsche 928S4 twin turbo development.  This vehicle was built for one of our customers on the east coast.  The base vehicle is a 1987 Porsche 928S4 with 5-speed transmission and limited slip differential.  This low-mile example still had the fresh leather smell in the interior when it arrived in the fall of 2009.  The twin turbo system (based on our standard 928S4 twin turbo system) included:

  • Twin Garrett GT3071R turbos
  • Twin high-flow ceramic coated exhaust manifolds
  • Twin side mounted intercoolers
  • JDS Porsche Super-MAF with compressed maps
  • 60 lb./hr Siemens fuel injectors
  • Dual 3" stainless steel exhaust with V-band system and Random Technologies race catalysts
  • Upgraded fuel delivery system including dual fuel rail damper system
  • Garrett turbocharger speed sensor, glovebox mounted
  • Turbosmart E-Boost 2 programmable boost controller

The results on this build speak volumes about the performance potential from our work on the 5 liter, 32 Valve Porsche platform.  This car was able to manage a wheel output (on 93 octane pump gasoline) of over 650 HP at below 7,000 RPM on less than 17 psig of manifold pressure.  On 14 psig of manifold pressure, the engine managed to put down 575 wheel HP and 615 ft-lbs of torque.  These results were acheived without any internal modifications whatsoever.  The engine was left totally stock.  These results represent the highest power output acheived on a totally stock Porsche 928 S4 engine running 93 octane pump fuel.  Stock: pistons, rods, crankshaft, heads, camshafts, valves, intake manifold, engine management...but we did change the clutch ;)

The car drives and rides just like any stock Porsche 928S4 until you stick your foot into the throttle.  Then it's a real lesson in "hang on and steer".  This is not a car you let your 17 year old drive, nor the valet at your local restaurant for that matter.  Boost builds quickly, but at a level which is easy to modulate thanks to the 90 trim turbine wheels in the T28 framed GT3071R turbos.  The engine comes alive by 3,500 RPM with gobs of mid-range torque and power and pulls STRONG all the way to 6,500 rpm.

Completed over the summer of 2010, the vehicle was tuned in on the streets and dynamometer and then promptly driven non-stop 900+ miles to the east coast by the owner (with a 24 pack of Red-Bull for support).  Mileage acheived was 20-22 MPG, just like any stock Porsche 928S4 running LH 2.3 and EZK engine management.

We'd like to thank our customer for allowing us to build this fine example of the Porsche 928 and we wish him many miles and years of happy motoring.

© 2011 Kuhn Performance Technologies.