The Porsche 993 flat six engine – the last air cooled boxer

Porsche 993 fährt auf einer Straße.

To this day, the engine of the Porsche 993 is something very special. As the last air-cooled engine in the legendary nine-eleven, this unit is also the most mature of the entire model series.

And even more remarkable, Ferry Porsche died on the very day that the last engine for the 993 was built in Stuttgart Zuffenhausen. Thus, March 27, 1998 became a day that went down in the history of the Porsche company in more ways than one.

Two Porsche 993
© Porsche Archiv

A proven starting point

The engine basis of the 993 is that of its predecessor, the 964. The displacement (3600 cm3) was not changed, but the 3.6-liter engine was thoroughly revised and given the designation M64/05. A more torsionally rigid eight-bearing crankshaft, lightened connecting rods, lighter and further optimized pistons, extended intake ports, lighter and larger valves and rocker arms with hydraulic valve lash adjustment made up the mechanical changes.

For the first time, manual adjustment of valve lash was no longer necessary. This was an important event because the quite intensive inspection costs of the predecessor 964 were from then on a thing of the past.

Porsche 993 engine

In the new 993 engine, the camshafts were also modified and the timing recalibrated. The engine’s cylinders were made of die-cast aluminum, and the running surfaces were made of nickel-silicon. The Bosch Motronic (2.10) was fitted with a hot-film air mass meter.

The base engine initially with 272 hp.

The new engine had the same compression ratio as its predecessor (11.3:1), but was tuned to run on unleaded Super-Plus with 98 octane. At the launch of the 993 model series in the fall of 1993, the engine produced 272 hp (200 kW) at 6100 rpm in the rear-wheel-drive Carrera, 22 hp more than its predecessor. The maximum torque increased to 330 Nm (+20 Nm compared to 964) at 5000 rpm. Because the car also had a slightly shorter gear ratio, the 993 also offered better performance than the 964.

The base of the porsche 993
© Porsche Archiv

As early as the 1994 and 1995 model years, Porsche-Exclusiv offered a power upgrade for the new 911 Carrera to 285 hp (210 kW) at 6000 rpm. This performance upgrade was given the additional equipment code X51. The maximum torque of 350 Nm was reached at 5000 rpm. The additional power was primarily achieved by increasing the displacement to 3.8 liters.

With Varioram 285 hp

Since Porsche customers can never have enough power, the naturally aspirated 3.6-liter engines of the 993 received a power boost to 285 hp (210 kW) starting with the 1996 model year. The engine was thoroughly revised once again and received the Varioram intake system familiar from the Carrera RS.

VarioRam varied the effective length of the intake manifold depending on engine load and engine speed.

Varioram-Ansaugsystem of the Porsche 993
© Porsche Archiv

It was based on the proven two-stage resonance tube system of the 911 Carrera. Varioram supplemented this with the variable length of the intake manifolds and a modified intake manifold volume. At low engine speeds, the intake length was increased, while at higher engine speeds it was reduced. The result was a flatter torque curve, with more torque in the low and medium speed ranges compared to a similar engine without VarioRam.

In this very last engine version of the 993, the hydraulic valve lash adjustment element was also improved; it came from the 911 Turbo.

The intake and exhaust ports in the cylinder head were widened and the valves increased in diameter by one millimeter. The diameter of the intake valve was now 50 millimeters, the exhaust valve 43.5 millimeters. The piston and camshaft contour were adapted.

The Varioram system improved the torque curve in the lower and medium engine speed ranges. Maximum torque of 340 Nm was achieved at 5250 rpm. Engine output increased to 285 hp (210 kW) at 6100 rpm.

Engine of the Porsche 993 with VarioRam
Engine of the Porsche 993 with VarioRam

With this 285 hp, the last air-cooled engine could have gone down in history had it not been for another power stage.

By increasing the displacement to 3.8 liters, both engine output to 300 hp and torque to 555 Nm at 5400 rpm were increased. The price for the X51 option was 12,850 DM in 1996. Of course, these 3.8-liter Carreras are special rarities.

To be fair, though, it’s worth mentioning that the 15 hp difference in performance doesn’t carry too much weight. And even a good-running 993 engine with 272 hp without Varioram provides incomparable driving pleasure.

And no Porsche engine since then has sounded as good as the last air-cooled six-cylinder boxer.

LIMITED EDITION „Porsche 993 – 25 YEARS 1994–2019“ Book

To celebrate the Porsche 993’s twenty fifth anniversary Berlin Motor Books published PORSCHE 993 “25 YEARS” 1994–2019 in a limited edition of 1998 copies.

Special features in this book

  • Detailed purchasing advice and price trends
  • Extensive information about special models
  • Unpublished photographs from the historic Porsche archive
To the book