General Comments

Overall, 3.6 engines are quite reliable and make good power. All the engines are capable of close to 300 HP with decent exhaust, a good tune and a good air filter assembly.

Known Issues

3.6  air-cooled engines come in the following flavors:

1989-1994 964 engines (C2/C4) are essentially the same with the following important exceptions

  • 1989-1991 early 964 engines have an aluminum intake manifold and did not originally use head gaskets.  SOME of these engines had problems with minor leaking from the cylinders and were warranted by Porsche.  This is not a big issue, but now with these motors a 25+ years old the ones which have not been updated are leaking badly.  The repair is at least $10,000 and requires replacement cylinders and machining of the heads.  Although the later engines are more desirable, we do the upgrade to late style head gaskets and replace the cylinders.  The late intake manifold flows a bit  better die to a singel larger thottle plate and the late plastic intake is lighter but this should not be a deal-breaker.
  • 1991 late-1994 964 engines Later engines have a head gasket sealing ring, plastic intake manifolds and a revised throttle body but are otherwise the same as 1989-1991. the change in head gasket style occurred in late 1991 sometime after the change to plastic intake manifolds and the updated throttle bodies.
  • Click here for explanation of the early head leakage issue
  • Performance Upgrades
    • The stock 964 exhaust severely restricts performance and is difficult to fit into a conversion and should be replaced.
    • Upgrading to 993 exhaust with a free flow muffler will add 20 HP, a true equal length system even more, but that has to be purchased separately and adapted.
    • Mass flow units: Lots of shops recommend upgrade the old style – barn door air flow meter to the hot-film mass flow found on the 993.   This is fairly expensive and requires a change in chip tune.   While this makes some sense, because the vacuum from the intake is required to open the air-flow meter causes a minor restriction and could lead to a reduction in throttle response.  In reality this makes almost no difference, maybe 2 HP, and isn’t even measurable on a dyno, when similar tunes are compared.
    • There are gains to be found by using an well designed air filter and cold-air duct.  Beware of the cheap cone filters on eBay,  we offer one style only and it works.  It has a gentle and efficient transition from the filter to the rectangular filter entrance and puts the filter under the decklid grille for access to fresh cold air.


1995 993 engines are similar to the late 964 engines, but have:

  • Engine Type M64-05/06/07/08
  • US Motors have  Secondary air injection
  • Larger intake ports, stacks and manifold runners (43 is 41.5mm)
  • Same diameter intake valves as 964 (49mm)
  • larger exhaust valves (42.5 vs 41.5mm),
  • Smaller diameter valve stems (8mm vs 9mm) for better flow but with a much higher valve guide wear rate
  • hydraulic lifters (which should be converted to solid lifters for racing applications)
  • lighter crankshaft and pulley assembly
  • much improved and revised true dual exhaust system
  • mass flow sensor from the factory
  • more advanced engine management with true sequential fuel injection.
  • Factory power rating is significantly up from the 964 engines but most of this is attributable to the exhaust system.
    • Chips are available for these engines.
    • Contrary to popular belief the Mass Flow sensor makes very little, if any, difference on these motors over the 964 motors.
    • Back to back dyno tests show a difference of 2-3HP gain between same motors.
  • VarioRAM upgrades are available for these engines, bringing the torque up 20% in the 3000-5000 RPM Ranges.
    • VarioRAM Intake Swap
    • Minor electrical wiring change
    • Programming Change

1996-1998 993 US VarioRAM Engines:

  • The most notable change in these engines come from a revised intake which boosts torque 20% from 3000-5000 RPMs.  Click Here for VarioRAM Explained
  • Engine Type M64-23/24
  • Secondary air injection
  • Electronics
    • These engines have ODB-II style DMEs and must be flash re-programmed.
    • 1996 DMEs are not reprogrammable unless a memory chip socket is soldered into the DME
    • This service is relatively expensive ($875) but we can now perform that in house.
    • Our preference is to either use 1996-98 European electronics (as below) but this has become prohibitively expensive since the DMEs are difficult to find and the harnesses have gone from $450 list to $1950 list!
  • All Attributes of 95 993 Engines but:
    • ODB-II DME which must have drive block (Alarm disable) removed to run.
    • Larger 50 mm Intake / 43.5 mm exhaust valves
    • 4 Oxygen Sensors

1996-1998 993 EUROPEAN VarioRAM Engines:

  • These engines are nearly identical to the US engines but they do not have the OBD-II style motronic.
  • No secondary air injection
  • Engine Type M64-21/22
  • They are easily identifiable since they have:
    • 55-pin DME connectors, most boxes are 993.xx.418.011
    • One Oxygen Sensor.
    • The alarm system is integral with the computer system, if fitted.
  • Cyntex aftermarket chips are available for these units.

1996-1998 Euro RS 3.8 Engines

  • See The Truth about 3.8s for a detailed discussion
  • Good luck finding one of these.  Very few were made.
  • For about $11,500 in 1996 money you could buy an upgrade kit with the following
    • RS heads, larger intake valves (53mm /43.5mm) with much larger ports (46 vs 43mm)
    • Magnesium Varioram runners with 46 vs 43mm inner diameter
    • RS hydraulic cams
    • 55-pin DME with appropriate chip
    • 102mm pistons and cylinders (slip fit or bore in could be ordered)
  • These were officially rated at 300 HP, 18 more than the stock varioram.  In reality they made a lot more. That’s a lot of trouble to go to for 6% power increase.

End Note:

VarioRAMs: THESE ENGINES ARE INCREDIBLE!  I recommended against them until I put on in my 1972 targa.  They pull down low like an American V8 and only the European 96-98 engines have larger intake and exhaust valves that all the other motors.  If you can afford it, go for it!