• The 964 (3.6 1989-1994) makes almost as much power as a 993 but has inferior electronics, primarily the old (1980s) vintage “barn door” air flow meter.  It has solid lifters (i.e. need adjustment)  and the factory exhaust is garbage which accounts for the 25 less (247 vs 272) rated HP.
  • With the same exhaust, there is maybe 5 HP difference, between a 964 and 95 993, if that.
  • 964 engines have rust issues with the sheet metal and in head studs.  The 993 sheet metal does not rust.  It is very thin and most likely stainless or coated.
  • Head Studs
    • The 964 used either lower steel and upper dilivar and or all dilivar.  All 964 studs supersede to 993 studs.
    • The 993 studs are dilivar and I have not seen failures.
    • 993 RS studs are fully threaded and similar to GT3 but a different length, these are VERY expensive (like 2.5x steel price)
    • Note that 3.2 and earlier had upper steel and lower dilivar studs that were prone to failure.  I have no great explaination for this however note that neither 964 or 993 studs are exposed to airflow, the find in the cylinders to not go through to the clearance holes.
  • ValveGear and such
    • The 993 non-vram is a nice motor.  It has hydraulic lifters, plastic valve covers, and a hot-film mass-air flow meter which means better electronics.
    • The 964’s solid rockers make it easier to upgrade cams, on a 993 to do the same upgrade, you use modified 964 rockers, and that will set you back $1500.
    • The ports are slightly larger than 964.  Valves are the same size. (49/42.5)
    • Vram gets 1mm larger intake valve (50) and 1 mm larger exhasut valve (43.5).
    • 993 3.8 RS intake valves are 51.5mm and the same size (43.5mm) as standard 993.
    • All 993 motors have 8mm valve stems, vs 9mm on the 964 and all earlier 911s. This leads to issues with exhaust guides at about 100K miles.  Replacement valve guides are significantly harder bronze phosphorous and I have not seen any replacement issues, then again, you are good for 100K miles.
  • Electronics
    • All 1995 993s have 55 pin DMEs and they can be tuned by swapping a chip.  US Versions used one channel for the emissions blower.
    • All Euro 993s (1994-1998) had the same ECU with the VarioRam (96-98) using one channel for the Vram and a different tune.
    • US 1996-98 Vrams had an 88 pin DME, the 96 version is different and cannot be reprogrammed, the chip is soldered to the motherboard and attempts to replace it end badly.  I know this because I did three and all eventually failed between 6 months and 2 years, at $1200 a pop in 2003 dollars.  FVD offered nothing, not even condolences.
    • All 88 pin DMEs have Driv-Blok and since 96 cannot be reprogrammed they are worthless.  For the 97-98 few can reprogram it to remove the alarm system, and they cannot be tuned easily even if you have a dyno (which I do, at my house!).  You can also attempt to install the 993 chassis harness and alarm box and push the button on the key fob whenever you start the car, I looked this and thought wiring aftermarket ECU would be simpler!
    • It is possible to rewire the 88-pin DME harness to hook to a 95/Euro ECU.  This is not fun but I have done half a dozen.  The 95 and 96-98 euro harnesses are unavailable from the dealer.  I can also rewire the 95 harness to operate the varioram and have chips that make it seamless and identical to the Euro Vram.
  • VarioRAM
    • The 993 Vram engine has 20% more usable torque (HP) from 3000-5000 RPMs.  What that means is that you don’t need to downshift to pass someone.  All are MILES better than a 3.2.  The compression ratio is 11.2:1 vs 9.2:1 and they are twin-plug, larger (by 15% since a 3.2 is not really 3.2) etc.
      • If you add a Vram to a 95 motor you then essentially get a 96-98 euro Vram, minus slightly larger valves, which are good for a few (6=8) HP.
      • The VarioRam itself has no effect on max power.  The larger valves are good for 6-8 HP or so.  I buy every VRam I can find up to $2000 and put them on 95 motors.  How many have I done?  This is maybe half.
      • If you look, at the torque graph you will see that all that torque is due to the intake alone, and both 95 and 96-98 engines make the same on the top end, this was done on the same dyno as I have and is rear wheel and very conservative:
  • Thru Bolt Leakage
    • There is no thru-bolt upgrade, the o-rings should be replaced if the engine is serviced.  This is not fun and requires stripping the engine down to the short block.,  Link Here
  • Cranks, Rods and Rod Bolts
    • The 964 crank is heavy and needs a harmonic balancer. DO NOT REPLACE THE CRANK PULLEY
    • The 993 crank is lighter and more rigid and does not require a harmonic balancer. Despite the pulley having 3 rows, it’s hollow and light.  This is essentially the same crank used on the 996tt motor, which can make 1000 HP, and the GT3 through 2014, which spun to nearly 9000 RPMs and had titanium rods.
    • 964 uses 930 rods, designed in 1977 for the 1978 911 3.3 turbo. They are beefy (heavy) and use 9mm rod bolts versus 10mm on the 3.0. This was necessitated by clearance to the oil pump with the larger (74.4 and 76.4 vs 70.4) stroke.
    • 993 uses a much newer and lighter rod, also forged, with a narrower rod bearing and piston pin bushing. .
    • On 964 engines it’s wise to replace the factory rod bolts with ARP or 993. The stretch bolts are prone to failure.
    • Both 993 and ARP rod bolts are designed to be reusable and are not torqued to yield (google it).
    • 993 factory rod bolts are good bolts.  They supersede to 996, from the 996 twin-turbo but it’s the same design.
    • 993 rod bearings supersede to 996 turbo,
  • All properly rebuilt 964s have replacement cylinders (pistons are the same early and late), new rings and the heads are machined to the late style, they never changed the casting so the result is exactly the same as a 92-94 head but with a fresh surface.  We can also update to the later plastic intake which is lighter and flows better.  Link Here
  • We are happy to build or install anything you want. I price them on a cost-plus-basis so….  I have also built 964s with 993 electronics, but that gets as expensive as a 993…or maybe more.

MYTH: The VarioRam engines are too complicated and the 95 non-VRam motor is better.  Complete BS.

TRUTH: The 88-pin ODB-II DME (thanks California and emissions whackos, since the 96-98 motor is no cleaner!) is a pain to remove the Driv-Blok from and is also hard to tune.

CAVEAT: Replacing the 88-pin DME with a 55-pin (ODB-I) DME is viable as is adding a Vram to a 95 motor.

BS Check: Did I mention I teach UD senior mechanical engineering students engine design and started the Automotive Engineering concentration?