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Engines: 3.6 and 3.8 litres In 1989, Porsche
introduced the 964 series, and the 3.6 litre engine. These engines have
excellent power improvement potential with a few caveats which are discussed
below. Distributor belt breakage The 3.6 was the first
production 911 engine that came equipped with twin-ignition. Porsche used a
unique dual-distributor that was inexpensive to produce, compared to the RSR
unit, that was generally reliable. The only problem was a premature failure
of the rubber belt that drives the second unit caused by ozone gas buildup
inside the distributor. When the belt broke, the second rotor quit turning,
resulting in erroneous timing in the cylinder that the rotor was pointing at
the time of breakage. This usually resulted in serious damage to that piston
and cylinder. Installing the factory vent kit fixed this problem by forcing
pressurized air from the cooling shroud through the distributors to evacuate
the ozone gas that attacked the rubber. Its still prudent to change the
distributor belt every 50K miles as good, proactive maintenance. Rennsport
Systems
offers a belt replacement service for $ 220 that includes the new belt, a
factory vent kit, (if you do not have one) and all labor. Bearings, if needed
are extra. These engines were also
equipped with a knock sensor on each bank of cylinders so that the Motronic
unit could selectively retard a cylinder that was detonating. Although Porsche claims a
compression ratio of 11.3:1, we have measured many of these engines around
10.3 to 10.7:1. The only pistons that came closer to 11.3:1 compression ratio
were the 101.1mm pistons from the 350 HP 3.8 RSR engines. Cylinder Leakage The first generation of
3.6 litre engines were not equipped with head gaskets. The cylinder sealed
directly to the mating surface in the head to contain compression pressures.
These style cylinders were use from 1989 until approximately 1991. The 92
C2/C4 and all 993 cars used an improved cylinder that had a sealing ring type
of head gasket. Some of these early 3.6’s seeped oil at the top of the
barrels and this is something to consider when contemplating an engine
improvement program. Connecting Rod Bolts Porsche utilized smaller,
lighter rods in the 3.6 litre engines for internal clearance and to save
reciprocating weight and they continued using the 9mm rod bolts from the 3.2
Carrera and 3.3 Turbo. When operating these engines above 6800 RPM or for
extended periods of time, we have seen failures of these critical bolts with
catastrophic effects. To that end, we strongly recommend either limiting
maximum RPM to the Factory fuel-cutoff at 6750 RPM or installing stronger rod
bolts such as ARP or Raceware ones.Aftermarket racing rods like Pauter
Engineering or Carillo ones are highly recommended as well. If you install a
performance chip, make sure that the stock rev limit has not been altered
unless the rods and/or bolts are upgraded. Valve Springs Another item that has
surfaced after a few years of racing and watching customers participate in
Driver Education Events is valve float when someone misses a shift. The 3.6
engine use large, heavy valves that put quite a strain on the weak
stock valve springs. After some time, the springs lose some of their tension
that results in valve float occurring at a progressively lower RPM. When this
happens, the valves can no longer close accurately at high RPM and will
strike the piston crowns resulting in bent or broken valves. This sort of
failure can be very expensive. The fix for this problem is to install a set
of good racing valve springs and titanium retainers to lower valve train
weight. All 3.6 or 3.8 litre engines used for track events or racing need to
have this issue addressed. Dual Mass Flywheel Failures The dual-mass flywheels
were most problematic during the 90-92 model years. At the end of the 92
model year, Porsche began installing the LUK brand dual-mass units which were
more durable. Its is recommended that you install the OEM LUK flywheel or the
much lighter one from the 3.8 Carrera RS. This lightweight flywheel really
helps pick the RPM up quicker but does require a different chip in the DME to
prevent stalling. The European-only 3.8 Carrera RS uses a different DME box
than the USA-spec cars. Performance Enhancements There are several things
that can be done to improve engine power although not everything is cost
effective. The 993’s especially, are very efficient engines that are quite
well optimized as they are delivered from Porsche. Changes to these cars will
be expensive and certain changes can make the car trigger "Check
Engine" lights or difficult to pass emission tests. The first thing that we
recommend for all 3.6’s is a performance chip. This optimizes the ignition
timing and fuel curves for more torque and throttle response at the cost of a
narrower detonation margin. You must use 92 or better (pump) octane fuel in a
"chipped" engine to prevent internal damage. This is the single most
cost effective improvement that you can make. The 3.2 engines can benefit
from the installation of a Mass-Airflow Sensor and larger Throttle Body.
These are also quite expensive from a $$-per-HP perspective. SSI Heat
exchangers and a good sport muffler will also help the 3.2. The 89-94 C2/C4 Porsches has a fairly restrictive and heavy exhaust system that has room for improvement. Installing a bypass pipe and removing the final muffler will save some weight and helps the power somewhat. Although they have proven troublesome, the B&B headers and mufflers adds a little power albeit with more noise, especially inside the car. This setup would be for off-road only since the catalytic converter is eliminated. We also strongly recommend removing the tray under the engine in these cars since it seems to accelerate engine wear due to the contained heat. Here are some performance improvements for street driven cars:
Other Modifications The "Cup"
Airbox modification that adds several additional holes to the air cleaner
cover results in more intake noise and little bit more power. The Factory
airbox and throttle body are well matched to the operating range of the stock
engine in most cases.
Here is a 993 3.8 RSR engine that makes 350 HP. This
intake features a dual-plenum intake manifold that has six individual
throttles. This is required for engine operation above 7000 RPM. There are several
camshafts available for the 3.6 litre engines. Unfortunately, most of them
are not street legal and will not pass US emissions tests. For track use
only, there are some sport-type cams that will make more power above 6500 RPM
than the stock components. One of the best ways to
increase performance in the 3.6 litre engine, regardless of model year is to
install the 3.8 litre; 101.1mm piston and cylinder set. This will add torque
uniformly across the RPM range without affecting emissions. There are two
different P/C sets. One is a slip-in thin-wall cylinder that doesn’t require
any case machining and the other is a thick-wall cylinder that must have the
case spigots enlarged. This is a much better part for racing since these
large cylinders tend to distort and lose ring seal when hot. For street
applications, the thin-wall sets are satisfactory. The Factory European
Carrera RS engine kit is also worthwhile considering when its time to rebuild
the engine. This kit includes 3.8 litre P/C set, RS cams, 6 new heads with
bigger valves, single belt pulley, larger intake risers,and a sport exhaust.
These have been dyno'ed in Germany at 300-335 HP. A new chip is necessary for
this conversion.
This 102mm 3.8 billet cylinder that we had made for a
special application used a custom JE piston and has NikasilŪ bores. Notice
the extra metal left at the top of the cylinder to help it seal to the head
and eliminate the distortion that sometimes occurs with the OEM Mahle
cylinder. Since the top of the cylinder operates much hotter than the bottom,
the cylinders are more stable when using very high compression ratios. The 993 version of the
3.6 litre engine featured hydraulic lifters to eliminate valve adjustments
and lower maintenance costs. When these engines are operated at high RPM(over
7000), these lifters are prone to failure and a common modification is to
install the older, solid lifters as used in the 89-94 engines and all
versions of 3.8 RSR. This requires new rocker arms and lifters. Another performance
enhancement is head flow work. While the stock intake ports flow OK for
street use, the exhaust port and its ceramic liner show flow improvements
better than 30% with some handwork. This also eliminates a major
"step" where the liner meets the valve seat. Engine Swaps: 3.2 or 3.6 Litre engines into Pre-89
911's These conversions are
becoming more commonplace as the current crop of 2.2, 2.4, 2.7, 3.0, and 3.2
litre engine are getting tired and installing a modified 3.2 or 3.6 into
these earlier, light cars is a huge leap in performance. A 3.2 Carrera engine
converted to 3.4 litres, twin-ignition, early exhaust and some head & intake
manifold work yields over 250 HP and makes these cars very fast. Its not
difficult to mate the 3.6 litre engine to a 915 and retain all the
drivability of the Motronic powerplant, if this is done properly. Here is an early SC with
a VarioRamŪ 3.6 connected to a close-ratio, LSD-equipped 915 transmission.
This car has Turbo brakes and a full street suspensiion upgrade to make this
car a genuine rocket.
As the owner wished to retain heat and defrost
functionality and the lowest possible noise without restricting power, we
used the excellent 993 Factory heat exchangers and adapted them to his
existing Monty Sport muffler. Two of the four oxygen sensors were needed for
the OBDII-Motronic and a custom chip was made for this car.
For further information about these engines and the
various configurations that are possible for street and track use, contact us
at 503.244.0990 or e-mail to: info@rennsportsystems.com
Since engine modifications are done on an individual custom basis, contact Rennsport Systems for specific recommendations about your application E-mail: info@rennsportsystems.com 503.244.0990
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