The 3.6 litre engines really have excellent power improvement potential with a few caveats which are discussed below.

Known Issues

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. We do offer a distributor rebuilding service to replace the belt and bearings, if needed.

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 11.1:1, we have measured many of these engines and they range from 10.6 to 10.8:1. The only pistons that truly had the 11.3:1 compression ratio were the 102mm pistons from the 3.8 RSR engines.

Cylinder Leakage

The first generation of 3.6 litre engines from ’89 to mid-’91 were not equipped with head gaskets and a few of them leaked a little bit. These cylinders sealed directly to the mating surface in the head to contain compression pressures.  The ‘92 C2/C4 and all 993 cars used an improved cylinder that had a sealing ring type of head gasket. Not all of these early 3.6’s seeped oil at the top of the barrels but this is something to consider when contemplating an engine improvement program. If the cylinders are in excellent condition, we can machine these older 3.6 ones to accept the late sealing rings so replacement isn’t necessary in those situations.

Connecting Rod Bolts

Porsche utilized smaller, lighter rods in the 993 3.6 litre engines to save reciprocating weight and continue the use of the 9mm rod bolts from the 3.2 Carrera. When operating these engines above 6800 RPM or for extended periods of high-RPM operation, we have seen failures of these critical bolts with catastrophic effects. To that end, we strongly recommend either limiting maximum to the Factory fuel-cutoff of 6750 RPM unless stronger ARP rod bolts or aftermarket racing rods like Pauter Engineering or Carillo ones are installed. If you install a performance chip, make sure that the stock rev limit has not been altered.

Valve Springs

Another item that has surfaced after a few years of racing these engines and watching customers participate in Driver Education Events is valve float when a shift is missed. The 3.6 engine uses large, heavy valves that put quite a strain on the 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 perhaps some 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 by using better springs and Titanium retainers.

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. Substantial modifications to these cars can be expensive and some changes can render the car unable to pass emission tests so consult with us on a suite of performance enhancements that will meet your requirements.

Performance Chips

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 should use 92 or better (pump) octane fuel in a “chipped” engine to get maximum performance. Dollar-for-dollar, this is the single most cost effective improvement that you can make. Other things are Mass-Airflow Sensors (964) and larger Throttle Bodies that have dubious results. These are also quite expensive from a $$-per-HP perspective.

Custom Exhaust

The ‘89-‘94 C2/C4 Porsche 964 has a fairly restrictive exhaust exhaust system in stock form that has room for improvement. Installing a bypass pipe and removing the final muffler saves some weight and really helps the power. Although they have proven somewhat troublesome, the B&B headers and mufflers do help add power a bit, albeit with more noise, especially inside the car. We also strongly recommend removing the plastic tray under the engine in these cars since it seems to accelerate engine wear due to the contained heat. Here are some performance exhaust improvements for street driven cars:

Air Intake Modification

Airbox modifications result in more intake noise and a tad more power. The Factory airbox and throttle body are well matched to the operating range of the stock engine.

Camshafts

There are several camshafts available for the 3.6 litre engines. Some of them are street legal such as RS cams and will pass US emissions tests, however others require a different intake system and do not pass smog checks. For cars with an ITB system, there are some sport-type cams that will make more power above 6500 RPM than the stock components.

Pistons and Cylinders

One of the best ways to increase performance in the 3.6 litre engine, regardless of model year is to install a Mahle 3.8 litre, RSR 102mm 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. Aftermarket rods such as Pauter or Carillo are required due to the piston design.

Solid Lifters

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 (above 7K), these lifters can fail so 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.

Head Flow

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 15% with some handwork. This also eliminates a major “step” where the liner meets the valve seat.

For further information about these engines and the various configurations that are possible for street and track use, contact us.