Friday 12th November 2010

Porsche 993 Buying Guide - Powertrain

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There are several versions of the rear-mounted, horizontally opposed six-cylinder engine used in the 993. For the basic Carrera models, they can be easily divided into pre-Varioram and Varioram units, though both can run on 95- and 98-octane unleaded. The original 3.6-litre M64 flat-six came with lighter pistons and connecting rods than the 964 model’s, and there was a stronger crankshaft too. Each bank of three cylinders has a single overhead camshaft driven by a chain, with two valves per cylinder and Bosch Motronic M2.1 engine management. This created 272bhp at 6100rpm and 243lb ft of torque at 5500rpm.

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In September 1995 for the 1996 model year, Varioram was added to the Carrera’s engine after it was first used on the RS that was launched earlier in ’95. Along with larger intake and exhaust valves, Varioram upped power to 285bhp and swelled torque to 251lb ft at a slightly lower 5250rpm. Varioram works by altering the length of the inlet pipes depending on engine speed. Below 5000rpm, the inlet pipes of a Varioram-equipped car are about twice the length of an earlier 993 model’s. Above 5000rpm, they shorten by means of a vacuum-operated sleeve. A Varioram-equipped 993 is easy to spot by opening the engine lid and looking for the large aluminium pipes sat on top of the engine. In non-Varioram 993s, there’s a much smaller black-painted system of pipes.

When looking in the engine, it’s also worth checking out the air conditioning pump is on good order. Sat just to the right of the distinctive fan, the pump’s belt should be in good condition and taut.

Any signs of an oil leak in a 993’s engine bay should be a cause for concern. These engines are tough and long lasting, but regular oil changes are essential and owners shouldn’t necessarily wait till the 12,000-mile or 12-month service interval to come around. As the oil is also used to help cool the engine, it must be at the right level. As the engine is a dry sump unit, with the oil tank mounted in the offside rear wing, the engine must be fully up to temperature before the oil level is checked on the dipstick. Any smoke from the engine when it’s started from cold should also act as a warning sign.

While checking the engine, look at the heat exchangers as they can rust and are expensive to replace. Plenty of 993 owners will have replaced the original exhaust with a sports item, but make sure it will pass an emissions test for the MoT.

The Turbo and GT2 use the same basic engine as the Carrera models but with twin KKK K16 turbochargers and Bosch Motronic 5.2 engine management. The compression ratio increased from the 964 Turbo’s 7.5:1 to 8.1 and the Turbo could now run on regular 95-octane petrol rather than just 98-octane fuel. The GT2 upped power further to 450bhp for the race cars, while roadgoing GT2 came with 430bhp. A handful of road legal GT2 Evos were made with 450bhp engines, giving a top speed of 189mph and 0-60mph in 4.4 seconds. The Turbo was good for 0-60mph 4.5 seconds and 180mph. Only the RS model used the larger 3.8-litre capacity flat-six engine, packing 300bhp.

All rear-wheel drive 993 models used the six-speed manual G50 gearbox as standard, while the Tiptronic was an A50 unit. The Turbo came with a six-speed G64 gearbox.

Buying Guide Index:

Porsche 993 - Introduction
Porsche 993 - Powertrain (viewing now)
Porsche 993 - Rolling Chassis
Porsche 993 - Body
Porsche 993 - Interior
Porsche 993 - General Experiences
Porsche 993 - Insurance (Sponsored link)

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[RRG]

My comments relate to N/A cars only.

The engines are generally very robust and I've heard of cars exceeding 250,000 miles without rebuild.

Two general things to look for;
1. The cam covers are made from plastic and can warp / crack with the heat from the exhaust over time. They then start weaping oil, usually onto the exhaust manifold. Symptoms are a whiff of oil when you stop the car after a run, sometimes even in the cabin. It's not a big deal to sort it out just fiddly due to access.
2. In the late 1990s, there was a recall to replace the engine wiring loom. Some cars were not reconnected properly, leaving the Varioram permanently inoperative. My RS suffered from this and I got an extra 40bhp simply by getting the connections sorted! Symptoms are rather lacklustre performance over 4,500rpm.

More specific to the RS;
lots of RS cars have been thrashed on tracks and this has brought the following to light in what is otherwise an extremely robust unit:
1. Cam timing: the cam drive wheel is not keyed onto the camshaft (very odd omission from the factory) and it can slip slightly resulting in the cam timing falling out. Symptom is modest reduction in power output. There is a simple upgrade available to deal with this - worth checking if the car has had it fitted.
2. Valve retainers: can break on thrashed engines causing valve to meet piston very expensively. There is an upgrade available (titanium retainers) and again, worth checking if the car has it fitted.
3. Cylinder liners: bit of an odd one this. It appears that a batch of cars have out of spec liners fitted which allow compression blow-by at high rpm. The symptoms are serious oil leaks due to the crank case getting pressurised and serious loss of power at high rpm. The only solution is an engine rebuild with the correct cylinder liners. Maybe someone can throw more light on which cars are affected?

I've owned my RS for seven years now and covered 60,000km in it and have had none of the above issues but then again most of the miles have been on the road, not the track. However, I've had the upgrades 1 & 2 done for peace of mind. At 115,000km it still produces a nice round 300bhp.