ENGINE AND VARIORAM
The 993's 3.6-litre air-cooled flat-six developed 272bhp on launch, rising to 285bhp in its final Varioram form. This patented Porsche technology has long been a source of confusion among owners and enthusiasts, and though we’ve written about the system in previous issues of 911 & Porsche World, it’s worth us summarising how it works. Varioram is, in short, an ingenious way to alter geometry of the inlet manifold according to engine needs under different operating conditions. Intake air is fed into the manifold from the air filter, but airflow can enter two separate butterfly throttle valves. The upper valve opens by varying amounts at all times, allowing air into a central plenum distributing flow to the three runners atop the engine, which lead to what appears to be further plenum chambers with lower runners connecting to the cylinders below.
What you can’t see from the outside is that the top runners feed moveable sections, which are vacuum-operated and computer controlled. At low engine speed, they seal the top runners to the lower runners, resulting in much longer runner length, better suited to the creation of low-speed torque. At this stage, the rest of the manifold is redundant, but when engine speed reaches 5,160rpm and the throttle is more than fifty percent open, the moveable sections retract to allow air from the top runners into the lower plenum chambers.
The lower throttle valve also opens, increasing overall airflow to the engine. In this scenario, the runner length is much shorter from the lower plenums to the cylinders, which is better suited to high-speed operation and develops more power. At 5,920rpm, further changes occur, resulting in higher volumetric efficiency as the engine homes in on its peak power point.
The first engine to make use of Varioram was the 3.8-litre flat-six powering the mighty 993 Carrera RS. This was a significantly different engine to the 3.6-litre boxer propelling the same
generation Carrera and all-wheel drive Carrera 4 — the RS lump featured lighter pistons and rocker arms, along with large intake vales and a 2mm increase in bore diameter. Peak output of 296bhp at 6,500rpm and 262lb-ft torque at 5,400rpm are, understandably, usefully higher than the 3.6litre unit’s aforementioned output (delivered at 6,100rpm), the higher revs in the track-focused RS befitting its remit in life.
A more useful comparison can be made between early 993 engines and those introduced from 1996, when all 993’s benefited from Varioram. As we explained earlier, power wasn’t radically improved, but Varioram’s goal is to refine and improve torque output across the whole rev range. The 3.6-litre Varioram-equipped 993 engine also received bigger valves, which enhanced breathing, especially at the top end. Weight may have been hiked by thirty kilos, but the sprint to 62mph from rest dropped from 5.6 seconds to 5.4 seconds, with top speed increasing from 167mph to 171mph. Fuel consumption improved, too. For all these reasons, the short-lived Varioram 993 is regarded as pick of the Carreras, although it is more mechanically complex, a consideration when it comes to servicing and maintenance.
Talking of which, air-cooled Porsche engines can be expensive to repair, which is why you should be presented with documentation demonstrating regular oil and filter changes, regardless of age or the amount of ground covered — in Porsche circles, maintenance trumps mileage. Paperwork from recognised independent marque specialists or Official Porsche Centres will contribute to maintained value.
Lack of proof may be reflected in the asking price, but keep in mind few cars are as expensive as a ‘cheap’ 911. Thankfully, most 993 oil leaks are easy to fix, but check the oil temperature gauge on your test drive — a high reading suggests the oil cooler fan may be non-operational. It’s a timeconsuming repair, even though replacement parts are reasonably priced from independent retailers.