On the 991 Turbo, the charge air coolers sit in the rear quarters, one per bank, and they work as a pair. Splitting the path keeps the pipe runs short and lets each core sit where there is a natural supply of air from the quarter vents. It is an efficient layout on a car where the engine bay is already full.
Working on the arrangement means accepting the constraint rather than fighting it. There is no useful space to move the coolers somewhere else, so the gains come from making the existing positions work better.
A larger core adds material, surface area and internal volume. Each of those changes something different. More surface helps the core shed heat, but more internal volume also has to be filled before the manifold sees pressure, which is why a poorly matched large core can feel softer than the part it replaced.
The trick is to keep the internal path sensible while gaining the surface area. That is a question of core choice and end tank shape, not simply of picking the biggest part that fits.
The end tank is where charge air enters and leaves, and its internal shape sets how the air distributes across the core face. A tank that dumps air straight at one corner gives that corner the most flow and leaves the rest of the core working less hard than it could.
Hand-welded aluminium tanks let us shape the transition so the air spreads more evenly. That is the part of the job we spend the most time on, and it is the part that is hardest to see once the car is back together.
With two coolers there is a pipe run across the engine bay, and that run is usually the least symmetric part of the system. If the two sides do not see similar pressure drops, the banks behave differently under load.
The way the pipe crosses the bay, the number of bends and the position of each joint all affect that balance. Where the factory part makes an awkward turn, a custom pipe can often take a cleaner route and reduce the number of connections at the same time.
Fewer joints means fewer places to leak, and fewer places for a hose to work loose over time. We treat every connection as a future maintenance point.
The coolers only work as well as the air reaching them. On the 991 the quarter vents feed the cores, and the shroud around each core has to keep that air on track. Any gap between the shroud and the bodywork lets air take the easy way past the cooler instead of through it.
An owner who uses the car mainly in traffic notices something different from an owner who drives it hard on open roads. In slow traffic the core soaks in engine heat, and the value of a well-sealed shroud is that the core starts recovering as soon as the car is moving again. The shroud and the seal are therefore worth as much attention as the core itself.
This is why we treat the ducting as part of the kit rather than an accessory. The core, the shroud and the feed all have to be considered together, and the result is judged on the car rather than on the bench.
Between the aluminium parts there are flexible joints, and on a rear-engined car those joints see plenty of movement. The engine rocks under load, the body does too, and a rigidly clamped connection will not tolerate both.
Reinforced silicone with enough plies to hold its shape under pressure is the answer. It also has to be positioned so the clamp sits square, because a clamp on an angled joint is the most common cause of a hose that will not stay put.
We build custom intercooler work for the 911 range alongside intake and charge parts, so the joints are designed with the rest of the system in view rather than in isolation.
Every mould and every assembly is tested before it goes further. For intercoolers that means checking the fit of the tanks, the alignment of the mounting points and the way the whole unit sits against the ducting.
We measure the finished part and check it against the drawing. Where a sample is involved, it goes to the customer before mass production starts, which is the point where small changes are still cheap.
Two questions decide most of the specification on a 991 Turbo build. The rest follows from them.
We will ask for photographs of both sides of the engine bay. That single set of images answers more than a page of description and shortens the whole process considerably.
The 996, 997 and 991 all appear in our intercooler range, and the differences between them are worth understanding before you commit. It also helps to read the BMW, Audi and Porsche listings as a set, look at the intake side on air intakes, follow the joints through performance silicone hose, and see the sections that connect everything on our exhaust pipe page.
