Intercoolers FAQ

Hey chaps, bit of a continuation from my general 16VT guide, info isn’t just mk1 specific either!

First off, what is an intercooler?
A pretty easy question but one that some members might not know. An intercooler (or aftercooler if you’re old ) is essentially an air radiator that is designed to cool the compressed air from the turbo or supercharger fitted to your vehicle. There are a variety of methods to cool the charge air down but the principles are the same. Hot air goes in one pipe, it enters multiple cores which have finned heat sinks between them to increase surface area and thus to increase heat dissipation and cold air comes out of another pipe. This colder air is denser and richer in oxygen then the hot air, and by the laws of internal combustion, the more air you add the more fuel you can add, the greater the combustion of the mixture is and the more power you get! Colder air also decreases the chance of pre-ignition and damaging the engine internals (as does higher octane fuel), allowing you to run greater ignition advance and boost pressure!
Single or twin pass?
Many aftermarket companies make intercoolers that are both single pass and twin pass. Single pass intercoolers, as the name suggests, lets the air pass through it once. Air flows through one end, is cooled via the cores, and then has an exit for the cold air on the opposite side. Most factory fitted intercoolers are single pass
A twin pass intercooler lets the charge air flow through the intercooler twice. Both inlet and outlet pipes are located on the same side, cooling down the charge air twice.
However, it must be considered that with an intercooler there is a trade-off between cooling ability and pressure drop. With a twin pass intercooler, the air has to essentially travel twice the distance than the air in a single pass intercooler. Whilst this results in lower ACTs, there will be a noticeable pressure drop (around 1-2psi) so boost pressure will have to be raised. If your car has a fairly small or standard turbo running low boost a single pass intercooler would be ideal due to the fact that there is a lot less air to cool than a larger turbo. If you’re running a large turbo with some pretty big boost a twin pass would be far more efficient, with the pressure drop offset by the increased cooling.
What is a charge cooler?
A charge cooler is the opposite of a radiator. It is basically a water jacketed intercooler. A charge cooler is far more efficient than an intercooler of an equivalent size as water has a thermal conductivity about 3 times that of air and can further lower Air Charge Temperatures. The drawback of this system is that obviously it is far more complex and heavier that a standard intercooler as components such as pipes, lines radiator and a water tank must be installed in the vehicle.
Installing in the vehicle
Most aftermarket intercoolers I’ve seen (especially in the mk4 golf scene) is just a standard eBay job stuck behind the front bumper. Whilst this might look cool, half the time 40% of the cores and fins of the intercooler are blocked by the bumper or other parts, with little consideration given (if any) to the reduced airflow to the radiator. A front mount intercooler can rapidly raise engine temperatures if you have a defective radiator or cooling system everything can get pretty toasty! When fitting a front mount, ensure that as much intercooler core is exposed to the outside air (drilling holes in bumpers is a common solution or cold air feeds from foglight holes). A slimmer, high flow fan may be required to pull more air into the radiator. Lower temperature thermostats and fan switches are also a good idea!
Anyone with any more info please feel free to add/correct this post, will add some more info later on!

Nos

Thanks for this write up, you've just answered a lot of questions that we're going through my mind. Being a bit of a novice I didn't even know what the ic purpose was. I'll be sure to get some extra air flow to my radiator somehow(probably with extra air scoops behind grille)as the ic I bought is quite tall and cuts off more than half of
the rad.

No worries fella. Gimme a shout if you need any more info!

Will do Nos

Great post Ahmet, I feel like I've been to school today and learnt something