Ford contributed numerous firsts to the car industry, from the first mass-produced V8, the kickstarting of the muscle car era with the Mustang and the only American car company to beat the Europeans at Le Mans with the GT40. Fast-forward a few decades, and we now have highly engineered hot hatches in the form of the Focus ST, turbo and supercharged (track-only) trucks and cars embodied in the F-150 Raptor and Dark Horse Mustangs. While there’s a comprehensive lineup of current models to suit a range of drivers, the discontinued yet performance-ready Focus ST still offers a balance of power and value, making it a fan favourite.
Production may have stopped in 2022, but anyone lucky enough to drive an ST knows its potential. The turbocharged 2.3-litre EcoBoost churns out a whopping 280hp from only four cylinders, with the car speeding to 60mph in under 6 seconds. What Ford die-hard fans already know is that a few tweaks are all it takes to cut seconds off from fast runs and propel the car well beyond the limited top speed of 155mph.
Changing the turbo is one (expensive) option; the other is fitting a more efficient intercooler for Focus ST. This cools compressed air from the turbo before it is pushed into the engine for combustion. The benefits are numerous, including a car that’s more responsive to the throttle and power gains of up to 10 per cent.
Intercooler Basics
Mounted behind the grille, and between the turbocharger and engine, an intercooler acts as a heat exchanger, cooling down compressed air before it is pushed into the engine and combusted with fuel. Intercoolers are critical parts in engines with forced induction, helping overall engine efficiency and preventing overheating. Besides regulating air temperature, the component also helps compress the oxygen from the turbocharger into a more consumable form, thus improving turbo spooling.
Main Types
Focus ST intercoolers come in different guises and types, each with its own application and set of advantages:
Air-to-Air Intercoolers
These are standard types found in most production cars and trucks. They pass compressed air from turbochargers or superchargers through a network of fins or coils. These parts dissipate heat (much like a radiator does), cooling the air. The simple, cost-effective design and lower weight are more than adequate in factory engines, resulting in much improved engine efficiency with a significant power boost.
Air-to-air intercoolers come in two types. Front mount variants (like those fitted in the ST) consist of more complex parts and plumbing, but also offer better cooling and higher efficiency for bigger power gains than comparable top mount types, which are prone to more heat soak from hot engine parts.
Air-to-Water
This type uses water to cool the air from the turbocharger or supercharger, and provides a denser charge than air-to-air types for higher power gains and more efficient cooling. While more complex in design and more costly, air-to-water intercoolers are chosen in cars with limited space in the engine bay, while still offering more stable temperature regulation. The intercoolers, however, are included as part of a tuning kit that also has revised radiator designs, pumps, and plumbing. And unlike air-to-air intercoolers, these perform regardless of where they’re fitted.
Differences Between Stock and Aftermarket Intercoolers
The main difference between a stock and aftermarket intercooler for Focus ST is that the aftermarket version features a larger core for improved cooling capacity. If you’re modding the ST with other power parts, such as faster spooling turbos or performance cams, aftermarket intercoolers perform better by simply being bigger.
Another key difference is larger inlet and outlet diameters, meaning higher air volume and mass flowing entering and exiting the intercooler. Core design also differs, with more parameters that tend to higher flow capacity. Lastly, most aftermarket manufacturers move away from the factory plastic end tanks prone to damage and cracking to aluminum end tanks for higher, leak-free durability.
Upgrading Your Focus ST with the Right Aftermarket Intercooler
If you’re looking to increase the stock power numbers from the 2.3-litre EcoBoost engine with performance cold air intakes, aftermarket exhausts, and an ECU tune to balance things out, then you’ll need a bigger aftermarket intercooler. Increased power also means increased heat, and the stock intercooler won’t cope with the higher output well before leaks, clogging or damaging fins and cores become a problem. This is mainly due to raised inlet temperatures and increased boost pressure, often resulting in counterproductive power loss or even dangerous engine detonation.
To restore reliability, all new parts, including intercoolers, need to be evenly matched. A major buying consideration is core size, inlet and outlet diameters to ensure proper airflow in and out of the component. Designs and construction are other considerations. Aftermarket types gravitate toward more efficient bar-and-plate intercoolers, being more efficient than standard types with tubed or fin designs.
A highly-tuned Focus ST will also benefit from a larger water-to-air system, with improved heat dissipation and sturdier end tank materials for proven performance. Once you’ve decided which type suits your stock or modded Focus ST, also consider a professional fit to reap the benefits of increased power, higher engine efficiency, improved durability and a car that’s even more fun to drive.
