What is an Intercooler? | Revv.ly Glossary

What is an Intercooler?

Here's a fundamental principle of physics that explains why intercoolers exist: compressing air heats it. When a turbocharger or supercharger forces air into an engine, that air becomes hot--potentially very hot, exceeding 150C in some applications. And here's the problem: hot air is less dense than cool air, which means less oxygen per unit volume, which means less potential power. The intercooler solves this rather elegantly.
An intercooler is a heat exchanger positioned between the compressor outlet and the engine's intake manifold. Its job is to cool the compressed air before it enters the engine, increasing air density and therefore the amount of oxygen available for combustion. More oxygen means more fuel can be burned. More fuel burned means more power extracted. The physics are quite satisfying, actually.

The Two Types

Air-to-Air Intercoolers -- The most common type, using ambient air to cool charge air. The intercooler sits in the airstream--typically behind the front grille--and heat transfers from the hot charge air through the core's fins to the cooler ambient air passing through. Simple, reliable, no additional systems required. The limitation is that the intercooler can only cool to ambient temperature at best, and thermal efficiency depends on vehicle speed and airflow.
Air-to-Water (Liquid) Intercoolers -- Uses a liquid coolant circuit to absorb heat from charge air. The intercooler can be mounted anywhere (including on top of the engine), with a separate heat exchanger elsewhere to cool the liquid. Advantages include more consistent cooling regardless of vehicle speed, compact packaging, and potentially lower intake temperatures. The complexity and cost are the trade-offs--additional pump, reservoir, heat exchanger, and plumbing.

The Science of Sizing

Intercooler effectiveness depends on several factors:
Core Volume -- Larger cores provide more surface area for heat transfer. However, larger cores also mean more internal volume, which can increase turbo lag as the compressor must pressurize additional space.
Core Design -- Bar-and-plate cores are stronger and potentially more efficient but heavier. Tube-and-fin cores are lighter and less restrictive but more fragile. Both work when properly engineered.
End Tank Design -- How air enters and exits the core matters. Poor end tank design creates uneven flow distribution, meaning some parts of the core work harder than others. Quality intercoolers use CFD-optimized tanks for even distribution.
Ambient Conditions -- An intercooler's effectiveness varies with ambient temperature. Hot summer days stress cooling systems harder than cool autumn mornings. Track days with repeated heat soak challenge intercoolers differently than street driving.

Heat Soak: The Enemy

During extended high-load driving, intercoolers accumulate heat. The core temperature rises, cooling effectiveness drops, and charge air temperatures climb. This is heat soak, and it's particularly problematic on track days where repeated laps prevent adequate cooling between hot laps.
Larger intercoolers resist heat soak better because they have more thermal mass and surface area. This is why track-focused builds often run intercoolers far larger than strictly necessary for peak power--they're buying heat soak resistance.

The Upgrade Decision

Factory intercoolers are sized for expected use cases, with typical cost and packaging constraints. Performance applications often benefit from aftermarket upgrades:

• Lightly Modified Cars -- Factory intercoolers often suffice. Money is usually better spent elsewhere.
• Stage 2+ Builds -- Upgraded intercoolers prevent heat-related power loss. Essential for consistent performance.
• Track Use -- Larger intercoolers with better heat soak resistance maintain power lap after lap.
  Quality brands include Mishimoto, Wagner Tuning, CSF, and platform-specific specialists. The investment protects your tune and maintains consistent power delivery.
  Discuss cooling solutions with the Revvly community--the enthusiasts who've tested options on track and street.
  Related: Boost, Tune, Downpipe
  Intercooler Upgrade Platforms: Subaru WRX STI, Ford Mustang EcoBoost, Audi S3