Intercooling Plan of Attack - Part One

This article was first published in 2003.

Installing an intercooler is like any other major Do-It-Yourself project - for the best results you should first put together a plan of attack.

There are a number of factors that should be considered when fitting a 'cooler. Ask yourself how much money and effort you're prepared to invest. Think about the cooling performance of a specific set-up in various conditions. Will charge-air flow restriction be an issue? Is it likely that radiator performance will be significantly affected? Does mounting a 'cooler in 'position X' hinder access to the dipstick or other servicing points?

Obviously there's a lot more to this intercooling caper than grabbing a second-hand core from a mate and cramming it in wherever it'll fit... Let's consider each of the above factors one by one.

How Much Will It Cost?

If you have plenty of cash available you might decide to have a shiny new intercooler installed by a performance workshop. If this is the case, read no further.

But if this isn't the case, the first thing you should decide is how much money you're prepared to spend. This will determine the sort of intercooler you can afford and whether you can afford an electric cooling fan and/or a water spray system.

The intercooler is typically the most expensive part of an intercooler system. As we've mentioned in previous articles, the best value intercoolers on the market are second-hand units available from Japanese import wreckers. Medium size air-to-air 'coolers will set you back AUD$150-300 and allow enough charge-air flow for around 200kW. The larger OE intercoolers from Japan - such as those fitted to the Toyota 1JZ twin-turbo and Mitsubishi Evo Lancer - fetch anywhere up to AUD$750. These are suitable for engines generating 250 - 300kW.

See The World's Biggest Intercooler Comparison - Part One for our comparison of twenty-five Japanese import intercoolers.

Brand new aftermarket intercoolers are available in all shapes and sizes and are generally reserved for more expensive installations. Prices vary depending on brand, construction and size, but aftermarket units usually cost anywhere between AUD$800 and AUD$2000. The more expensive examples perform well at power outputs beyond 500kW.

Now let's look at the other costs associated with fitting an intercooler.

Intercooler plumbing is the pipework that takes charge-air from the turbo to the intercooler and then to the engine. This plumbing is normally the second-most expensive part of the job. Intercooler plumbing can be quite effectively done on a budget (as discussed in Part Two), but if doing the pipework looks too hard, you might decide to offload the job to a performance workshop. Depending on the amount of plumbing required, a workshop shouldn't charge any more than about AUD$400. (Typically, this price doesn't include polishing.)

The other costs you'll encounter are fairly minor. You'll need some steel to make mounting brackets for the intercooler, some plastic or alloy sheet for ducting outside air through the core, and you might need to pay a few dollars to weld on a blow-off valve or idle air fitting. The total of these items will be less than AUD$50.

Depending on where you decide to mount the intercooler, you might also need to pay for an electric cooling fan and/or a water spray system. Twelve-volt automotive fans typically range from about AUD$30 (second-hand) to AUD$180 (new) and water spray systems vary even more depending on the pump and control system employed. A basic water spray system will cost about AUD$50 while a full-blown brand name system can cost several hundred dollars. (See Part Two of this series for details on cooling fans and water sprays.)

The Intercooler - Which One To Buy?

The first step when picking an intercooler is to think about how you use your car.

If you plan to dabble in some circuit racing or expect to spend time on a dyno it's advisable to pick an intercooler with standout cooling performance. This will maintain stable intake air temperatures and minimise the risk of engine damage. On the other hand, a car that rarely sees sustained turbo boost can benefit from an intercooler with slightly less cooling performance but that has relatively high thermal mass and minimal charge-air flow restriction. Thermal mass is important for absorbing short duration boost periods, while minimal charge-air flow restriction gives good throttle response and top-end power.

Of course, an intercooler with good cooling performance, good thermal mass and good charge-air flow is ideal, but it's useful to know which way to err should you need to make a choice.

	Charge-Air Flow (cfm)	Thermal Mass (kg)	Core Volume (litres)
Mazda Series 4 RX-7	212	2	2.931
Mazda Series 6 RX-7	310	2	2.186

This table shows the important characteristics of two similarly-sized intercoolers. Based on the criteria of flow, thermal mass and core volume, the Series 4 intercooler would be more suited to a circuit sprint vehicle. On the other hand, the high-flowing Series 6 intercooler would provide best 'traffic light performance' in a streetcar.

The Intercooler - Where to Mount It?

At this point, it makes sense to also think about where you'll be mounting the intercooler and whether you'll be adding an electric cooling fan and/or a water spray.

Mounting the intercooler directly above the engine (aka top-mount) typically limits the amount of space to fit a large core. A hole through the bonnet, a large forward-facing scoop and an airtight seal against the intercooler core are also necessary to provide the ambient airflow that cools the charge-air. Note that the cooling performance of a top-mount intercooler is hampered by under-bonnet heat-soak in stop-go traffic conditions. This can be remedied by fitting an electric cooling fan to draw ambient air through the core when the car is stationary or moving at low speed. But often there isn't enough space to fit a fan between the intercooler and the engine. Another downside is impaired access to spark plugs, etc.

There is only one benefit to mounting an intercooler directly above the engine - the intercooler plumbing can be kept short. This maximises charge-air flow, keeps lag to a minimum and is simpler from an installation point of view.

However, the downsides of top-mounts usually outweigh the positives - we suggest that wherever possible, you pick another intercooler location.

A variation on the above approach is to mount the intercooler under the bonnet but not directly above the engine, called a side mount. A side mount gives you more space to fit a slightly larger core. It also allows more space to fit an electric cooling fan on the underside of the intercooler. We've seen these arrangements perform very well on street cars, but you will still need to cut a hole through the bonnet, fit a scoop and seal it to the core. Mounting the intercooler in this location may also block access to the clutch adjustment mechanism, fuel filter or other servicing points.

The benefits of short intercooler plumbing remain and usually this is a much better mounting position than directly above the engine.

If you want to squeeze in the largest possible intercooler you'll need to mount it inside the nosecone (aka front-mount). Depending on the size of the cooling aperture in the front bumper, this location generally provides the greatest volume of ambient airflow and the heat soak issue is relatively insignificant. Expect only a small amount of heat from the radiator to warm the intercooler in stop-start conditions whenever the radiator fan is switched off. However, when the radiator fan switches on, ambient air is drawn through the intercooler, keeping it cool. Another positive is that a front-mount intercooler maintains easy access for engine servicing.

The downside of this mounting position is the relatively long intercooler plumbing that's required. This causes charge-air flow restriction, lag and complex pipework. Note that mounting an intercooler in front of the radiator may also cause engine overheating.

Overall, though, a front-mounted intercooler is desirable.

A variation on this configuration is to mount the intercooler inside the wheel arch cavity forward of a front wheel. This location offers less intercooler space than found in the nosecone, but you can often still fit quite a large unit. For example, the 1JZ-GTE Toyota Soarer intercooler is designed to fit inside that vehicle's front left guard and offers very good charge-air flow and cooling performance for applications up to 250kW.

Note that - unlike an intercooler mounted in the nosecone - a guard-mounted intercooler will not increase the likelihood of engine overheating. Again, though, there is a considerable amount of plumbing required and you'll also need to fabricate a forward-facing cooling duct from the bumper. This is an attractive mounting location for all but extreme power applications where you want to fit the largest intercooler possible.

	Intercooler Mounting Location Pros and Cons At a Glance...
Top-Mount (Directly above engine)	Pros: - Allows short intercooler plumbing for minimal restriction and lag Cons: - Extremely limited space for the intercooler - Severe low-speed heat soak - Typically impairs access to spark plugs, coils, etc - Requires fitment of a large bonnet scoop and an air-tight seal against intercooler core
Top-Mount (Not above engine)	Pros: - Allows short intercooler plumbing for minimal restriction and lag Cons: - Limited space for intercooler - Electric cooling fan required to avoid low-speed heat soak - Typically impairs access to clutch adjustment mechanism, fuel filter, etc - Requires fitment of a large bonnet scoop and an air-tight seal against intercooler core
Front-mount (In front of radiator)	Pros: - Allows fitment of biggest possible intercooler - Excellent cooling airflow - Maintains easy access to servicing points Cons: - Reduces cooling airflow through radiator - Relatively long intercooler plumbing required (adds restriction, lag and can be difficult to route)
Front-mount (Inside wheel arch)	Pros: - Allows fitment of relatively large intercooler - Excellent cooling performance when fed by a forward facing duct - Maintains easy access to servicing points Cons: - Relatively long intercooler plumbing required (adds restriction, lag and can be difficult to route)

Stay tuned for the second of this two-part series - we look at intercooler plumbing, easy steps to improving intercooler performance and more!