The World's Biggest Intercooler Comparison - Part One

Intercooling - there's an expensive way to go about it and a cheap way to go about it. If (like us) you find paying $2000-odd for a glorified heat exchanger a little exorbitant, chances are you'll find gold at your local Japanese importer. Japanese importers are a great place to shop for second-hand 'coolers from Japanese domestic market (JDM) vehicles - it's not uncommon to see racks chock full of bargain intercoolers.

The big question is: which of these intercoolers is the best in terms of flow and thermal efficiency? This comparison - the largest of its sort we've seen anywhere in the world - will give you all the answers...

How We Tested the Intercoolers

To compare the airflow capacity of our twenty-five Japanese intercoolers (twenty-four second-hand and one brand new) we called upon the services of a local flow bench operator - Frank Intini of F&M Cylinder Heads. We reused the flow bench adapter employed in our previous Subaru Top-Mount Trial (see "Top-Mount Trial - Part One") and fabricated a few tapered tubes to cater for the different intercooler pipe diameters. These tapered tubes were clamped to the end of the flow bench adapter as required.

To identify the optimal flow direction for each intercooler we measured the airflow in both directions through the core. This gives the best possible flow figure for each intercooler and provides handy guidance for those people who might install one of these units. Airflow was measured with the flow bench pushing air through the core - we simply swapped the intercooler end-for-end to obtain the second flow figure. Note that flow figures are quoted in cubic feet per minute (cfm) and were obtained at 28 inches of water test pressure.

The heat exchange performance of an intercooler is difficult to quantify without on-car testing. However, as a guide, we measured the volume of the heat exchange core and weighed each bare intercooler (stripped of all rubber mounts, removable pipes etc).

The volume of the heat exchange core (the section comprising the cooling fins only) is a guide to the amount of contact the heated charge-air has with cooling air. The larger the core volume, the better the charge-air can be thoroughly cooled.

The mass of an intercooler is important because it represents the thermal mass of material that charge-air heat can be transferred to. A greater mass generally means greater heat-sink ability - and that's important for a typical road car that cops the occasional short squirt. On the other hand, note that it is possible for a high thermal mass to work against you in some installations. For example, if an air-to-air intercooler is mounted in the engine bay, it will become heat-soaked in stop-go traffic conditions. The core must then be cooled before it can effectively transfer charger-air heat.

Combine all these aspects and you have a reasonable guide to intercooler heat exchange performance.

Why You'd Want a Second-Hand Japanese Intercooler Second-hand Japanese intercoolers are quite simply the most cost-effective way to intercool your turbo or supercharged streetcar. Whether you're force-inducting a factory NA motor or improving an existing intercooler arrangement, imported cores offer unrivalled value for money. Many sizes are available to suit your power requirement (up to 300kW isn't a problem for some of the better examples) and there are numerous shapes to suit the available space in you car's nosecone. In many instances, second-hand import cores also come with handy mounting brackets attached. All this for typically between AUD$100 and $500!

Test Results

BFMR Mazda 323 B6 Turbo Air-to-Air Intercooler

Flow - Direction A and B 178 cfm (equal 22^nd overall)

Mass - 1.15kg (24^th overall)

Core Measurements - 28.0 x 13.0 x 6cm = 2184cm3 (20^th overall)

Factory-fitted on the 103kW 1.6-litre turbocharged Mazda 323, this relatively light-duty all aluminium intercooler has the second lowest thermal mass of the twenty-five 'coolers on test. On the flow bench it's beaten by many of the other smaller intercoolers, but given its overall size, it does offer a decent core volume .

Steer away from this intercooler except where space is limited and you expect to make less than 110-120kW.

BG8Z Mazda Familia GTX Turbo Air-to-Air Intercooler

Flow - Direction A (air entering larger diameter pipe) 247 cfm (6^th overall)

Direction B (air exiting larger diameter pipe) 245 cfm

Mass - 1.2kg (23^rd overall)

Core Measurements - 25.0 x 12.5 x 6.4cm = 2000cm3 (24^th overall)

Replacing the 1.6-litre turbocharged Mazda 323 is the Japanese market Mazda Familia GTX (body code BG8Z). Using a larger 1.8-litre turbo engine producing 134kW, the Familia GTX's all aluminium intercooler flows incredibly well for its size - better than a big Pulsar GTi-R intercooler, for example. On the other hand, its core volume ranks second last and its thermal mass ranks third last.

Give it extensive core ducting, a water spray and maybe a cooling fan and this is a great little intercooler for medium power applications. See "DIY Budget Intercooler Fitment" for an installation example and details on how to enhance its heat exchange performance.

BG8Z Mazda Familia GTR Turbo Air-to-Air Intercooler

Flow - Direction A (air entering smaller diameter pipe) 190.8 cfm (18^th overall)

Direction B (air exiting smaller diameter pipe) 181 cfm

Mass - 2.4kg (12th overall)

Core Measurements - 23.5 x 22.5 x 6.4cm = 3384cm3 (11^th overall)

The rally-ready version of the 1.8-litre turbo Mazda Familia is the 154kW GTR. The larger aluminium intercooler seen here is reputedly part of the reason why the Familia GTR cranks out an extra 20kW, but our figures show it's not such a hot item as its reputation suggests... Surprisingly, this intercooler is more restrictive than the GTX item with a cfm ranking in the lower half of the field. It appears Mazda was prepared to sacrifice some intercooler flow in order to improve the heat exchange properties of their GTR - core volume and thermal mass are much improved over the GTX, but still middle-of-the-road amongst the twenty-five 'coolers tested.

This is a good intercooler for low to medium power applications - no need to bother with water sprays etc. On the other hand, it's too restrictive to use on engines making more than about 150kW.

Mazda RX-7 Series 4 13B Turbo Air-to-Air Intercooler

Flow - Direction A (air entering longer pipe) 212 cfm (equal 11^th)

Direction B (air exiting longer pipe) 202.4 cfm

Mass - 2.0kg (equal 17th overall)

Core Measurements - 29 x 16.3 x 6.2cm = 2931cm3 (equal 13^th overall)

The first turbocharged Mazda RX-7 sold in Australia was the 136kW Series 4 13B-T. Thanks to the availability of local wrecks and imports, the all-aluminium Series 4 RX-7 intercoolers are currently fairly easy to find. On the flow bench the S4 'cooler rated equal 11^th, tying with the Toyota 1G and Daihatsu GT-ti intercoolers. Its core volume and thermal mass is beaten by the Toyota 1G, which keeps it away from the top of the field in the medium size intercoolers.

Another capable all-round intercooler but it could be improved with core ducting and water spray. We'd recommend using it on engines making comfortably more than 150kW.

Mazda RX-7 Series 5 13B Turbo Air-to-Air Intercooler

Flow - Direction A (air entering longer pipe) 238.5 cfm (7^th overall)

Direction B (air exiting longer pipe) 231.3 cfm

Mass - 2.0kg (equal 17th overall)

Core Measurements - 29 x 16.3 x 6.3cm = 2931cm3 (equal 13^th overall)

The Series 5 RX7 intercooler is identical to the Series 4, except it has a couple of small 'trim' differences, a slightly different end-tank and a larger diameter entry pipe (the longer pipe). Primarily thanks to its larger entry pipe, this 'cooler flows better than the Series 4 reaching an impressive 7^th overall ranking on the flow bench. Aside from that, though, it's identical to the Series 4 intercooler.

A good intercooler for 200+kW power applications so long as you add a water spray etc.

Mazda RX-6 Series 6 13B Twin-Turbo Air-to-Air Intercooler

Flow - Direction A and B 310 cfm (2^nd overall)

Mass - 2.0kg (equal 17^th overall)

Core Measurements - 29.5 x 11.4 x 6.5cm = 2186cm3 (19^th overall)

With the twin-turbocharged Series 6 RX7 pushing out a creditable 190kW, it has an obvious need for good intercooler flow. As such, the Series 6 RX-7 intercooler uses large diameter pipes and a relatively small core to achieve a brilliant flow figure - only the giant aftermarket intercooler beats it on the flow bench. If you want a cheap core with abundant airflow this is it! On the other hand, the Series 6 RX7 core volume and thermal mass rate in the lower half of the field. Plastic end tanks are fitted.

If you install a Series 6 RX7 intercooler to your car, make sure you add ducting, a water spray and maybe a cooling fan - you'll have a top performer for applications in excess of 250kW.

Mazda Cosmo 20B Twin-Turbo Air-to-Air Intercooler

Flow - Direction A and B 283 cfm (3^rd overall)

Mass - 3.0kg (9^th overall)

Core Measurements - 32.3 x 17.0 x 6.5cm = 3569cm3 (9^th overall)

One of the gruntiest production rotaries of all time is the 206kW twin-turbo 20B triple-rotor, as fitted to the Mazda Cosmo. The car is fitted with the all aluminium intercooler seen here - and it's a beauty if you can stumble across one. Airflow is brilliant (bettered only by the aftermarket and Series 6 RX-7 intercoolers) and its heat-exchange properties are comfortably in the leading half of the field. It's great for flow and cooling.

If the Series 6 RX-7 intercooler is too marginal in heat exchange performance but you still want maximum flow this is the intercooler to buy. Be confident using it on engines making over 250kW.

Mazda GD MX-6/626 F2 Turbo Air-to-Air Intercooler

Flow - Direction A and B 178 cfm (equal 22^nd overall)

Mass - 2.1kg (equal 15th overall)

Core Measurements - 32.8 x 16.5 x 6.4cm = 3464cm3 (10^th overall)

Largely forgotten in the Australian performance scene is the 108kW Mazda-developed F2 turbo 2.2-litre as found in GD 626/MX-6 turbo and the late Ford TX5 Turbo. The F2 intercooler is solidly constructed in aluminium and offers mid-range core volume and thermal mass. Its airflow is very poor, however, with even the small Nissan intercoolers causing less restriction.

The only application this intercooler is suitable for is where engine output is under about 120kW.

Unknown Turbo Diesel Light Truck Air-to-Air Intercooler

Flow - Direction A and B 193.7 cfm (17th place)

Mass - 5.8kg (2^nd overall)

Core Measurements - 34.5 x 39.0 x 5cm = 6728cm3 (2^nd overall)

Not much is known about this one apart from that it came off a Mazda turbo diesel light truck. It is, however, fairly typical of the intercoolers found on similar light trucks. Ruggedly constructed in aluminium, the thermal mass and core volume of this unit is bettered only by the big aftermarket front-mount. There's certainly ample cooling potential. Unfortunately, it flows poorly making it unsuitable for big horsepower.

Use it in applications up to about 150kW and enjoy the benefits of its tremendous cooling performance.

Japanese Market Mitsubishi Galant VR4 Air-to-Air Intercooler

Flow - Direction A and B 184 cfm (20^th overall)

Mass - 3.4kg (6^th overall)

Core Measurements - 19.7 x 41.5 x 6.5cm = 5314cm3 (6^th overall)

You may not be aware that the Japanese domestic market 151kW Mitsubishi VR4 received a much larger front-mount intercooler than the Australian delivered variants. But is it really a 'gun' performer? Both the JDM VR4 core volume and thermal mass are very impressive, but the flow bench reveals its major shortcoming - it's outgunned by 80 percent of the field.

This is another good intercooler from a heat exchange perspective, but lacks the flow to make it suitable for genuine high performance. Keep its flow limitation in mind if you're looking to tweak an Aussie VR4.

Mitsubishi Lancer 1.8-litre GSR Air-to-Air Intercooler

Flow - Direction A 168 cfm (24^th overall)

Direction B 155 cfm

Mass - 1.5kg (22^nd overall)

Core Measurements - 15.0 x 24.0 x 6.4cm = 2304cm3 (17^th overall)

This is the intercooler fitted to the 141kW Mitsubishi Lancer GSR 1.8-litre AWD turbo - and it's an absolute shocker. Ranked bottom of the pile in thermal mass and airflow, its middle-of-the-road core volume is not nearly enough to redeem it.

Ignore this intercooler except if you're looking to intercool a little Japanese Kei class vehicle - or maybe a hot motorcycle.

Daihatsu Charade G100 GT-ti CB70 Air-to-Air Intercooler

Flow - Direction A and B 212 cfm (equal 11^th overall)

Mass - 1.9kg (equal 20th overall)

Core Measurements - 17.0 x 20.5 x 6.2cm = 2161cm3 (21st overall)

The mighty 78kW 3-cylinder Daihatsu Charade GT-ti engine is a pretty highly tuned bit of gear - as indicated by its impressive little intercooler. On the Superflow bench the GT-ti intercooler shocked us by putting more than half of the field to shame - 11^th position is a great result for such a compact unit. Unfortunately, from a heat exchange perspective, its core volume and thermal mass are amongst the lowest on test.

If space is tight and you're looking for up to about 120kW we'd certainly suggest combining this intercooler with a water spray etc.

Holden/Isuzu Piazza 4ZCI Air-to-Air Intercooler

Flow - Direction A 233 cfm (9^th overall)

Direction B 226 cfm

Mass - 3.3kg (7^th overall)

Core Measurements - 26.0 x 16.7 x 7.0cm = 3039cm3 (12^th overall)

While the Holden/Isuzu Piazza is seen as something of an oddity its all-aluminium intercooler is very attractive for conversions. The Piazza intercooler managed a top 10 finish on the flow bench and a very impressive thermal mass rating. Core volume j-u-s-t scrapes in at the front half of the field, indicative of this intercooler's compact dimensions.

An exceptional compact intercooler for applications approaching 200kW.

Suzuki Cappuccino F6A Air-to-Air Intercooler

Flow - Direction A and B 113 cfm (25^th overall)

Mass - 0.8kg (25^th overall)

Core Measurements - 10.8 x 18.0 x 5cm = 972cm3 (25^th overall)

Designed to cool the charge-air temp of the 660cc 3-cylinder Suzuki Cappuccino, this miniature intercooler is no use for much else. It scores last across the board - thermal mass, core volume and flow.

Don't bother buying this one.

In Part Two of our test we'll look at the ten remaining intercoolers and summarise the results - don't miss it!

Contacts/Thanks

Thank you to Frank Intini of Adelaide's F&M Cylinder Heads (+61 8 8294 2515 or fmheads@ozemail.com.au) for use of his Superflow flow bench; Adelaide Japanese Dismantlers (+61 8 8369 1156 or www.adelaidejap.com.au) for supplying the second-hand import intercoolers and Exhaust Technology for supplying the new aftermarket intercooler and fabrication of the flow bench adapter and tubes (+61 8 8272 7500).

All services and products were provided at no charge.

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