The World's Biggest Intercooler Comparison - Part Two

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 full of bargain intercoolers.

The big question is which of these intercoolers are the best in terms of flow and thermal efficiency? In the second part of this two-part series, we look at the remaining ten (out of twenty-five) intercoolers we have on test and summarise the results.

Test Results (Continued)

Nissan R31 Skyline GT RB20DET Guard-Mount Air-to-Air Intercooler

Flow - Direction A (air exiting right-angled pipe) 181.2 cfm (21^st overall)

Direction B (air entering right-angled pipe) 162.9 cfm

Mass - 2.3kg (13th overall)

Core Measurements - 18.5 x 22.2 x 5cm = 2054cm3 (23^rd overall)

Fitted to the Japanese market R31 Skyline 2.0-litre six-cylinder turbo, this front-mount intercooler is typical of most compact Nissan 'coolers. It uses plastic end-tanks, a relatively small core and looks quite cheaply manufactured. Thermal mass is reasonable (partly thanks to a steel mounting bracket we couldn't remove) but its poor flow means this is an intercooler to stay away from.

You could use it in applications up to about 150kW if you had to.

Nissan Skyline R31 GT RB20DET Top-Mount Air-to-Air Intercooler

Flow - Direction A (air entering large diameter pipe) 195.6 cfm (16^th overall)

Direction B (air exiting large diameter pipe) 176 cfm

Mass - 1.9kg (equal 20th overall)

Core Measurements - 22.0 x 20.5 x 5.0cm = 2255cm3 (18^th overall)

This is the top-mount intercooler that was offered on some versions of the Japanese R31 Skyline turbo. Similar overall to the guard-mount version, this 'cooler has slightly different end-tanks and larger core dimensions contributing to a better cfm rating than its cousin. Thermal mass isn't up to the guard-mount version, however.

Again, we'd put up with using this intercooler only in applications up to about 150kW.

Nissan S13 Silvia SR20DET Air-to-Air Intercooler

Flow - Direction A and B 185.5 cfm (19^th overall)

Mass - 4.6kg including cast alloy pipes (4^th overall)

Core Measurements - 22.0 x 16.8 x 5.8cm = 2144cm3 (22^nd overall)

This is the very heavily constructed intercooler that's fitted inside the guard of SR20DET Japanese market S13 Silvias. Note that this 'cooler uses dedicated cast aluminium entry and exit pipes that match flanges on the end tanks. As such, we were forced to flow test this intercooler with the pipes attached and we recorded a slightly pessimistic 185.5 cfm figure. On the other hand, the extra weight of those thick aluminium pipes gave the Silvia intercooler an overly generous thermal mass rating. Keep these factors in mind when looking at the graphs further into the article.

Like the R31 intercoolers, we'd try to keep this intercooler out of vehicles making more than about 150kW.

Nissan Pulsar GTi-R SR20DET Air-to-Air Intercooler

Flow - Direction A (air entering large diameter pipe) 236 cfm (8^th overall)

Direction B (air exiting large diameter pipe) 233 cfm

Mass - 4.7kg (3^rd overall)

Core Measurements - 29.5 x 35.0 x 5.8cm = 5989cm3 (4^th overall)

We had high expectations for the Japanese market Nissan Pulsar GTi-R intercooler and it didn't let us down. Factory-fitted to the 162kW version of the SR20DET, this 'cooler offers good airflow together with very large core area and thermal mass. A great pick if you're chasing every last bit of cooling performance.

This is an excellent all-round intercooler we'd be confident using in applications in excess of 200kW.

Toyota GX81-series 1G-GZE/1G-GTE Air-to-Air Intercooler

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

Direction B (air exiting longer pipe) 209 cfm

Mass - 2.2kg (14^th overall)

Core Measurements - 37.5 x 18.0 x 6cm = 4050cm3 (8^th overall)

We're told this particular intercooler is the same as fitted to the 1G supercharged 2.0-litre six and the 1G twin-turbo 2.0-litre six (the 1G-GZE and 1G-GTE respectively). A common choice for conversions in medium power applications, this 'cooler has a generous core volume, average thermal mass and decent airflow.

Not at the top of the medium size intercooler field but certainly worth considering for applications up to about 180kW.

Toyota Supra (JZA70) 2.5-litre Air-to-Air Intercooler

Flow - Direction A (air entering shorter pipe) 265 cfm (5^th overall)

Direction B (air exiting shorter pipe) 252 cfm

Mass - 3.8kg (5^th overall)

Core Measurements - 48.7 x 17.8 x 7.2cm = 6242cm3 (3^rd overall)

Australian-delivered Toyota Supra turbos from the late '80s never came with the option of the 2.5-litre 1JZ twin-turbo, which was available in Japan. The 206kW 1JZ-GTE in the Japanese JZA70 Supra is fitted with the long, skinny all aluminium intercooler seen here. This 'cooler offers a huge core volume and impressive thermal mass along with airflow that's bettered by very few in this test. This really is a great unit.

There's no reason why this intercooler can't be used on engines making considerably in excess of 250kW.

Toyota Soarer (JZZ30) 2.5-litre Air-to-Air Intercooler

Flow - Direction A (air entering angled pipe) 268.5 cfm (4^th overall)

Direction B (air exiting angled pipe) 262 cfm

Mass - 3.15kg (8^th overall)

Core Measurements - 23.5 x 20.5 x 10cm = 4818cm3 (7^th overall)

The same 206kW 1JZ twin-turbo motor used in the JZA70 Supra was also dropped into the late model Soarer body. In the Soarer, however, limited space meant a 'box style' intercooler had to be squeezed into the left-hand guard. Using lightweight plastic end-tanks its thermal mass and core volume aren't as high as the 1JZ Supra's, but it still rates well in absolute terms. The Soarer box intercooler is also more restrictive than the 1JZ Supra's, but only by a slight margin - this is still a very good intercooler.

Again, this 'cooler is at home on engines making over 250kW. Add a water spray in extreme cases.

Toyota AE92 Levin 4A-GZE Air-to-Air Intercooler

Flow - Direction A (air entering plastic pipe) 207 cfm (14^th overall)

Direction B (air exiting plastic pipe) 187.6 cfm

Mass - 2.1kg including exit plastic pipe (equal 15^th overall)

Core Measurements - 18.7 x 22.5 x 6.0cm = 2525cm3 (16^th overall)

The 4A-GZE intercooler is the only example on test that's used on a factory supercharged engine. The blown 4A 1.6-litre four-cylinder makes 123kW in standard form and its 'cooler rates average in heat exchange and flow performance. No need to search high and low in desperation to find this one. Note that the plastic pipe remained in place for flow testing, meaning its cfm figure is slightly handicapped.

A decent all-round intercooler for engines producing up to around 140kW.

Volvo Front-Mount Air-to-Air Intercooler

Flow - Direction A and B 200 cfm (15^th overall)

Mass - 2.5kg (11^th overall)

Core Measurements - 45.0 x 41.0 x 3cm = 5535cm3 (5^th overall)

This impressive looking intercooler has been pulled from a turbocharged Volvo - probably a 700-series. Its 5th position core volume comes as no surprise, but its thermal mass is let down by thin plastic end-tanks and a very thin core. That thin core also let it down on the flow bench where it ranked in the lower half of the field.

Its huge frontal area means this might be a good intercooler for sustained high-speed use (such as on a racetrack). Its poor flow, however, means it's inappropriate on engines making more than about 150kW.

Subaru Version 2 (MY94-96) STi Air-to-Air Intercooler

Flow - Direction A only (air entering bolt-on pipe) 224.2 cfm with bolt-on pipe attached (10^th overall)

Mass - 2.8kg (10^th overall)

Core Measurements - 40 x 11.5 x 6.2cm = 2852cm3 (15^th overall)

The Version 2 STi intercooler is very similar to the unit fitted to the Australian Version 2 (1994 - 1996) WRX, the only important differences being a slightly different end-tank and a high-flow entry pipe. Even with its separate high-flow entry pipe attached, this intercooler flowed well - a top 10 finisher. Its thermal mass and core volume fall in the middle of the field.

A decent 'cooler for use on engines up to about 200kW - especially if you add a water spray etc.

New Aftermarket Front-Mount

Flow - Direction A and B 372 cfm (1^st overall)

Mass - 7.3kg (1^st overall)

Core Measurements - 29.4 x 58.5 x 7.5cm = 12899cm3 (1^st overall)

This is the only brand new Japanese aftermarket intercooler on test - it's a yardstick to compare the OE cores. As you can see, this is a positively huge intercooler that ranks Number One in core volume, mass and flow. Note that it outflows the best OE intercooler (the Series 6 RX-7) by a relatively small 20 percent, but its heat exchange potential is in another league.

This intercooler could be used in pretty well any high-powered turbo or supercharged streetcar - assuming it can be made to fit!

The Results At a Glance

As mentioned, the new aftermarket core beat the flow of its nearest rival (the Series 6 RX-7) by 20 percent. The Series 6 core features large diameter hose connections but - to prove that's not the only external indicator to flow - the Volvo/Saab intercooler pipes are equally large and the unit flowed miserably! The intercoolers fitted to vehicles near the Japanese regulated 206kW output flowed very well. Just to put a slant on that, though, the little Familia GTX and Charade GT-ti intercoolers were right up there with the best of them!

All this just goes to prove you can't assess the flow of an intercooler just by looking. Flow bench testing really is mandatory.

This graph clearly shows the superior mass of the aftermarket intercooler - the big bar-and-plate core construction is much heavier than the factory tube-and-fin cores.

Working back to OE intercoolers, the light truck intercooler rated second best in thermal mass but probably largely due to its heavy cast end tanks (rather than the mass of its heat exchange core). The Pulsar GTi-R intercooler was the clear winner in thermal mass of passenger car cores and the Silvia intercooler also looks impressive on the graph - note, though, the quoted mass includes the cast alloy entry and exit pipes so this figure is quite optimistic.

The big power Toyota engines have good 'cooler mass with the Soarer and 1JZ units rating in the top few, as does the large Japanese-spec VR4 'cooler. The Isuzu Piazza intercooler also has a very good thermal mass, aided by its thick end-tanks.

The surprise disappointments in the thermal mass stakes include the Series 6 RX-7 intercooler. The Cappuccino intercooler's thermal mass is hardly a surprise...

And here is the second indicator to the intercoolers' heat exchange performance - the volume of their core section.

Again, the aftermarket intercooler and the truck unit are the best, but the Supra 1JZ and GTi-R cores aren't far behind. These would be great in a front-mount race application. The Saab/Volvo core also put in a very impressive core volume but - as seen above - its poor thermal mass largely offsets any positive. The Japanese market VR4 intercooler is the next best, beating the Soarer 1JZ unit and all of the Mazda rotary intercoolers. With the exception of the baby Cappuccino intercooler, most of the remaining intercooler core volumes range between 2000 and 3000 cm3.

Summary

Obviously, we have a clear winner across the board - the aftermarket front-mount intercooler tops the field in flow, thermal mass and core volume. If you're prepared to spend the extra money, you can certainly get a very good 'cooler.

But what about the cheaper second-hand import intercoolers?

The top three finishers in the OE intercooler category are the skinny 1JZ intercooler (5^th for flow, 3^rd for core volume and 5^th for mass), Pulsar GTi-R intercooler (8^th for flow, 4^th for core volume and 3^rd for mass) and the Soarer 1JZ intercooler (4^th for flow, 7^th for core volume and 8^th for mass).

The Mazda Cosmo intercooler (3^rd for flow, 9^th for core volume and 8^th for mass) also performed exceptionally well overall, while the Series 6 RX-7 unit (2^nd in flow, 19^th in core volume and equal 17^th for mass) looks great if you augment it with a fan and water spray. The Series 6 intercooler has truly awesome flow but needs all the help it can get in the heat exchange department.

The top performer in the smaller category is the Isuzu Piazza intercooler (9^th in flow, 12^th in core volume and 7^th in mass), followed by the GX81-series 1G (equal 11^th for flow, 8^th for core volume and 14^th for mass) and the Mazda Series 5 RX-7 unit (7^th for flow, equal 13^th for core volume and equal 17^th in mass).

We were surprised to see the humble Familia GTX intercooler perform as well as it did on the flow bench - give it a fan and water spray (as we've covered in previous articles) and you've got a very effective little unit. The same goes for the 3-cylinder Daihatsu GT-ti intercooler, which flowed amazingly well for its size.

There are also a few shocker performances worth mentioning here.

The Mitsubishi Lancer GSR intercooler flowed abysmally (only the tiny Suzuki Cappuccino intercooler was more restrictive), the Japanese spec VR4 intercooler was extremely restrictive and the impressive looking Saab/Volvo intercooler was out-flowed by more than half of the field. Strangely enough, the much sought after Familia GTR intercooler was also out-flowed by the everyday Familia GTX unit - it appears Mazda decided to chase improved thermal properties for the GT-R rather than prioritising flow.

As we've proven, things are often not as they seem when picking an intercooler!

Prices? The second-hand intercoolers on test were all obtained from Adelaide Japanese Dismantlers. The price of these intercoolers constantly varies depending on supply and demand but, at the time of writing, these are the prices (quoted in Australian dollars)... Mazda B6 $195 Mazda Familia GTX $175 Mazda GTR $275 Mazda Series 4 RX7 $195 Mazda Series 5 RX7 $195 Mazda Series 6 RX7 $275 Mazda Cosmo 20B $250 Mazda 626/MX6 Turbo $450 Diesel Truck $350 Mitsubishi JDM VR4 $500 Mitsubishi 1.8 GSR $125 Daihatsu GT-ti $135 Isuzu Piazza $150 Suzuki Cappuccino $50 Nissan R31 (guard-mount) $175 Nissan R31 (top-mount) $135 Nissan Silvia $250 Nissan GTi-R $500 Toyota 1G $320 Toyota JZA70 Supra $450 Toyota JZZ30 Soarer $350 Toyota AE92 Levin $195 Volvo/Saab $275 Subaru Version 2 STi $275 Be wary, though, these prices are subject to ongoing variation. The new aftermarket intercooler on test retails for $850 (plus fitting) through Adelaide's Exhaust Technology. However, for a limited time, AutoSpeed readers can pick it up for the special price of $800.

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 http://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.