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Issue:
125

Section:
Technical Features

Published:
10 April, 2001

Cooler
Flows

Comparing
the flow capabilities of secondhand Japanese import
intercoolers.

By Michael
Knowling

Japanese-import intercoolers have helped make turbocar modification
extremely affordable. Just a few years ago, the only readily available
approach to charge-air cooling was a fabricated intercooler - often at a
cost of well over $1000. Today, however, imported secondhand cores are
commonly available for less than $300 - an expensive custom or aftermarket
intercooler is no longer a requirement unless you're aiming for a helluva
lot of power.

As you may be aware, there are many different secondhand intercoolers
for sale at Japanese import wreckers - in fact, it isn't uncommon to see
30-or-so unidentified Japanese intercoolers bundled into a single pile.
Indeed, there's plenty of choice - but it's very difficult to identify
which ones are the best. To help answer this, we went along to Adelaide's
Japanese Motorsport and compared fifteen off-the-shelf secondhand
'coolers.

Methods of Comparison

There are two main considerations when selecting an intercooler -
airflow capacity and cooling capacity.

To obtain comparative airflow figures, we employed an inclined
manometer and, as a source of air, a vacuum cleaner (the most powerful
that we had access to). The nozzle of the vacuum cleaner was taped into
one of the intercooler pipes, while the other intercooler pipe was left
open to atmosphere. Our manometer was then tee'd into the vacuum pipe to
measure the pressure drop occurring. The higher the pressure drop, the
more restrictive to flow the intercooler core is. Relative airflow
measurements were taken by reading off markings on the inclined manometer
scale.

Now - as you may have gathered - this technique doesn't give cfm
figures like a proper flowbench (and a flowbench's absolute cfm figures
are often meaningless anyway, given that they are achieved at frequently
less than 1 psi pressure differential! - Ed). The manometer
measurements do, however, give an excellent comparative airflow
guide - meaning that we canaccurately rank the 'coolers from best to worst
in flow. And how sensitive was our measuring system to flow variation? Put
it this way, we could easily see the difference in the flow restriction of
two intercoolers otherwise identical except that one had 48/48mm plumbing,
and the other had 48/40mm connections!

The other important quality of an intercooler - cooling capacity - is
virtually impossible to measure. (Even on a dyno the test conditions do
not represent real world driving, especially in relation to airflow and
engine load variations. Don't believe all you read!) However, a
guide to intercooler cooling capacity can be found by simply
weighing each core. This identifies the mass of material that charge-air
heat can be transferred to. In most road car applications, it's the
heatsink ability of the intercooler that is at least as important as the
ability of the core to exchange heat with the atmosphere. Therefore,
increased mass generally means a greater heatsink ability - it's no
accident that most aftermarket hi-po cores are heavy, even when they're no
bigger than the factory 'un.

The Data

Here's how our fifteen typical Japanese-import used intercoolers
compared...

Toyota 4A-GZE Supercharged

Performance Ranking

Flow: 11th

Mass: =6th

This was the only intercooler out of the test group that is factory
teamed to a supercharged engine - a 1.6 litre four cylinder rated at up to
123kW. The core has a 2.7 kilogram mass and displayed quite a lot of
airflow restriction - up to manometer 900 units. The ID of its plastic
piping is 44 and 48mm. $100 will buy you one of these cores, but why would
you bother?

Subaru Impreza WRX STi (EJ20)

Performance Ranking

Flow: 3rd

Mass: 1st

Ahh, the 206kW Super Sube intercooler. We were impressed by the airflow
through the late-model STi core - which we tested with the factory
(aluminium) Y-pipe still in place. Its big 65mm outlet and 48mm inlet
enabled it to stop our manometer dye at a low restriction of 750 units. At
4.3 kilograms (again, including the Y-pipe) it also had a high mass. Due
to high demand, the price of a secondhand genuine STi intercooler is
around $595. Those dollars make it an expensive proposition - but if you
can find one available cheaply, grab it!

Toyota Supra Twin-Turbo Air/Air (1G-GTE)

Performance Ranking

Flow: =8th

Mass: =6th

The all-aluminium Supra twin-turbo intercooler is probably the most
popular of all Japanese-import 'coolers. Tied to an engine rated at 157kW,
this relatively long (but not very thick) core flowed relatively poorly at
840 units of restriction on our manometer scale. With a 2.7 kilogram mass,
its potential heatsink abilities were also in the lower half of the
field.

Around $200 will buy you one of these, but it's one to steer clear
of.

Toyota Supra Twin-Turbo Water-to-Air (1G-GTE)

Performance Ranking

Flow: =5th

Mass: =4th without water

This is the only water-to-air intercooler of all fifteen tested. Note
that this core was used on the same twin turbo'd 1G engine as the above
intercooler - but it flows a bit better than its air/air cousin. Weighing
3.1 kilos (obviously, including the core's outer sleeve but not the
all-important water) this core breathes through twin 29mm inlets and a
56mm outlet and drew our blue die up to the 800 units of restriction. When
filled with water, the heatsink ability of this core (as with all
water/air heat exchangers) would be very good. $100 will buy you one of
these in the photographed condition (but you will also need a pump and a
heat exchanger to complete the water-to-air system).

Daihatsu Mira TR-XX Turbo

Performance Ranking

Flow: 13th

Mass: 10th

The diminutive Daihatsu intercooler is designed to flow enough air to
generate a factory power output of only 47kW - and it showed. With 34 and
36mm inlet and outlet pipes, the aluminium end-tanked little intercooler
pushed the manometer to the highest restriction reading of the day - 1300
manometer units! This device weighs 1.1kg and will lighten your pocket by
around $50, but we can't see why you'd want this on any car.

Toyota Celica GT4 Turbo (3S-GTE)

Performance Ranking

Flow: =5th

Mass: =4th

Like the Supra air-to-air intercooler, this unit is quite thin - but
that's no surprise as it is designed as a top-mount to fit under the
bonnet of the Celica GT4. Rated for use on a 153kW engine, the GT4 core
weighed in at 3.1 kilograms and drew only 800 units of restriction. It
connects into 45mm ID aluminium pipes. Expect to pay around $200 for this
pretty good intercooler.

Nissan R31 Skyline (RB20DET)

Performance Ranking

Flow: 11th

Mass: 8th

The R31 Skyline GTS uses a 133/141kW version of the RB20 twin-cam
turbo. The intercooler that's used is tucked into the guard - hence the
compact, boxy dimensions of this core. With plastic tanks and 45mm piping,
this device caused a high 870 unit pressure drop and its weight is 2.1
kilograms - towards the bottom of the field in both aspects. Expect to pay
around $150 for an intercooler such as this, but don't get too
enthusiastic about buying it when you find one.

Toyota Soarer Twin-Turbo (1JZ-GTE)

Performance Ranking

Flow: 6th

Mass: =4th

The intercooler fitted to the 206kW 2.5 litre twin-turbo Soarer is an
interesting bit of gear. Very thick but with relatively little frontal
area, it has fat 63mm pipes leading in and out. Extra finely spaced
turbulator fins (clogged with oil on our example) were clearly visible
inside the core. The oil probably contributed to this device's relatively
poor airflow rating (given its volume) - 820 units of restriction were
seen on the manometer. It weighs 3.1kg. $250 will buy you one of these,
which, when cleaned out, looks to have good potential.

Nissan CA18DET Turbo

Performance Ranking

Flow: 9th

Mass: 7th

The ultimate guise of the CA-series motor was the 130kW DOHC, 16-valve
CA18 turbo - and this is its intercooler. Minus its heavy gauge plumbing
(45mm diameter in and out) this core tipped the scales at only 2.5kg and
in terms of airflow, it pushed a high 850 units of restriction on our
inclined manometer. This poor 'cooler retails for around $120.

Kei Class Intercooler - Long and Skinny

Performance Ranking

Flow: 12th

Mass: 9th

The origin of this long and skinny intercooler is unknown - but it's
quite possibly from another 660cc Kei-classer. With 45mm internal diameter
inlet and outlet pipes it flowed quite poorly, displacing 910 units of
restriction. Its weight was approximately 1.5kg. Around $100 will buy you
this cutie - but you'd never want to use it except as a paperweight.

Nissan Pulsar GTiR (SR20DET)

Performance Ranking

Flow: 7th

Mass: 3rd

The ultimate SR20 - the 164kW version as fitted to the Pulsar GTiR -
uses a large area top-mount intercooler. Made completely from aluminium
(including the end-tanks) it tips the scales at 3.4 kilograms. The 52 and
55mm ID plumbing also helps it to flow satisfactorily - drawing up to 830
units of restriction on our test. A GTiR core costs around $500 -
overpriced considering its performance in this company.

Mazda Series 6 RX7 Twin-Turbo (13B)

Performance Ranking

Flow: 2nd

Mass: 5th

The 190kW Series 6 RX7 uses a single air-to-air intercooler to cool the
charge-air from its sequential snails. This core uses a 63mm inlet and
outlet pipe on its plastic end-tanks and was enough to keep the blue dye
down to only 730 units of restriction. Very high-flowing indeed, although
its heat sink capacity was further down the field at around 3.0kg.

Two hundred dollars will get you a S6 intercooler - a good buy.

Mazda Series 4 RX7 Turbo (13B)

Performance Ranking

Flow: 4th

Mass: =6th

The 150kW Series 4 RX7's intercooler is also another capable performer.
With 48mm ID plumbing and nice flowing end-tanks, this 'cooler moved the
manometer fluid up to only 760 units of restriction. It weighed 2.7
kilograms. The cost for a S4 intercooler is 200 dollars - another good
buy.

Mazda Series 5 RX7 (13B)

Performance Ranking

Flow: =5th

Mass: =6th

The Series 5 RX7 intercooler is very similar to the S4's. The biggest
difference is one significantly smaller diameter pipe. Where the Series 4
used 48mm plumbing on both sides of the core, this version used a 48 and
40mm piping. Other than that it looks identical. The S5 core was measured
as having 800 units of restriction and weighed the same as the S4
intercooler (2.7kg). Again expect to pay around $200, but pick the above
intercooler in preference.

Trust Series 4 RX7 Turbo (13B)

Performance Ranking

Flow: 1st

Mass: 2nd

We threw in this secondhand aftermarket core just out of curiosity -
and, boy, did it flow. Despite having modest 51 and 53mm plumbing, this
monster displaced only 650 units of restriction. Its mass was also quite
good for heatsinking at 4 kilograms.

Being Japanese brand name, though, expect to pay up to $695 for this
used core - ouch.

Assessing the Results

In terms of outright airflow, the aftermarket Trust core convincingly
proved to be the best in this group of fifteen. The best heatsink award
goes to the Subaru STi intercooler (even without the added weight of its
aluminium Y-pipe). But - most importantly - the overall winner must surely
be the Mazda Series 4 and 6 RX7 intercoolers. Costing a mere $200 each,
these flowed very well and had adequate heat-sinking abilities. On the
same value-for-money basis, other honourable mentions are the Celica GT4
and the RX7 Series 5 intercoolers.

Contact:

Japanese Motorsport
+61 8 8260 6919

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