This article was first published in 2005.
Do you own a turbo car with a standard front-mount air-to-air intercooler?
Want to improve intercooler performance for about AUD$20 and with minimal
Well, if the answer is “yes” on both counts, read on!
Testing the Demo Car...
The demo car for this article is an Australian-delivered Mitsubishi Galant
VR4. The VR4 employs a typical front-mount intercooler arrangement – its
air-to-air core is mounted in the nosecone ahead of the air conditioning
evaporator and coolant radiator. Oncoming airflow makes its way to the core
through a passage in the bumper bar. Pretty simple.
With a trusty LCD temperature probe fitted in the intercooler outlet pipe, we
drove the VR4 in a variety of conditions - and recognised some interesting
Surprisingly, the standard intercooler maintains near-ambient intake temps in
slow moving traffic. There are no major heat-soak effects in normal
But the story is quite different when you stop the car after driving on
Intense heat from the area of the turbocharger makes its way to the VR4
intercooler and causes a gradual charge-air temperature rise. Stopping the car
after a couple of standing start sprints, we saw intake air temperature creep up
to 43 degrees Celsius (with an ambient temperature of 25 degrees). This
charge-air heat lingers until there’s a steady flow of cooling air through the
And what about intercooler performance while on boost?
Well, it’s obvious the Australian-spec VR4 intercooler is quite inefficient.
Its small size and lack of internal cooling fins allow intake air temperature to
rise about 10 degrees Celsius when barely pulling away from traffic... At
wide-open throttle from 1000 to 7000 rpm in second gear, we saw intake air
temperature rocket from 29 to 41 degrees Celsius. Again, ambient temperature was
around 25 degrees Celsius.
The heat-exchange performance of the VR4 intercooler is also poor when
driving on the open road – the rush of incoming air fails to cool the
intercooler as quickly as we expected.
Identifying the Problems
The problem of turbocharger heat affecting the intercooler was easy to
After removing the vehicle’s grille, we accelerated hard from a couple of
standing starts and pulled to the side of the road. Reaching a hand down near
the intercooler, a turbulent mix of hot air could be felt swirling around behind
the core whenever the thermo fan was operating. It was obvious the thermo fan
was blowing super-heated air from the turbocharger through a large gap alongside
the radiator to the area of the intercooler.
This gap had to be sealed.
Next, we looked at improving the overall heat-exchange performance of the
The disappointing heat-exchange performance on the open road hinted that
cooling airflow wasn’t effectively acting on the intercooler core. This was
confirmed when we looked at the front face of the core – there’s a gap of around
3cm between the core and the airflow passage in the bumper, which allows cooling
air to flow around the intercooler
rather than through it.
The obvious remedy was to seal the front face of the intercooler to the
bumper’s airflow passage.
Fixing the Problems
The gap down the side of the radiator was sealed using foam strip. We chose
foam because it’s cheap, easily workable, lightweight, provides excellent
sealing and can be painted black for stealth installation.
Foam off-cuts are widely available in 3 different densities – it’s generally
best to go for the highest density foam to achieve optimal sealing properties.
We bought medium density foam knowing it would be heavily compressed when
installed in the vehicle. (Heavily compressing the foam between two surfaces
gives enhanced sealing).
The cost for our foam off-cut was under AUD$10.
Using a pair of scissors, we cut an appropriate length foam strip from our
irregularly shaped off-cut.
Next, the foam strip was trial fitted in the gap between the radiator and
body. The foam is sandwiched tightly between each surface for maximum sealing.
Once we were happy with the fitment of the foam strip, we removed it from the
car and spray painted it black to give a stealth installation. Foam absorbs a
lot of paint so you’ll need to apply a few coats for a good finish.
This photo shows the foam strip being installed in its final guise. Liquid
adhesive can be used to secure the foam in place, but we didn’t bother - there’s
no way our heavily compressed strip of foam is going anywhere by itself!
Now for the job of sealing the intercooler to the bumper bar airflow
For this task we employed a combination of foam and rubber strips - foam
strips were used to seal each side of the intercooler while rubber strips were
used to seal the top and bottom edge.
We started by cutting another pair of foam strips and test fitting them in
the vehicle. In this case, the foam strips are sandwiched vertically between the
metal bumper structure and the intercooler end-tanks. Note that the foam strips
should not block cooling airflow to the all-important core section of the
Our vertical foam strips were then trimmed in length to provide a slight
overhang at the top and bottom of the core. These overhangs will be later
compressed against the rubber sealing strips that will be fitted along the top
and bottom edges of the intercooler. At this point we painted the foam strips
With the foam strips painted and reinstalled between the intercooler and
bumper, we turned our attention to sealing the top and bottom edges of the
intercooler using a pair of rubber strips. Why use rubber strip, you ask? Well,
in the case of the VR4, the top and bottom edges of the intercooler align
closely with the top and bottom edges of the metal bumper structure – this made
it easy to lay flat strips of rubber to form a seal. Total cost for the rubber
strip was AUD$5.
With a pair of rubber strips cut to the width of the intercooler, each was
glued directly to the core and metal bumper structure. We used Selleys Liquid
Nails to adhere the rubber strip – and there have been no problems.
Note that the overhangs we left in our vertical foam strips provide excellent
sealing against the rubber strips. This ensures no cooling air can escape
through the corners.
And that’s it – we’re done!
We could tell you that we achieved
the same sort of heat-exchange performance you’d expect from an AUD$500+
But we’d be lying.
By sealing the intercooler core to the bumper bar passage we recorded a
small but noticeable reduction in charge-air temperature. We’re now seeing
around 36 degrees Celsius after a WOT second gear run under 25 degrees Celsius
conditions – an improvement of around 5 degrees Celsius.
However, the most noticeable improvement has come from sealing the gap
alongside the radiator. Heat from the area of the turbocharger now has
absolutely no affect on the intercooler and, as a result, the car feels less
‘soggy’ on take-off after heavy driving. The chance of engine detonation in these conditions is also
Obviously these are relatively small gains but, hey, for less than AUD$20 and
minimal effort, it’s gotta be