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Intercooler Enhancement

Improving intercooler performance for minimal cost and effort.

By Michael Knowling

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At a glance...

  • Improving intercooler performance for under AUD$20
  • Minimal effort
  • Noticeable results
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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 effort?

Well, if the answer is “yes” on both counts, read on!

Testing the Demo Car...

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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 patterns...

Surprisingly, the standard intercooler maintains near-ambient intake temps in slow moving traffic. There are no major heat-soak effects in normal light-throttle driving.

But the story is quite different when you stop the car after driving on boost.

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 bumper.

And what about intercooler performance while on boost?

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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 identify.

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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 intercooler.

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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 Selection

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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.

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Using a pair of scissors, we cut an appropriate length foam strip from our irregularly shaped off-cut.

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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.

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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 passage...

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.

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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 intercooler.

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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 black.

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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.

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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+ aftermarket intercooler.

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.

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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 markedly reduced.

Obviously these are relatively small gains but, hey, for less than AUD$20 and minimal effort, it’s gotta be worthwhile!

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