Rex Intercooler Overload

This article was first published in 2003.

Take a glance at the front of a goggle-eyed Impreza WRX and you'll see that plenty have been fitted with front-mount intercoolers. But what you probably don't realise is that most of these cars will be in one of two categories - (a) their brand new shiny intercoolers are actually pretty bloody small, or (b) the front chassis rails are simply flapping around in the breeze.

The WRX intercooler fitment shown here is different: not only does it have a the huge Blitz cooler kit in place, but the front-end metalwork that had to endure the angle grinder has been boxed and welded, the chassis rails joined by heavy-wall tube.

So hang on while we show you what's involved in fitting about the biggest possible 'cooler to your MY02 WRX... as you'll see, it's no job for the fainthearted! The work was carried out at ChipTorque's workshop in Queensland, Australia, with major input also from Hinterland Exhausts and Hinterland Smash Repairs. From start to finish the job took two full days... two days?!

Yep, as we said, it's not a quick and easy thing to do....

The Bits

The Blitz kit is extensive and well made. The 'cooler core - while being a tube and fin rather than the heavier bar and plate design - weighs in at 6kg, much heavier than the 3.5kg standard underbonnet intercooler. (The heavier it is, generally the better it is at heatsinking - a primary function of intercoolers on road cars.)

Inside the Blitz intercooler tubes are turbolator fins, which create turbulence and so promote better mixing of the air, bringing more air in contact with the alloy. However this causes a greater pressure drop across the core than would occur if they weren't there - you win some, you lose some.

The pipe work is quality mandrel-bent alloy (both light and with a constant pipe diameter through the bends) and silicone hoses are used to join the many bits. The fitting of the kit also requires the use of a pod filter, as a pipe passes through the spot where the airbox once sat. Note the removable directional sticker on the pipe - unfortunately, one section of pipe has it facing the wrong way!

So what's being replaced? As we're sure you all know, WRX models have the standard intercooler mounted under the bonnet over the top of the gearbox. This gives a short turbo > throttle body route but also allows the 'cooler to get heat soaked when the car is stopped - even just at traffic lights. The core itself is fine; it's just that its position isn't so great. (And what about mounting this core at the front of the car? It can be done, but the plumbing connections on the core require huge reworking to get a good job.)

Disassembly

The first step that Nick Stathis undertook was to remove the airbox...

...followed by the top-mount intercooler. That's pretty much it for removals (and modifications) in the engine bay - most of the work is around at the front of the car.

With the car up on the hoist to allow easy access underneath (one of the new 'cooler pipes passes under the engine bay) it was easy to access the guard liners and drop their fronts. (The liners don't need to come right out - just enough that the front bar can be removed.)

Next the plastic undertray was removed, along with the headlights and their associated trim panels...

...and then the bumper cover could be unclipped and carefully drawn away from the body. This is a two person job - not because it's heavy (it's a featherweight piece of plastic) but because it's easy to scratch its paintwork or the front guards. Note the piece of expanded polystyrene foam which normally nestles behind the plastic cover - we'll come back to this later.

Revealed behind the plastic bumper cover is this sturdy box section, which bolts both sides to the longitudinal chassis rails that pass through the engine bay. The large square opening at the right (matched by one at the other end) is for the foglight.

The metalwork unbolts and can then be pulled off the front of the car. Importantly, the Japanese domestic model doesn't run the box section - in its place, a small diameter round tube connects the chassis rails together.

Cutting Metal

Room for the big core is tight - just how tight you'll see in a minute. Part of the space creation scheme is to turn the horns around so that they face the radiator - there's room for their brackets to be bent a little so that they aren't actually touching the radiator core.

Aah, we're at the cutting stage - but just the very beginning of that process. Small lugs at the bottom of the radiator support panel need to be removed so that the intercooler core can rest flush up against this panel. Nick used a plasma cutter to do this job.

The new 'cooler can then be offered up to the radiator. It's held in place by three (supplied) brackets, each of which uses a factory bolt. All looks easy, huh? But take a look at the chassis rail that can be seen on the right - and remember the bumper sheetmetal that's not here...

Room also needs to be made for the substantial plumbing that connects either side to the bottom of the core. Again the plasma cutter was used to trim away this sheetmetal. However, bigger guns needed to be brought to bear on the main guts of the bar.

Hinterland Exhausts were called upon to apply their big angle-grinder, cutting through the bar either side of where the 'cooler would sit. Effectively, the core takes up the space where this box section previously was.

With the box section gone, the core fits into place - nearly, anyway - with the front sheetmetal back on the car. However, clearances are so tight that even the upper bumper cover mounting strip (the only bit of metal left connecting the two bumper boxes) needs to be trimmed.

New Metal

Losing all of the structural integrity of the front connecting sheetmetal is obviously not on, so a leaf was taken out of the Japanese model's book. Instead of using a round steel tube, a 3.5mm wall-thickness 50 x 25mm rectangular section tube was used. Rob Coutts of Hinterland Smash was called in to perform the sizing and welding.

However, before the new tube could be MIG'd into place, the sections either side were strengthened to take the more concentrated loads. Two sheet metal plates were cut out with the plasma cutter and then...

...were welded into place, boxing off the sections either side and giving them much better rigidity. This work was done off the car.

The assembly was then bolted back onto the WRX and then new tube clamped into position. Rob used a level to make sure that it was at the right angle (and he checked that the car was level first!).

The heavy gauge tube was then welded into place. The new brace goes where previously the expanded polystyrene fitted behind the bumper cover, and so with the cover in place it is nearly completely hidden. The whole assembly unbolts, so the intercooler is still easily able to be removed.

Painted black the front metalwork assembly ends up looking like this. While in torsion the new metalwork probably doesn't have the same strength as the original, in compression and bending it is probably superior - and certainly could be expected to be as good as the Japanese domestic model.

The Plumbing

Out of the turbo the plumbing first expands in size then dives down past the gearbox to work its way forward under the car. Nick's looking pretty hard at this piece of aluminium pipe because it's here where he decided to mount the new blow-off valve, a plumb-back (ie recirculating) Turbosmart design.

Hinterland Exhausts did the welding, adding a short length of tube onto which the Turbosmart valve directly fits (it's then held in place with grubscrews).

Despite appearances, the pipe under the car doesn't cause any ground clearance issues - in fact the plastic undertray fits right back on without needing to be cut.

However, because this kit is designed not for a standard WRX's 5-speed gearbox but for the STi's 6-speed, a new bracket needs to be made to mount one of the plumbing bends. As can be seen here, a simple straight length of thick steel strip does the job.

The pipe from the turbo ducks back from under the car and around the front corner, passing through the opening in the bumper end-box that was earlier made with the plasma cutter. The kit's plumbing initially looks like it has too many sections but longer lengths would be impossible to fit.

The fitting of the pipe on other side of the 'cooler - the feed to the throttle body - is a bit more complex. A hole needs to be cut out of the inner guard to allow it to pass through (or more accurately, two holes already present need to be connected and enlarged to form an oval-shaped opening) and then....

...the new pipe can be placed into location. This one's a long 'un, and it's also the one with the directional sticker on backwards.... all of which caused a few moments of confusion!

The pod filter could then be installed. Because this model WRX integrates the airflow meter into the airbox, a new alloy casting is used - with the airflow meter guts being swapped over. A Blitz filter and adaptor have been used here.

With all the plumbing in place (yes, those pipes sure are big!), it's time to head for the home straight - getting the bumper cover back on. As you might expect, that involves cutting away quite a lot of plastic to give the necessary clearances.

The Cover

First up the foglights need to come out - their rear extremities fit right where the intercooler plumbing now goes. There are two ways of replacing them - either polish the pipes now visible and let them show through proudly, or use STi foglight covers.

After marking out the bumper cover, Nick used an air-powered hacksaw to make the initial cut. You can't put any of the plastic back so it's a case of taking it real easy on the first incision...

A neat finish was achieved by using a small powered sanding belt. Care needs to be taken that the cutting/sanding speed isn't too high or a globuled, melted look will result.

With the hindering plastic removed, the cover could be offered up to the intercooler - and then taken off again for the final finicky cuts to be made.

With the plastic bumper cover back in place you'll need to get down on your hands and knees to see the new behind-bumper steel tube - here it can be just seen above the intercooler.

Headlights back in, grille and bumper in place, this is what the job looks like - just waiting on those foglight covers.

ChipTorque's Stef places into a box the items that the owner will get back - airbox, foglights and the original intercooler - and the job's finished.

Conclusion

The intercooler is huge (including end tanks, it's all of 830 x 266 x 70mm), and the plumbing going to and from it is large with gradual and smooth bends. But looking at the extent of the changes that need to be made to the car, if you later wanted to return it to standard you'd need to buy new bumper bits and have them painted to suit. It's also certainly not a kit to fit if you don't want to go the extra distance and rigidly connect the two chassis rails back together.

But if you want to be able to run a heap of reliable boost and really shed that charge-air heat, this size of 'cooler is one undoubted big plus....

www.chiptorque.com.au

Hinterland Performance Exhausts
07 5596 2338

Hinterland Smash Repairs
07 5527 3344

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