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Cooler Runnings

Slashing the charge-air temps of a Nissan 180SX turbo...

By Michael Knowling

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This article was first published in 2002.

The stockie intercooler fitted to a turbocar is usually fairly average. When you force a few extra psi boost through the standard unit, its heat-exchange and airflow performance are often quite severely reduced. Not surprisingly, therefore, an upgrade aftermarket intercooler is required in all truly serious power-ups. Furthermore, an upgrade intercooler should be an even higher priority for 'grey' Japanese-import vehicles; running an engine designed for 100RON fuel on only 98RON (or less) is a formula for engine-destroying detonation. Keeping a lid on intake air temps is an effective way to combat detonation.

In this story we look into the gains of fitting an aftermarket intercooler on a lightly tuned Nissan 180SX Turbo...

The Demo Car

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This particular SR20DET 5-speed 180SX arrived at Adelaide's RPM Performance Centre equipped with just a HKS pod air filter and a 3-inch turbo-back exhaust system. On the rollers of RPM's Dyno Dynamics chassis dyno the car produced a reasonably repeatable 138kW at the back wheels.

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The 138kW peak power figure was achieved with absolutely no boost mods and with a maximum manifold pressure of 9 psi. Oh, and - on the dyno - we measured the intake air temperature immediately before the throttle and saw a maximum 41.8 degrees Celsius (with an ambient temperature of around 20 degrees Celsius).

Fitting the New 'Cooler

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The front-mount intercooler kit being fitted here suits SR20DET powered S13 180SXs and Silvias and is a development of RPM Performance Centre (also being sold by For AUD$1895 (supply only) you receive a Garrett bar-and-plate core with mounts and all necessary plumbing and hoses. The new core measures some 450mm x 305 x 90mm and contains dense offset turbulators for maximum cooling efficiency. Tim from RPM tells us he's used this core on a full-house CA18DET making 270kW at the wheels, so it's obviously quite capable.

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The first task is to remove all of the factory intercooler pipes found between the standard intercooler and the throttle, plus the pipe that passes through the guard between the turbo and 'cooler. Oh, and don't forget to stuff a rag inside the open pipes - this prevents foreign particles getting inside the engine.

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Next, the front of the car needs to be jacked up and secured on chassis stands. The guard liner retainers are then removed, which allows access to undo the bolts securing the bumper to the body. Once the bumper bolts and indicator wiring connectors are removed, the entire front bumper assembly can be slid out.

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Now - with much easier frontal access - the standard intercooler, blow-off valve and entry/exit pipe assembly can be removed from the vehicle. As seen here, the factory 180SX intercooler is particularly small, measuring just 170 x 222 x 60mm. Its inlet and outlet fittings have a 47mm internal diameter.

The replacement intercooler gobbles pretty well the entire nose cone cavity. To support the 'cooler's weight, a metal mounting strip is attached to a pair of threaded fittings welded onto the top and bottom of the core - these connect to the vertical support for the bonnet latch and the lower radiator support panel respectively.

Once the big 'cooler is mounted, it's time to hook up the plumbing.

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Interestingly, the RPM kit retains the first section of factory plumbing out of the turbo compressor, but replaces the pipe into the 'cooler and from the 'cooler into the engine. The pipe leading into the 'cooler (and the 'cooler fittings themselves) are normally 54mm ID, but - in this particular kit - they were the standard 47mm diameter. Note that all of the pipes have a rolled lip to prevent hoses popping off under high boost.

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A 35mm ID fitting is welded on the side of the intercooler entry pipe, which allows fitment of either the original or aftermarket blow-off valve. In this instance, the original valve was retained and connected back to the pre-turbo induction pipe using the OE piping. This is widely known as a 'plumb-back' arrangement.

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Inevitably, there is some cutting required to install the kit. First, the radiator shroud needs to have a 100mm square section removed from its top half - this allows clearance for the large diameter pipe into the throttle. Second, the front bumper needs to have some material removed. A slice needs to be taken off the under-tray section, while the central air cooling passage has to be cut back to allow the bumper to fit against the new fat 'cooler.

Total installation time is around half a day.

The Results

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With ambient temperatures virtually the same as the 'before' run, we again fired the 180SX up on the chassis dyno and slipped our temperature probe into hose before the throttle body. The results were particularly interesting - running the same 9 psi boost, intake air temperatures were slashed from a high of 41.8 to just 25 degrees Celsius (which was only slightly above ambient temperature). There was little question the new 'cooler was performing magically.

And did it bring a massive power gain? Well, no, not really...

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Despite its considerably lower intake temperatures, the turbo Nissan gave only a minimal power improvement. As seen in this graph, it picked up a reasonable percentage down low but hardly anything up high - power went from 138 to 142kW (a gain of around 3 percent). We can only surmise that the relatively low boost level on this car minimised the potential for any large gains - there weren't the extreme charge-air temps for the new 'cooler to haul down. Interestingly, Tim tell us he's done similar intercooler conversions in the past and seen only small gains; as he went on, however, it's the potential to allow more boost that makes the process worth while. There's no way you'd want to run more than 15 psi through the standard intercooler, because intake air temperatures would go through the roof. This robs power and can lead to detonation.

So, in summary, we've shown that an upgrade intercooler doesn't always release a huge amount of power - certainly not in the case of a lightly tuned 180SX. Instead, think of this $2000-odd investment as an essential step that allows to you safely increase boost pressure and net the biggest gains.

More Boost?

Installing an aftermarket intercooler often sees higher boost pressure felt in the intake manifold - but not in the case of the 180SX...

On the majority of turbocars, the wastegate takes its pressure feed from the compressor outlet. In these instances, any airflow restriction on-route to the engine (such as an intercooler) reduces the boost pressure that reaches the intake manifold. Say, for example, the wastegate is set to deliver 15 psi, a restrictive intercooler may allow only 12 psi to make its way to the manifold. Fitting a less restrictive intercooler may see 14 psi reach the manifold.

Some vehicles - such as the demo Nissan 180SX SR20DET - take their wastegate feed directly from the intake manifold. This means the turbo will work to deliver the same manifold pressure, regardless of the amount of flow restriction before the throttle. That's why - in this case - the 180SX saw 9 psi manifold pressure both before and after the new 'cooler went on.


RPM Performance Centre
+61 8 8277 2266

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