GT-R RACE INTERCOOLER

R & D

Since first showing our Race Intercooler design a number of years ago many similar designs have appeared across the tuning world, but few will have had the level of testing to understand what internal structure works best.

We thought it might be of interest to show what went into creating an innovative design and how the core selection process involved more than just selecting something off the shelf.

Our original intercooler design had proven its worth as a highly effective component, releasing over 30 additional bhp on our LM750 cars, and improving engine longevity.

However, on cars running over 900 bhp our testing revealed that when the turbos were running at full aerobic capacity, heat generation would start to overwhelm the core’s capabilities.

Designing the new intercooler we knew we wanted to keep the original’s easy fitment, maintain airflow to the radiator and ideally reduce the length of pipework in the engine bay.

After careful analysis and several prototypes we were able to remove no less than a metre of pipework from each side of Nissan’s original induction set-up; a first at the time. This removed weight and, more significantly, allowed us to increase the diameter of the pipework and improve throttle response at the same time.

New, high-integrity ‘V-Band’ flanges were incorporated to attach our re-designed, larger dump valves, which are required to cope with the elevated power level.

On evaluating pressure data it was apparent that our original design air filters were becoming restrictive over 900 BHp. Working with our technical partners Pipercross, we moved to a larger trapezoidal element using triple layer foam borrowed from their motorsport programme in the BTCC and WRC. The foam is able to filter considerably more air than before and still remove finer particles than the standard Nissan filters.

Testing Procedure

With the intercooler design complete we chose four intercooler cores and had them fabricated into test units that would all use our revised pipework. We could then swap between them easily with repeatable tests on both dyno and on tarmac.

The four cores chosen were:

• A high-quality core from Asia in bar and plate format
• A core we specified from one of our British aerospace suppliers
• A slim PWR core
• A full depth PWR core

The Asian core is used by some very top-end names including Greddy. It balances sensible price with excellent flow rates, although they are significantly heavier than the others.

The British aerospace supplier core offers superb quality and is some 6kg lighter than the Asian model. The main downside of this core was the cost per unit and the long lead times for these, which require labour intensive internal structures.

Australian specialist PWR are at the forefront of cooling technology at the moment, being used by every BTCC team, the vast majority of F1 cars and practically every British and German Supercar manufacturer. Quality and build integrity are stratospheric, which is naturally reflected in their cost, but we wanted to evaluate the very best to give perspective to our overall choice. As an additional benefit, these cores are also exceptionally light; yet another 3kg over our own original design.

The initial test was performed on an independent rolling road (as our dyno was still in the planning stage at this time). The car used was our 2011 Stage 5 demonstrator, usually running at around 750bhp on V-Power fuel at approximately 1.5 bar. We wanted to ensure that turbo efficiency and tuning were removed from the equation. We therefore reduced boost to just 1.0 bar with less ignition timing. This meant that the car was running in an unstressed state, and that any improvements shown would be down to the intercooler. The original design intercooler was run to act as a baseline, before each new intercooler was added to an engine at the same operating temperature.

For additional comparison, we also performed a series of runs at 1.4 bar, again with reduced timing to remove any inconsistencies. With this higher boost level any intercooler differences could be extrapolated over a higher power range.

We were also measuring the charged air temperatures and pressures before and after the cores for comparison over a number of dyno runs for each core. The intercoolers needed to be able to handle more than just one single power run as heat dissipation is key to their use.

From this initial test we could draw two main conclusions. Firstly that the new pipe routing design and the new larger cores worked brilliantly and secondly that the PWR cores were superb.

The PWR slimline core performed well, but seemed to saturate with heat quite quickly due to its size. It would also lose that heat extremely quickly, but was not up to running the higher power levels.

The larger PWR core carried a significantly higher price point than our specified core but also out-performed the others.

The Asian core performed well for its price point, but it dissipated heat energy slowly and was significantly heavier than the others.

The pressure drop figures made for interesting reading. The Asian Bar and Plate design has very little restriction and had the lowest pressure drop. Its dense construction meant it had very good performance over one power run, but once it had absorbed this initial heat its heavy construction meant it would take longer to cool down.

The lack of restriction was highlighted by the power it produced at 1 bar. At this boost level the turbos are working well within themselves, and therefore the outlet temperatures were lower so the intercooler didn’t need to absorb as much heat.

The large PWR core had the highest pressure drop, although this is relative as all the cores had excellent pressure drop figures. Its clever internal fin design works the air more to remove temperature. This core came into its own as the power increased and its ability to quickly reject heat made it the most consistent performer.

After these initial tests our British core supplier felt they could improve on their performance and would later supply us with two improved cores for testing.

In the mean time we hired a local airfield to perform repeated high speed running. This would show any difficulty with airflow to the radiator behind the core along with confirming heat buildup and ability for heat dissipation.

Dyno Round 2

The airfield testing validated our dyno testing and confirmed that the PWR large core was the outright winner for performance. We were then able to compare this PWR core to the two new cores supplied by our British core manufacturer in a second round of dyno testing.

Our development car had also moved on as it had now begun testing our LM1 4.6 litre Red Top engine so it was the perfect specification to put the intercooler efficiency to a tougher test.

These new cores featured different internal designs, but kept the price and weight at more acceptable levels. Again we fabricated the cores into the same shape intercooler and hired a Hub Dyno facility more suited to higher power testing.

The development car was filled with super unleaded fuel, had the timing reduced slightly and ran at 1.4bar to give a consistent reading for each dyno pull. This netted around 960+bhp at the hubs (not to dissimilar to what we now see at the crank on our Maha dyno).

The PWR core was used to set the base line runs before we installed the British companies MK2 core. This used a more dense internal fin structure and gave us more power in the mid-range than anything we had seen before however this improvement dropped off as revs increased towards the red line. Their MK3 core gave an increase in power throughout the rev range with around a 12bhp power increase over the large PWR core. It also had very good heat rejection capabilities and at a price that would be acceptable. We repeated the testing on the road/runway to confirm we had found our winner.

We’re sure that PWR could have improve their core for this specific application given more time and data, but we all felt the gains would most likely be minor at this point. As much as we like the quality and technology PWR can offer, the work required to gather the necessary data and the projected core price would ultimately be too expensive.

The Finishied Product

After many months of research we finally had an effective solution; an innovatively designed intercooler that shows gains straight away and a core selection that has been carefully tested.

The Litchfield Race Intercooler has gone on to prove its worth in both competition and many high power road applications. A great example of the level we go to produce such an important product.