Discussion on the development of the APS Front Mount Intercooler System
Intercooling for the XR6T is a complex science and often misunderstood issue because the XR6T is different in its requirements to most other turbocharged vehicles. Many of the upgraded intercooler products available on the market to suit the XR6T have been developed using experience gained with small capacity Japanese turbocharged vehicles. Whilst this approach had been successful to varying degrees with small capacity engines, the XR6T is a different kettle of fish altogether. As is evidenced by the current crop of intercoolers available for the XR6T, some actually perform the total task of intercooling with inferior performance to the stock intercooler, others a modest improvement but very few are optimal in their design and performance.
Many XR6T owners have come across to the blue oval from Japanese turbocharged vehicles such as the WRX/STI and 200SX etc. Their experience with these vehicles makes intercooler systems that employ small capacity intercooler design principles seem attractive and sound in engineering. However, in reality these systems are often not optimal and exist either because the people who developed the intercooler system do not understand the requirements of the XR6T or in fact have chosen to offer products that are easy to sell rather than perform in an optimal manner.
In high powered small capacity engines, a relatively large turbocharger (compared to engine capacity) is used to pump a high mass of air into the engine. This results in lazy response regardless of intercooler system type or size because one has at best 2.0L of engine capacity to drive the turbo. The XR6T on the other hand is blessed with more than twice the capacity to drive the turbocharger and produces a great deal more off-boost torque than a small capacity engine.
This leads to a classic example of irrelevant design issues carried over from small capacity Japanese engines to the XR6T. That is, total system volume and duct length, and its affect on an all-encompassing term response. Duct length has for a long time been confused with turbocharger lag. When one considers the rate at which the XR6T engine consumes air at different power levels, ducting length and its affect on response becomes totally irrelevant to the driver as he punches on the throttle. For example, a metre of 76mm ducting results in .063 sec interval at 100hp, through to 0.015 sec interval at 400hp. This is at a level that that is well below human sense thresholds.
But back to the real issues of intercooling on the XR6T
In a nutshell, the role of an intercooler system on the XR6T is to route hot charge air from the turbocharger and deliver the greatest possible charge air temperature reduction with the lowest possible pressure loss to the inlet manifold - at the rated flow of the turbocharger. To further complicate the issue, the total intercooler system forms a key part of the boost control strategy for the standard XR6T engine.
The reality of intercooler performance equals:
- Largest intercooler surface area possible
- Optimal intercooler internal passage volume
- Lowest possible pressure drop ACROSS THE ENTIRE SYSTEM
- Greatest reduction of charge air temperature
- Highest possible intercooler core efficiency
- Matched to the turbocharger's air delivery in lb/min
The configuration of the front sheetmetal of the XR6T is a complicated affair when it comes to designing an intercooler to fit and perform. Particularly as the air flow through the front is partially obscured by a large bumper and impact beam assembly. Never the less, this demands that every available mm of width, height and depth is filled with a highly efficient intercooler core one that flows feely for the turbocharger’s maximum 65 lb/min mass flow rate and also removes the highest amount of temperature from the hot charge air. To achieve this, an exotic bar and plate intercooler core (rather than a radiator like tube and fin construction) with large internal passages and both internal and external fins must be utilized. In addition, the end tank design becomes critical to ensure that the charge air entering the intercooler is spread evenly through the intercooler core. This ensures that every mm of intercooler core is used and avoids any hot-spots from occurring in any particular part of the intercooler assembly.
The APS intercooler is unique in this regard. It is by far the highest performing intercooler core available for the XR6T and addresses all of the issues above.
However, whilst the core is the heart of an intercooler system, the ducting, getting air to the core and from there to the inlet manifold, are the veins and arteries. The biggest impact ducting has is upon the pressure drop across the entire intercooler system. As we have seen previously, ducting length is irrelevant in terms of response on the XR6T.
Since the role of ducting is to simply transport charge air, the actual route it takes is of little concern, other than designing it primarily for the lowest possible pressure drop and matching the air flow stream into the inlet manifold. A centrally located inlet/throttle body to the inlet manifold is considered mandatory to achieve an even spread of air to each cylinder. Otherwise, if there is any bias to flow in any particular direction from one side, the momentum of air entering the inlet manifold will result in one or more cylinders running lean or rich at different air mass flow rates (different power levels). Of course, the overriding factor is physical under bonnet space available for ducting whilst still maintaining practical sensible access to service items such as the battery etc.
Given the above requirements, APS designed the ducting system to complement the massive APS bar and plate intercooler. Ducting is sized to ensure the lowest pressure drop is achieved for engine power outputs in excess of 600hp. The standard air entry location into the inlet manifold is retained so that cylinder filling is as balanced as possible across the entire RPM range.
The point made earlier regarding the intercooler system forming part of the boost control strategy was an interesting situation. Ford had specified a very large turbocharger for the XR6T in order to move a great deal of air at low boost pressures. In order to keep the turbocharger boost pressure under control, a good deal of restriction was built into the intercooler system - along with a small turbocharger bypass. Once the restriction of say the intercooler was removed, the turbocharger boost pressure becomes uncontrolled and builds to alarming levels. The reason for this is that the turbocharger bypass orifice is too small to detour sufficient air from the turbine.
Ideally, the intercooler system should be removed from the boost control equation as it inhibits efficient engine operation at power levels above 350 kW. To do this, the turbocharger bypass issue must first be addressed. APS has engineered and offers as an option, the components required to vastly improve the bypass performance so that turbocharger boost control issues are resolved even at turbocharger flow levels beyond the capacity of the standard turbocharger.
The entire intercooler system is designed as a complete system for the XR6T and it addresses the XR6T specifically instead of carrying over technology used for small capacity Japanese turbocharged engines. Whether considering individual components or the entire APS intercooler system, a great deal of test, R&D and engineering has gone into each and every aspect specifically on the XR6T. This clean slate approach has resulted in engineering and product design effort being expended in the areas that truly matter in creating a high performance XR6T intercooler system.