Diesel Tuning

An introduction to turbodiesel special tuning.


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KitALLARDS have been associated with superchargers and turbocharging for more than 25 years and in that time have developed and fitted an extensive range of special tuning conversions and built up a considerable amount of technical expertise in this field. More recently we have turned our attention to turbo diesels, with the emphasis on the improvement of performance with optimum economy.

Typical Power Gains Fig 1Because of the way turbo diesels are set up at the factory to suit the average driver and urban driving conditions, many vehicles can have their performance improved by up to 25% with only a small increase in fuel consumption and a mild increase in maximum boost pressure. Our PHASE 1 tuning system can normally produce the unique combination of up to 10-15% increase in power and torque and in economy mode, up to 15% improvement in fuel consumption.

 An increasing number of turbo diesels are now equipped with an electronically controlled fuel pump. On these vehicles up to 25% improvement is possible when an uprated ECU is used in conjunction with one of our uprated intercoolers.

On a turbo diesel engine the fuelling curve relative to airflow into the cylinders is the critical factor. Too much fuel without sufficient airflow will produce an over rich fuel air ratio leading to smoke. It is important to have good boost available at low rpm to create sufficient airflow, but actually, boost pressure and the maximum boost are very much less important, provided sufficient cooled airflow is achieved.

 Increasing boost at lower rpm can be very beneficial, but in many cases just increasing maximum boost even if fuelling can be matched to it, will not necessarily increase power very much. There can be many reasons for this. One of the most significant is that modern turbochargers are of the low match type with relatively small compressor wheels working at very high speed. An increase in boost will increase the speed of the turbocharger, which can increase the air delivery, but air temperature rises more rapidly and the compressor runs out of its speed vs boost efficiency envelope. The rise in air temperature quickly offsets most of the increase in mass airflow, resulting in minimal increase in power and increased thermal and mechanical loads on the engine. The introduction of (VGT) Variable Geometry Turbochargers will improve volumetric efficiency over a wide rpm range, but the importance of an effective intercooling system will still be essential to increase flow, reduce thermal loads on the engine to minimise exhaust smoke, and to improve specific fuel consumption.

 Diesel engines will always be limited in their rev range as compared to a petrol engine and although they can be tuned in a similar way, e.g. with cylinder head modifications, change of camshaft etc., these methods are not particularly cost effective due to the amount of labour entailed and the renowned longevity of the diesel engine can be considerably reduced by this type of modification. This is why we concentrate on intercooling (charge cooling) and optimisation of the air/fuel ratio. Intercooling provides the most cost effective way of substantially increasing performance from tickover to maximum rpm, at the same time as having the potential to improve fuel consumption, reduce the thermal load on the engine and reduce smoke emissions. We have developed a range of complete intercooler conversions or an uprated intercooler, when one is already fitted as standard for many turbo diesels. Further installations are continually being added and we are pleased to quote for the manufacture for any vehicle which we do not already have an intercooler.

Typical Power Gains Fig 1

 ___Typical power gain
when fitting an Air to Air Intercooler with no boost pressure increase

- - - Further substantial increase possible with refuelling boost pressure and air flow


Allard air to air intercoolers come in many shapes and sizes to suit most requirements. An intercooler (heat exchanger) can provide uprated performance at the same time as reducing fuel consumption, exhaust emissions and thermal load on an engine.

Air to air IntercoolersIf your turbocharged or supercharged engine is already fitted with an intercooler, further improvements in engine power and torque are possible, often with no loss of economy, by fitting a larger capacity intercooler, which will improve air flow rates and heat dissipation.The incorporation of an intercooler in a turbocharged system is beneficial for two main reasons.  Firstly by cooling the compressed air being delivered to the engine, the air density is increased and thereby a greater mass flow is delivered to the engine. This in turn produces an increase in power output by allowing a larger quantity of fuel/air mixture to be converted to power. The second important benefit of intercooling is that by reducing the temperature of the ingoing charge the maximum cylinder temperatures are lower for a given boost, leading to a general reduction in thermal loading on an engine. In addition to these benefits, the reduced charge and internal temperatures permit the use of an increased boost pressure or compression ratio, which in turn produces more power and torque with a consequent improvement in performance. Because the increased boost pressure and lower charge temperatures are achieved from low rpm, the power and torque gains are spread over the whole of the engines  normal working range. Consequently with a substantial reduction in air temperature, negligible addition mechanical or thermal loads are imposed on the engine. Intercoolers are beneficial to all turbocharged or supercharged engines and where an intercooler is fitted as standard, further improvements can usually be gained by fitting an ALLARD intercooler with either a higher thermal efficiency and increased charge temperature reduction or higher air flow rating. This is particularly so if a higher than standard boost pressure is employed, when an efficient intercooler becomes even more essential.

Water to air intercooler systemsALLARD have many years experience of turbocharging and supercharging, and have designed and developed a range of air to air intercoolers (heat exchangers) together with installation kits, and related components for a wide range of vehicles and other specialist applications. Suitable for most turbocharged or supercharged engines (both petrol and diesel) including cars, vans, motorhomes, trucks, coaches, special purpose vehicles, tractors, and industrial equipment. The intercoolers are manufactured in aluminium to high quality, yet robust design. The tubes in the core are spaced and shaped to provide minimum flow resistance at high air flow rates, yet at the same time achieve optimum cooling of the turbo compressed air.  The finning both between and inside the core tubes presents a very large cooling surface to the compressed air, resulting in a substantial temperature drop across the core.

ToyotaHILUXWe can supply air to air intercoolers to suit most turbocharged vehicles. We have a range of kits and these can be fitted in our workshop or by one of our agents, or we can supply DIY kits with detailed fitting instructions.  We have facilities for the design, manufacture, fitting, and testing of intercoolers and intercooler installations to suit most applications. For instance, heat exchangers can be provided with built-in electric fan assemblies to assist cooling in conditions where the ambient air flow is limited under full load conditions, by the low speed of the vehicle or position of the intercooler assembly.