Understanding Engine Conversions

Having a vehicle that is performing well is important for reasons other than just speed and power. Improving reliability and efficiency will also result in better fuel consumption, hence reducing operating costs. In this article, we briefly look at common engine conversions for popular makes of 4WDs and we discuss the options for improving engine performance in regards to turbos, superchargers, extractors, exhaust systems and engine management chips.

What is Performance?

When purchasing a 4WD vehicle, performance is a key factor in the decision making process, however it can become a matter of ongoing importance when asking your vehicle to perform in off road conditions or when used for towing. These circumstances probably affect the majority of ExplorOz readers and hence form the subject of this article.

Manufacturers go to a great deal of trouble to find the best compromise in terms of performance, tractability and reliability for their vehicles. Most of us purchase a 4WD for the first time believing that the manufacturer has made the vehicle capable for the offroad conditions in which we intend to use it. However this is not always the case, and we find ourselves expecting more from our vehicles. There is a fair bit of truth to the adage that 4WD owners are tinkerers and always ready to try to do better than the manufacturer.

So let's assume that you've now decided that you need to improve the performance of your vehicle. What are your options?

Custom Conversions

There is a whole industry, and hobby, in converting four-wheel drives - installing different engines and transmissions in particular. For example, Chevy V8s and Holden V8s (4.2L or 5.0L) are the most popular transplants into Toyota Land-Cruisers and Nissan Patrols. Other conversions include Chevy V6s and Holden 3.8L V6s going into Nissan Navaras and Pathfinders. The Holden V6 is a neat fit in a Toyota Hilux. Corolla engines are popular replacements in older Suzuki 4WDs.

However we can't all go out and source an engine and shoehorn it into our new pride and joy. In fact, in so doing we introduce a whole range of possible reliability issues right across the drive-train of our vehicle, and with all tweaks and changes we make, reliability has to be one of the highest things on our shopping list along with safety.

So, for most of us, we're left with looking at how to improve the existing engine.

Petrol vs Diesel

It is true that in some applications, your choice of motor (petrol or diesel) may provide distinct advantages, however there are benefits for both in 4WD vehicles.

Reliability, simplicity, low down torque and better fuel consumption of the diesel engine in long haul outback driving is unquestionable. Coupled with the fact that diesel fuels are readily accessible in remote areas, a diesel engine is the logical choice.

However the flexibility, smoothness, instant power and broader rev range make the petrol engine better for general driving and especially good for escaping mud and sand traps as well as lunging up steep irregular hill climbs, where opportunities for traction may be limited, but the instant power of the petrol engine allows maximum momentum to be gained in a very short distance. Factors such as lower initial cost and faster warm up times, coupled with a higher power-to-weight ratio also means that petrol engines are better suited to shorter stop-start driving conditions.

With newer and more reliable technology giving both types of engine more power, economy and better overall flexibility, you will be able to make any engine more versatile and able to perform better under extreme circumstances. These factors somewhat reduce the arguable difference between the petrol and diesel engines used in 4WD vehicles.

For a more detailed discussion on this topic see our article Why Diesels are Different.

Increasing Engine's Output

Maximizing the power output of any engine is fairly basic in theory. Any engine modification that increases the amount of air and fuel flowing through an engine will increase power.

This means that when you're looking to upgrade engine performance, induction mods should be at the top of your list. Intake manifolds that flow a large volume of well-managed air, carbs, and EFI systems are designed to not only precisely meter fuel, but also provide the least possible restriction to airflow. Superchargers that force-feed an engine all the air it can use are components with a proven, and well-deserved, reputation for performance.

Turbos and Superchargers

A turbocharger will transform any vehicle, in extreme cases they can double the output of your engine however they generally are tuned for a 30-40% power and torque increase. In doing this they place much greater strain on all components of your engine. The trick is to gain the advantage of increased performance without unduly decreasing the life of your engine.

A turbo diesel can in fact have the equivalent top end power of a petrol engine while still benefiting from low down torque and better fuel economy.

Diesel engines by virtue of their increased structural integrity stand up particularly well to being turbo-charged. Many diesel engines these days come factory turbocharged, however there are a large number of after-market companies who provide excellent and reliable turbo units. While this may sound like the perfect solution, the problem is the extra cost. One of the advantages of the diesel is it's good fuel economy but you may decide that the extra cost of the turbo would more than pay for the increased fuel cost.

However, before considering adding a turbo to your engine you need to ensure that your engine is in generally good order. A tired engine and a new turbo is a recipe for trouble. Reputable companies will check the condition of your engine prior to fitting, and often provide engine reconditioning services also if required as part of the fitting service.

Superchargers open an entirely new concept in performance since a blower stuffs the intake manifold and the combustion chambers full of a larger volume of air than is possible in a normally aspirated intake tract. With the increased amount of air, more fuel gets in the combustion chambers and more power is produced.

A turbocharger works on the principle of utilising exhaust gases which are channelled to drive a turbine wheel in an exhaust turbine housing. Connected to the turbine on a common shaft but in a separate chamber is a compressor wheel. As this compressor wheel spins it supplies clean compressed air to the engine. A turbocharger literally turns waste into work. While doing so it increases fuel efficiency and reduces exhaust emissions. Some people complain of turbo lag where there is a slight delay in power response when you put your foot down. When a turbo is matched correctly to an engine, turbo lag is minimised.

Because superchargers are driven from the engine itself via a drive belt, the "lag" is greatly reduced however it uses some of the engine power (up to %) itself to run, albeit a negligible amount.

For a more detailed discussion on this topic see our articles Turbos and Super Chargers and Intercoolers.

Exhaust Systems

The role of the exhaust system is to take the spent gases away from the engine and allow for the next amount of the fuel air mixture to be drawn into the cylinders and go thru the ignition, burn, power and exhaust cycle. If the exhaust system is constricted then the burnt mixture is not all exhausted from the cylinders and hence there is less room to "get more in". Less in, equals less power and huge inefficiencies in the operation of the engine. Also see a more detailed discussion on the related issue of over fuelling in our article Why Diesels are Different.

To remedy this issue and provide easier breathing for the engine, a larger exhaust can be fitted. Exhaust sizes up to 2.5 or 3 inches (67mm to 75 mm) will improve the flow of exhaust gases from your engine however a common mistake is to retain the existing muffler. Exhaust size increase only, will give a small increase in engine power however, combined with a free flowing muffler will deliver considerably more increase in power.

It is also better to opt for a "mandrel" bent exhaust. This means that all of the bends in the exhaust are of the same diameter as the pipe itself. Under normal circumstances exhaust pipes are bent and the pipe deforms slightly in the area of the bend, the tighter the bends the more the pipe deforms and the smaller the diameter of the pipe at the bend. This means your huge 3" exhaust is maybe 2.75" on some bends introducing restrictions to the exhaust gases, eddy currents in the gas and overall reducing the effectiveness of the exhaust system. Mandrel bent exhausts avoid this and maintain the diameter of the exhaust for the entire length of the system.


Non turbocharged vehicles can benefit greatly from fitment of extractors. Extractors replace the exhaust manifold on the engine, which is like a common "rail" which direct exhaust gases from each cylinder out a single exhaust pipe connected to the manifold. Extractors have separate pipes for each cylinder, which are often tuned to ensure that there is maximum efficiency in eliminating exhaust gasses from the cylinder head. Some extractor systems are designed in such a way as to create lower pressure near the cylinder head with a venturi effect to actually help draw spent gasses from the cylinder. The effectiveness of extractors can be dependent on their "tuning" with some extractors more effective at relatively lower rev ranges - whilst others are tuned for higher performance and higher revs. Generally however, extractors are most effective in the upper rev ranges.

Extractors are traditionally used on petrol motors however they are also applicable to non-turbocharged vehicles however for my money, the fitment of a turbo to a diesel vehicle would be a more effective performance solution. Due to the higher compression ratio of diesel motors, performance is generally less affected by back pressure in the exhaust manifold, therefore diesels show less of a performance improvement than petrol engines from extractors. A petrol motor with its lower compression ratio is more affected by backpressure in the exhaust manifold.

Larger exhaust, extractors and free flow mufflers also have the added advantage of lowering running temperatures of vehicles due to getting rid of the hot gases faster.

Engine Management Chips

Sometimes called "piggy-back" chips, there are several manufacturers of these chips on the market. They are generally suitable for the range of modern injected diesel and petrol vehicles, although in a 4WD sense these are mainly applicable to diesel engines.

Manufacturers by nature set their vehicles up for a "standard" set of operating conditions. For example, all settings are optimised for a throttle opening of say 2100 RPM. The ECU (Electronic Control Unit) is programmed with those settings to cover the fuel air mixture, timing and other characteristics. Chip manufacturers claim that they calibrate their chips right throughout the rev range ensuring optimum performance across the entire operating range of the engine. They are also able to enhance the settings allowing higher fuel/air flow to produce a higher power output from the engine. The chip works "in line" with the engine to ECU communications and re-maps the instructions the ECU sends to the engine as it operates.

Chip manufacturers typically claim a 15 to 30% increase in power and torque. The units are supplied with appropriate connectors to plug the unit into the ECU and also to connect the engine to ECU cable to the chip. Fitting is simple. In use the chip is very impressive. There is a much better engine response, both off boost and on boost and the engine is far more supple and flexible, pulling strongly right throughout the rev range, due to the additional torque. Fuel economy is equal or better than without the chip, depending on how you drive and use all the additional power. Overall, a very good result for an outlay of around $1500. One benefit is the easy removal, if the unit fails or if you sell the vehicle, you can return it to the original specifications quickly and easily.

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Created: June 2008
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