4.6 petrol engine in the P38 and as an upgrade for Discovery & Classic Range RoverThe 4.4 litre Jaguar/Ford engine from the Range Rover Sport

Petrol engine performance & tuning


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Start with the Buick 215 engine

From around 1965 as fitted to Rover sedans, the petrol engines were developments of the Buick 215 aluminium engine. Despite the high power and light weight of that engine, Buick ceased production in 1963 mainly due to oil and coolant seal problems. Land Rover purchased the tooling in 1965.

All are 90 degree V8 pushrod designs consisting of alloy blocks with iron cylinder liners. Over the years, they have been factory-fitted with various enhancements to improve performance. Early models with 3.5 litre engines had twin Stomberg carburettors and manual chokes that remain the choice for many off-road applications where electronic tuning facilities are not readily available. Graeme Cooper Automotive is one of the few remaining service providers able to tune these early engines to perfection

Electronic fuel injection

In 1986, the first electronic fuel injection appeared on Range Rover - a requirement for unleaded fuel use. It provided more power, better economy and easier starting, also relatively easier electronic tuning. In 1989, the original 3.5 litre version was replaced with a 3.9 litre GEMS version providing better torque and greater power output.

There are several variations of the 3.9 engine, including replacement of the multiple-belt system with a serpentine belt that is far easier to re-tension. However, this also meant that the (virtually unbreakable) oil pump was changed from its external location just above the oil filter to a different type inside the from engine cover.

Other changes occurred to the 3.9 setup over its 6 years, mainly with the fuel-delivery/monitoring system. The  Bosch  L-Jetronic ( the  Lucas 4CU Flapper), Hitachi Hotwire ( Lucas 14CUX) the GEMS systems and finally Bosch  Motronics were introduced progressively For some LSE models. Land Rover extended 3.9  to an engine a displacement of 4.3 L, with a crankshaft castings from the failed " Iceberg" diesel engine project increasing the stroke to 77 mm.

The 4 and 4.6 litre engines

In 1995, the "new" Range Rover SE and HSE P38 models had 4.0 and 4.6 litre engines respectively. While based on the same Buick block, the 4.6 version that was used until 2004 was considerably more powerful, smoother and with greater torque than any previous Rover engine. The revisions consisted of a new intake and exhaust system, extra block ribbing, revised pistons, and larger cross-bolted main bearings. 

The bad news is that the tooling for engine production had been used for over 25 years so tolerances were not what they used to be, also the distance between cylinders in the block arguably contributed to overheating, in many cases causing slippage of the steel cylinder liners inside the alloy block. This is fixable by replacing the original liners with top-hat liners. When the work is done by real experts (not all will qualify) and various enhancements are made during reassembly, tuning, these modified engines will transform a perfectly respectable engine into a beast of real power as has been demonstrated by several such conversions done by Graeme Cooper Automotive.

The BMW and Ford Years

Around 2000, BMW acquired the brand and progressively replaced Lucas with Bosch electronics, contributing considerably to the reliability of the vehicles. The 2002 introduction of the 3rd generation Range Rover occurred largely on the influence of BMW. The last THOR engines were made in May 2004, for the 2004  Land Rover Discovery.

Graeme Cooper Automotive has decades of experience maintaining, tuning and rebuilding the 3.5/3.9/ 4.0 and 4.6 engines, many of which remain in use today.

BMW sold the brand to Ford and the change to Jaguar engines occurred in 2005, introduced into the Land Rover Discovery. The Range Rover Sport was powered by a  supercharged 4.2-litre aluminium Jaguar 390 hp (290 kW) engine). A  naturally aspirated 4.4-litre 300 hp (220 kW version was also. Both petrol engines have sump and oil pick-up systems that permit operation at extreme angles. Due to lack of popularity, the naturally aspirated power plant was omitted from the UK market in 2007. 

The latest Land Rover engine developments

When Ford sold Land Rover and Jaguar to Tata Motors in 2008, the new company, Jaguar Land Rover, relied on Ford for all its engines. However, JLR opened a new engine plant in late 2015 and began producing its own Ingenium inline four-cylinder diesel and gasoline engines.

Tuning – what is does and does not do

There is much misunderstanding about “tuning.” Essentially, this means making whatever adjustments / enhancements that may be needed to maximise the power output. The fundamental rule is that no amount of tuning will improve an engine that is not running correctly in the first place, so basic maintenance is an essential prerequisite. Additionally, delivering additional power means putting more strain on other vehicle systems, especially the drive train, steering and brakes so these MUST be up to acceptable standards before attempting to gain power. Also, power and torque are two different things and the objectives must be made clear before commencing.

Remember too that the engine typically delivers less than half of its power to the wheels. Every related system robs power so the more gadgets are running (like air-conditioning) the less power there is getting to the wheels.

There are, of course, many different stages of “tune” from relatively simple improvements to power and/or economy, through to tyre-shredding increases to power at the wheels. Money is the essential ingredient. However, several things apply, namely:

Air intake is in many respects more critical than fuel to overall engine performance. What you have is mainly a function of the engine design but serious tuning may require anything from changing the air filter system to machining the inlets ports and/or changing the design of the inlet manifold.

Fuel flow & mixture – achieved through a combination of fuel rating (RON), pump pressure, size and cleanliness of fuel filters, the type and design of either carburettors or injection system, how the fuel/air mix is monitored and adjusted, usually by a computer-controlled engine-management system.”Mapping” the latter is serious science combined with extensive knowledge and experience. Changing the mapping of the ECU and/or using an after-market chip can increase engine output by 8% or more, but there may be negative offsets like engine longevity.

Ignition is a science all in itself. Depending on the model of the vehicle, it may have anything from a simple mechanical distributor and coil, through to a fully computerised system. The spark plugs themselves, any ignition modules and leads must be matched for optimum results. There is little point in fitting expensive plugs if the leads cannot carry the current and vice versa

Factory exhausts, like most other components are invariably designed and made to a price that involves many compromises. The aim is to get the optimum flow of gases away from the engine. Often, changing the muffler is a good improvement but replacing a standard exhaust system with custom headers (multiple pipes tuned to scavenge the gases) and larger bore pipe(s) can provide significant gains in power output, potentially up to a 10% improvement.

In conclusion, engine tuning is a combination of science and experience. It is most dangerous to accept advice and/or utilise the services of anyone other than a proven specialist.

The performance data graphed by our dynamometer for all of the various petrol engines may be selected from the following table

Data coming
3.9 Land Rover
4.0 Bosch
Data coming
4.4 BMW
4.4 Ford
4.2 Super Charged
Data coming

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