Standard cylinder heads (shown above) contain a number of 'casting marks', left by the production process, that are very restrictive to air flow and speed.

The first stage in the porting process is the removal of these 'casting marks' and the smoothing of the surfaces over which air will flow. Although this does not greatly increase the volume of air that can be delivered by the ports on the head it does promote better air speed and less turbulence in the induction tract and therefore is a worthwhile process on mildly tuned or forced induction applications.

The picture below shows the inlet ports in the initial stage of "porting". The ports are very slightly larger than standard but essentially they are just smoothed and polished. (note that the guides have been removed at this stage)

"Stage II" Cylinder Heads

The next step in the modification process is to remove a considerable amount of material from the exhaust port castings to increase the volume of the ports and allow for greater volumes of air to be scavenged from to the cylinder.

This in turn requires that we shape the ports correctly to prevent turbulence and 'stalling' of the air in the induction tract.

"Stage II" heads will function well in most engines where the capacity does not exceed 3.9 litres, or where forced induction is being used to push the gas mixture into the cylinder. The Stage II exhaust ports allow for greater horsepower to be produced without reducing the speed of the air in the induction tract, essential for the production of mid range and higher output.

There are options available for the mixed sizing of the ports to accommodate supercharged engines and if Stage II- heads are to be properly designed a good understanding of the proposed usage is normally required; consultation with the customer is essential.

"Stage II" Cylinder Heads

Things are getting more 'serious' now! At this stage of development the cylinder heads are ported and polished to achieve full air flow on anything up to a mildly tuned 5.2 litre engine. The valves are now bigger and allow a greater charge of gas to be drawn into the chamber. Guides are shortened and 'bulleted' (basically this 'bulleting' reduces the port restriction caused by the guide in the port). Combustion chambers are very precisely matched to give equal volumes of gas for each firing.

Valve springs are changed for much stronger double springs with a progressive pressure to suit the proposed camshaft.

The exhaust ports are opened to match the largest of exhaust gaskets.

The inlet ports are opened to match a 45mm ported inlet manifold.

At this stage the heads are good enough to flow the air and fuel needed for a 4.6 litre engine to produce over 320 BHP as opposed to the standard heads which are capable of little more than 220 BHP.

The head chamber are also ported and polished and will match to the other chambers on the head prior to completion.

"Stage IV" Cylindert Heads

At this stage of development there is no material left to remove! We port the heads to the greatest possible volume through from inlet port to exhaust without losing the mixing and speed aspects of the induction tract.

The valve seats are removed and replaced with larger versions to accommodate even larger valves than the Warrior head.

These heads have been used on engines producing in excess of 360BHP and will probably deliver even greater power if combined with an ideal injection system. In terms of a standard Rover casting, they don't get better than this!

The heads have a 'skimmed' cylinder face to ensure correct gasket sealing and optimise compression ratio.

Notice the shortened, bulleted guides and the chamber shaping. The combustion chambers have been ported, polished and precisely matched for size (capacity) and shape.

Lucas 4CU:

This system is often referred to as 'Flapper'. This nickname is derived from the air flow sensor that is used to manage the fuelling system. The 'air flow meter' resides in the inlet tract, usually just behind the filter, and by the use of a spring loaded 'flap', tells the management system how hard the engine is 'sucking' in the air. This then allows the engine to adjust the time that the injectors open per pulse and therefore controls the amount of fuel being delivered. In conjunction with the airflow meter a 'Throttle Potentiometer' is used to determine the amount of throttle being applied. There are a two other sensors that have a bearing on the fuel delivery, firstly the engine temperature is measured by a sensor on the inlet manifold and secondly the rpm of the engine is picked up from the negative side of the coil. All of this information is fed back to the Electronic Control Unit (ECU) which then adjusts the injectors 'pulse width'.

Although this is a fairly basic system with an almost 'linear' approach to the mapping of the fuel delivery, it can be effective in high performance applications where the engine is almost entirely run at very high throttle positions and idle / fuel economy are of less interest. The system is very old now and some parts have become completely obsolete, the throttle potentiometers are almost impossible to find although modifications can be made to run a newer version.

Flapper systems are found, in the main, on early SD1 cars (both single and Twin Plenum), early fuel injected Range Rover Classic, TVR 350i, early TVR 390i and some Morgan V8's. There were also a number of modified versions with adjustable ECU's made by Mark Adams (Tornado). As mentioned earlier this is a fairly basic system with a number of inherent drawbacks but is still functional and can be modified and tuned for greater performance if wished.

Lucas 14CUX:

Often referred to as 'Hotwire', this younger version of the Lucas system utilises an 'Air Mass Meter' which reads air mass by means of a heated wire inside the airflow meter. The system itself is very similar to the Flapper version but with a few 'upgrades'. The injectors are slightly better and the measurement of air mass rather than air flow means that the system works better over a range of atmospheric conditions. Basically speaking the air intake 'mass' is more accurate because it changes as air density, temperature and humidity change. This means that the Hotwire system can cope better with changes in atmospheric pressure and temperature and therefore the engine tends to run equally in all conditions. Unfortunately the fuel mapping system is not greatly enhanced and is still a little two dimensional for high performance use but the system is definitely an improvement over the Flapper.

Hotwire systems are very widely used and can be found in TVR Griffith & Chimaera, TVR SEAC, TVR 390i, Westfield, Range Rover Classic and many other uses of the Rover V8 engine. For the most part it is well supported and spares can be found quite easily for most of the components used. The system is quite sensitive to adjustment and it does pay to have someone who knows the system well to set it up, even small adjustments can make a substantial difference to the way it runs.

There are a wide range of enhancements available for the Hotwire system. Mark Adams produces the 'Tornado' chips which do a far better job of controlling the fuelling than the standard versions. Fitting larger plenums, inlet manifold and trumpet bases can enhance power output enormously. The system can also be modified to use a larger air flow meter and even higher flow injectors should they be necessary. The Hotwire system can be set to use narrow band Lambda sensors for fuel adjustment below 3000 rpm which can help with fuel economy and idle control, this can equally be disabled with a simple resistor change.

There are of course also a number of concerns! The Hotwire system is renowned for losing idle control... this is usually caused by a failure in the 'stepper motor' that controls an air bypass to the plenum but is also somewhat attributed to ECU faults and sensor faults elsewhere in the system. Whilst this is not usually damaging to the engine it can be very frustrating and difficult to cure. We would strongly recommend that a only seasoned professional attempts the set up of the system! Trying to make adjustments with little knowledge of the system can result in engine damage and large bills!

GEMS:

This system is found in the main on Range Rover P38 vehicles, either 4.0 or 4.6. The GEMS system is not dissimilar to the Hotwire system in many respects but does have some notable differences. Firstly GEMS systems use Distributor-less Ignition (DIS or Coil Pack) rather than a standard distributor. This is a far better system for the delivery of a spark to the plugs and limits failure points by the removal of a distributor, rotor arm and spark delivery cap. Secondly this system is under constant Lambda sensor control. Twin Lambda sensors in the exhaust manifolds control the fuelling across the rev range by reading the air / fuel mixture in the exhaust gasses and adjusting the input fuelling to achieve an ideal burnt emission. This is excellent for maintaining emission control and means that very little adjustment is required in the system when setting up. Unfortunately this does not enhance power output. Generally speaking, a performance engine will run slightly 'richer' than normal at high load and high rpm and GEMS does not allow for this. The result is, when everything is working correctly, a very smooth engine and smooth power delivery but not much 'go' above 3000 rpm, not ideal for a sports car or race vehicle but better for a road going car where performance is not a big issue.

There are some enhancements to be made. There are chips available which alter the target fuelling and therefore performance but they are never going to be capable of turning a stock road engine into a high performance, fast road car whilst being controlled by their emissions. All in all the GEMS system is very good but does have it's limitations.

THOR:

I really have no idea why this system has been given the name 'Thor'!! This is the BMW-inspired injection system fitted to very late Range Rovers. It is identifiable by the inlet manifold which replaces the Plenum chamber found on earlier versions and resembles a bunch of bananas! Although the engine management system bears the efficiency and accuracy of the BMW lineage, power output above 3000 rpm is seriously hampered by the inlet manifold arrangement. The engines produce good torque figures and do run well, but power is definitely sacrificed.

The Rover V8 standard valve train consists of Steel Rocker shafts held in place by four pedestals and holding 8 rocker arms per head. The rocker arms are generally of aluminium construction although there are some steel versions on the market that look very similar to the standard items. The rocker arms themselves are fitted with a 'cup' at the pushrod end and a steel shim or pad at the valve end. These pads are slightly curved to allow the valve to 'slide' across the top of them. The standard construction is not the best of rocker assembly designs. The pads tend to wear a groove from the top of the valve and can often fracture or simply break away resulting in very noisy valve gear and subsequent follower and engine damage. There are aftermarket options available including the 'Yella Terra' roller rocker system and so called 'Group A' adjustable rockers but they are expensive and difficult to get hold of.

The standard engine is fitted with hydraulic camshaft followers (lifters or tappets) and these provide a degree of 'pre-load' within the valve train. Basically speaking the follower is oil filled and has a small spring at its centre. The centre of the follower is free to move within the outer shell and this is the part where the pushrod seats. The 'cushioning' effect of the oil filled follower means that the valve, follower , pushrod and rocker remain in contact at all times (effectively).

Pushrods are of solid construction with 'balls' on either end. As the cam rises and pushes the follower up the pushrod then transfers this movement to the rocker arm which in turn rotates and pushes the valve (with its spring) down into the chamber, opening the valve and allowing the air / fuel mixture to be drawn into the cylinder. 

in progress

1) The 'pre-load' measurement is taken at the top of the follower and is the distance that the inner plunger is depressed below its retaining circlip. This is really very difficult to measure and we therefore have a slightly re-worked method for making the measurement.

2) With camshaft and followers fitted and the pushrods located on the followers, start to fit the rocker assemblies but do not tighten them down. Check that the camshaft lobe for number 1 inlet is 180 degrees opposite the follower (the follower is at the lowest point of its travel). Slowly tighten the rocker assemblies by turning each of the four bolts in succession (half a turn at a time) until the gaps at the valve side and the pushrod side are closed. At this point you should have no depression on the inner plunger in the follower (it should be at the top against the retaining clip) and the pushrod should be easily spun between your fingers but not able to move vertically up or down easily. Then using either feeler gauges or an accurate vernier caliper, measure the gap between the rocker pedestal and the cylinder head. This measurement will tell you what the pre-load will be without the rocker ratio being taken into account, in order to get the accurate pre-load measurement then use the formula;

Pedestal gap measurement x 1.6 = Pre-load at follower

3) we are looking in most cases for a pre-load of between 0.040" (40 thou) and 0.100" (100 thou) although this is not always the case so please ask if your installation is unusual or non standard.

4) Let us assume that your measured pedestal gap is 0.100" (100 thou). This would mean a pre-load of 160 thou which is too much and therefore the pedestals need 'shimming' to reduce the pre-load. By using the same calculation in reverse it follows that a 0.050" (50 thou) shim will reduce the pedestal gap to 0.050" and give us a pre-load of 0.080" (80 thou) which is acceptable. The shims generally come in thickness's of 0.016", 0.032" and 0.050" so it does not take a genius to adjust the pre-load to within parameters for most instances.

5) What if the pre-load is too low? This is more of a problem! There are a couple of decent solutions; a) have the pedestals machined down by 0.030" to 0.050" and then repeat the pre-load checking procedure or b) use adjustable pushrods to alter the length of the pushrod and therefore the pre-load on the follower. Both of these options have drawbacks! The pedestal machining is expensive, difficult and not always very accurate. The use of adjustable pushrods is a much better solution but most adjustable pushrods are slightly thicker than standard Rover versions and may need the guide holes in the cylinder heads 'opening' slightly to allow for contact free movement (this is a simple drilling exercise!).

Leaking Liners?

Although there is little definitive information as to why the cylinder liners on some Rover V8 blocks appear to become 'porous' or start leaking, the most popular theory revolves around a flaw in the block casting.

It is thought that some blocks, particularly those used for the 4.0 litre and 4.6 litre engines, have a small casting defect behind the liners. This defect is between the water jacket in the cylinder block and the back of the liner. Over a period of time, water seems to cross the defect and end up on the back of the liner. This then works its way up the side of the liner and eventually causes a leak pathway all the way up to the block face.

This pathway allows the hot gasses from the cylinder to pass into the water jacket, pressurising the system and adding extra heat to the coolant.

Although at this point the problem is a minor one and may only appear from time to time, it does worsen over a period of time and eventually causes the engine to overheat and expel its coolant on a regular basis.

The worst case scenario is that the engine is stopped with substantial pressure in the water system and the water then is pushed back into the cylinder. If the water is still there when the engine is re-started it cannot be compressed and a 'hydraulic lock' occurs which tends to bend connecting rods, warp heads, lift head gaskets and is generally not very pleasant!

How do we check for leaking liners?

It's a good question! Unfortunately it is not the easiest of things to accurately diagnose 'in the car'.

The first problem is that the leak is often only noticeable when the engine is warm. We can check the water system for the presence of Hydrocarbons, which does identify a problem, but could equally be attributed to a blown head gasket which shows almost exactly the same symptoms as a leaking liner.

We can run a 'leak-down' test which is a little more definitive. Because the only connection point between the cylinders and water jacket is on the end cylinders (1, 2, 7 and 8) a leak-down test that shows leakage into the water system on a central cylinder (3,4,5 or 6) can only be a liner problem.

The leak-down test needs to be performed with the engine at normal running temperature and with the engine rotated to the correct position to have both valves closed during pressurisation.

The only absolutely definitive test is a pressure test of the block alone. This involves a completely removed and stripped engine, a number of blanking plates, an oven and 130 psi air pressure!

Obviously this testing requires time, effort and subsequently cost. The best advice we can give is that if the symptoms are there, run the first three checks and hope that something definitive is found, if it is not then I am afraid the bottom line is it is almost certainly a liner issue and you need to start making a decision as to which route to take next.

The Remedy