GMR is a design & engineering company with a unique advantage: our background is in military aircraft engineering.

It leads us to err on the side of over-engineering.  Instinctively and deliberately.  It sets us apart from most automotive engineers, and we make no apology for it.

It means that every aspect of our automotive and mechanical work is exhaustively scrutinized and tested from design to function with tolerances to match.  The result is that our designs perform exactly as they should, have exemplary fit and finish, and last a very long time indeed.

We like to think that our design ethos resonates with that of another unique British automotive manufacturer whose state-of-the-art technology is applied by craftsmen: Aston Martin.

The team

We have a small and friendly team, ready to answer your questions… although the really technical ones we leave to Graham!

The man behind the design…

Graham Heane, managing director


 

Ali – supports Graham on technical & service

Paul – strategy, supplier liaison & finance

Jan – field team & logistics

Andrew – marketing & events

Unlocking the V8 Vantage’s potential whilst retaining its character.

It was clear to us from an early stage that forced-induction was the key to unlocking the V8 Vantage’s potential whilst retaining its character.  The question was: which means of supercharging?


Firstly, turbochargers and the centrifugal type supercharger:  these units provide most of their power and torque in the top one third of the RPM range. Whilst this is fine for small, high-revving engines requiring more power, it does not suit the characteristics of a V8 from Aston Martin.

That left us with Positive Displacement superchargers, of which there are two kinds: Twinscrew and Roots.


The Twinscrew, (of which, in turn, there are two sub-types: ‘Lysholm’ and ‘Kenne Bell’). The twinscrew has always been regarded as the most efficient of the Positive Displacement  designs thanks to its use of interlocking screws to generate compression.  It works in the following way:

 

The screws are mounted close together, side by side.  The blades of each screw fit between one another, like the teeth of interlocking cog wheels.  However, unlike cog teeth, as the screws turn, each pair of blades moves slightly further apart, generating a vacuum.  Air is sucked into the vacuum generated in the gap between the blades.  This makes for a very efficient air pump especially when pressures above 12psi are required.  However, it does have some disadvantages.  Principally the fact that it is constantly compressing the charge whenever the engine is running,  which consumes power and generates heat, even when off-boost.  Secondly, the vacuum effect generates a ‘popping’  sound  when the charge is expelled from the screws into the manifold, which manifests itself as a high-pitched whine as the boost rises beyond 10 psi.  For these reasons, twinscrew blowers are typically fitted to racing engines and other engines requiring substantial and constant boost.


The Eaton Roots: these have been the blower of choice for most road car manufacturers because they are able to generate prodigous levels of boost at low engine speeds, whilst at the same time being reliable and quiet in operation.  Most importantly, when off-boost they do not generate heat or significant drag on the engine.  Like the Twinscrew, they feature rotors, but the key feature is a bypass valve which directs the air away from the rotors when not needed.  When the accelerator pedal is depressed, a partial vacuum is generated in the manifold, causing the bypass valve to close and direct air through the rotors, which compresses the air to generate boost.  Unfortunately they are also the least efficient type of blower,  being only on average 55% thermally efficient, compared to the other types’ thermal efficiencies of 75% (centrifugal), and 70% (Twin Screw).  A typical turbo-charger is 75% thermally efficient.

 

Because of their relative efficiency ratings, the Roots design always had to give way to the Twinscrew when boost  beyond 10 psi was required.  Things have now changed with the introduction of the Twin Vortices Series (TVS) supercharger by Eaton.  Whilst still a ‘Roots’ this range of blowers features a pair of screws not dissimilar to those of the Twinscrew.  However, the design of the TVS screw is revolutionary:  it features four blades instead of three,  and each blade ‘twists’ 100 degrees further.  These two innovations have allowed Eaton to do the apparently impossible and create a supercharger that beats the Twin Screw on efficiency, noise and power consumption.  It has a thermal efficiency of no less than 76% over most of its operating range  and is far quieter in operation than the previous designs.  It also only uses 0.3 of a BHP to drive when off boost.  This is the one we use in GMR systems.


The V8 Vantage has a compression ratio of 11.3:1, which is high for a road car and so limits the amount of boost it can take before detonation occurs.  Even with the TVS unit we still need to cool the charge, and for this we use water.  See “The Geyser“ below.

Lowering the temperature of the charge (i.e. the fuel/air mixture)

Our Geyser System is a modern version of the water injection process developed for aircraft engines during the Second World War.   The process was developed in order to lower the temperature of the charge (i.e. the fuel/air mixture), whilst at the same time acting as an anti-detonant  (i.e. avoiding ‘pinking’ or ‘knock’).


It works in three ways:

1) Water is injected into the manifold as a very fine mist through nozzles at over 100 psi.

2) The water changes state by evaporation into vapour, absorbing heat as it does so.  This process instantly cools the air within the manifold (compression of air by a supercharger also, inevitably, heats it).  The system is so efficient that the compressed air can be introduced at almost normal atmospheric temperature.

3) In the combustion chamber the remaining vapour turns into steam. The effect on the engine is to reduce cylinder temperature. This improves the dynamics of the ‘flame front’ which means that the fuel/air mixture burns in a slower, more efficient manner, giving the piston a less violent ‘shove’.


In conventional engines, the only way to achieve this cooling effect is to add more fuel.  This is exactly what manufacturers of modern production cars do: more fuel is added to richen the air/fuel mixture under load, purely in order to reduce the in-cylinder charge temperature.

 

As well as being cheaper than fuel, water is far better at cooling air: it has six times the ‘latent heat capacity’ (i.e. ability to absorb heat) of fuel. It also has the side effect of steam-cleaning the inside of the combustion chamber, removing the carbon deposits that cause ‘hot spots’, which can cause knock.

 

So, by adding water to the charge instead of fuel, a leaner fuel/air mixture is usually possible. A substantially leaner mixture is possible under load, because fuel is not wasted by being used as a coolant.


The result is efficiency gains everywhere:  an improvement in fuel economy, at the same time as increasing output at all engine speeds, and cleaner exhaust emissions.

Our Geyser system is an advanced version of water injection, precisely calibrated by our own software for any given engine.  The water is pressure and temperature controlled by the system so that there is no danger of excess water entering the cylinders and thus risking corrosion.


Why not use an intercooler?

An intercooler is merely a heat exchanger.  It is only as effective as the ambient air temperature – some days hot, some days cold –  and it does not perform as consistently as water injection.  But the main reason is that a heat exchanger simply cannot cool the charge as efficiently as spraying water molecules directly into the air.  Our modelling of the system shows that there would be a boost loss through the intercooler of around 1-2 psi. This would be self-defeating in our low-pressure system, as the supercharger would have to spin 25% faster to achieve the same boost, adding to the generation of heat and adding stress to the engine.


Thanks to our Geyser system, the supercharger runs at an exceptionally low boost pressure of only 6.5 psi.

‘Any gear, any RPM, just add water’!

System Safety

SYSTEM SAFETY AND INTEGRITY

An unwritten law that sets a quality upgrade apart from a cobbled together set of aftermarket parts, includes that all vehicle management systems retain their integrity. By that we mean all the vehicle’s safety systems that were integrated ‘at birth’ (i.e. chassis, engine management and maintenance), must remain in place to look after the vehicle after the upgrade.


CHASSIS SYSTEMS

These must include ABS, any stability control programmes, anti-skid, traction/torque control, etc. Any changes to the operation of these systems would render the upgrade a ‘downgrade’, and have no place on the commercial market as a road car. This is not the case for track cars that operate under different rules and by different drivers.


ENGINE MANAGEMENT SYSTEMS (ECU/PCM)

This is also important as many aspects of the vehicle’s safety systems rely to a greater or lesser extent on the ECU/PCM for information and/or operation. Many, if not all cars built these days have an incorporated ‘drive by wire’ throttle system. This is regarded by some as an over-complication of a simple process. What is misunderstood is the part this system plays in the overall safety of the vehicle. For instance, traction/torque control/stability controls are all governed to a degree by the ‘drive by wire’ throttle. Just because the driver mashes the pedal to the floor does not necessarily mean that the throttle will open to the same degree. In a millisecond the ECU will calculate the most efficient throttle plate angle for engine speed, car attitude and grip available. Far from being a hindrance to the driver, it must be considered a friend as it’s taking into consideration far more aspects than an average driver is able to assimilate, especially on the way to work in the morning when he or she is thinking about the kids, the troubles at the office and the events of the previous evening, etc! Whilst we humans are thus otherwise occupied, the Engine Management System is keeping a constant watch over the safety of the vehicle.

There are many systems built into the ECU solely for engine protection and emissions. Again, these cannot be compromised. The ‘knock’ and ‘lambda’ sensors play a huge part in how the vehicle drives, the fuel economy and not least engine safety. Any omission or changes to these systems must spell danger to the purchaser and should be avoided.


Of special importance is the open/closed loop lambda system:

For all the extra air being ingested when under boost, it is vital that the Air/Fuel Ratio is maintained to levels that are vital for the safety of the engine. These are under low load ‘closed loop’ conditions (AFR 14.7:1), high load ‘open loop’  (13.2:1 max torque to 12.5:1 max power). Should any irregularity to these be seen by the lambda system, it will bring on an Onboard Diagnostics  (OBD) code showing either  ‘lean condition’ (can cause detonation). Alternatively ‘condition rich’, which can severely deteriorate the catalytic converter. Should either condition be present an immediate code is shown. It will also identify the offending bank and the associated condition.

 

The knock sensing capacity of the AMV8 engine is also key to its ability to make timing allowances for lower grade fuel (unlike it’s bigger 12 cylinder brother which cannot change its timing to accommodate such a change). Therefore, this system must also remain completely intact with no interference from an ‘outside party’, namely another ECU, etc.


Here at GMR we take special care to ensure that all of the above are retained. Our systems are integrated to run alongside your car’s existing system and in no way affect the complex monitoring systems in place as set out in the OBD2. Nothing is hidden and should any of the engine systems be outside these parameters then the PCM/ECU will bring up the associated warning, as it would prior to the upgrade.


MAINTENANCE

Normal maintenance procedures and service timings can be adhered to. The only additional requirement is to examine the supercharger belt at service: 24000 miles or 3 years whichever comes firstIn addition the supercharger gearbox oil will need changing after 250,000 miles!


YOUR CLUTCH:

Our development car has completed over 77,000 miles in supercharged form (@ early 2016). The clutch has covered 57,000 miles (including many test drives and track sessions) with no detectable deterioration in either feel or travel. This is indicative of the benefit of the conversion, as the car now only has to do half as many gear changes as it used to, due to the greatly increased torque available at low RPM’s in the higher gears. So much less use of high RPM gear changes means that the net result is substantially less shocks and stresses on the drive train as a whole. That said, we are not recommending supercharging your car simply to extend clutch life!

“All vehicle management systems retain their integrity. By that we mean all the vehicles safety systems that were integrated “at birth”, must remain in place to look after the vehicle after the upgrade”.