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Dermot's Lotus Esprit S4 Sport

Time:2017-09-28 00:23Turbochargers information Click:

Lotus Esprit Lotus Esprit Tur

1. Ignition System

Spark Plug

Iridium spark plugs. Iridium has a melting point of 2450°C, considerably higher than Platinum, and its strength - approximately 8 times that of platinum.  As a result the spark plugs centre electrode can be made with a much smaller diameter than with platinum types, Gold or gold palladium and copper/nickel types. This means that spark plugs potential difference is more concentrated and hence less 'spark jump' voltage is required - this can be as much as 5,000 volts less than with standard plug types. Ignition is improved and less strain is placed on the ignition system. Benefits of improved ignition/combustion include better fuel economy, increased power/acceleration and especially better throttle response.

Standard Lotus spark plug is a NGK EPR6EKN. The direct cross to the Denzo iridium plug is an (IW20). I have gone for a slightly cooler version the IW22.

2. Fuel System

Sytec fuel pump. The standard S4 fuel pump is a roller vane type, high pressure electric fuel pump mounted within the right hand fuel tank. The pump supplies fuel at 30.5-55psi to the fuel rail. On the Sport 300 the fuel pump was upgraded to a higher capacity pump as fuel starvation was experienced in testing. Unfortunately the Sport 300 pump is now obsolete and so an alternative up rated delivery compatible in-tank pump was sourced. The Sytec pump chosen is able to support motors with over 400 hp.

Fuel tank treatment. As a preventive measure when the engine and gearbox were out the fuel tanks were sent away for re-coating and rust proofing. The tanks were treated using the ReNu system by Arrow Radiators Ltd, in Melksham. Fuel Tank ReNu coats both the inside and outside of the tank, sealing it from rust and corrosion. Fuel Tank ReNU is completely compatible with petrol, high octane fuel or methanol.

 

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manifold

Fuel manifold. The aluminium fuel rail receives fuel at its forward end and

fuel rail

supplies all four primary injectors. The fuel pressure in the rail is controlled by a fuel pressure regulator fitted to the other end of the rail. The pressure regulator assembly is a diaphragm operated relief valve with fuel pump pressure operating on one side and regulator spring pressure and manifold pressure on the other. The function of the regulator is to maintain a constant pressure differential across the injectors at all times ie. a constant difference between fuel pressure supplied to the injector and inlet manifold pressure at the port injector nozzle. The Sport 300 was fitted with a slightly higher fuel pressure regulator. The Sport 300 regulator is now obsolete, for a number of reasons I have decided not to increase the fuel pressure in the rail but rather change the injector sizing's.

 

 

 

fuel rail

 

 

 

 

Fuel injectors _ Primary The stock primary injectors are low impedance (2 ohms) 370cc/min or 36lb/hr "peak and hold" injectors. The Lotus OEM ones have been frequently been deplored for their poor design and spray pattern. Blue-printed and matched primary fuel injectors were sourced from John Welch. They are 370 cc/mm RC Engineering injectors which are matched to a 1% tolerance flow rate. My advice is to upgrade the quality of the primary injectors but do not increase the flow rate. To increase the fuel delivery potential upgrade the secondary injectors

Fuel injectors _ Secondary Although the two plenum secondary injectors are similar in construction to the primary injectors they are actually high impedance (16 ohm) 190 cc/min or 18 lb/hr saturated type injectors. These injectors operate at a fixed frequency of 128 Hz, with the quantity of fuel delivered dependent only the pulse width sent by the ECU. The stock S4 ECU fuel mapping only triggers the secondary injectors over 4800 rpm and 0.7 bar boost. I have fitted 270 cc/min (25.7 lb/hr) RC Racing high impedance injectors. If you are undertaking major engine mods it is very important to think about the correct fuelling. The ECU goes into "open loop" mode above 94% throttle openings, in open loop mode there is no feedback to the ECU from the lambda sensor, under these conditions fuelling is based on pre-stored fuel maps in the ECU.

Picture on the right is an image of the 2 secondary RC injectors on the bottom compared to the standard Bosch injectors.

RC Racing have a nice tool to work out the amount of fuel you require for a specific hp figure. Go to their technical section.

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