Sanningen om att trimma Esprit V8:an (typ 918).

[Lasse]

Nedan följer lite intressant "officiell" information från Lotus om vad man bör ta i beaktande om man vill trimma sin Esprit V8.

The V8 Engine.

More than pistons need to be considered when 'chipping'. The specification of the V8 Engine was generated to produce a production engine that met the requirements of Vehicle Performance and Type Approval regulations for the markets it was to be sold in.

To get the performance targets, economy, emissions requirements and of course build costs laid down at the project proposal time the engine specification was generated to meet that specific conditions. The Engine needed about 350 BHP to meet the 175 MPH top speed Economy was important as the model (4 Cylinder Turbo) it was replacing was considered economical for such a performance car.

The emissions level had to meet the latest USA requirements (as it would be a world spec. car) The component & build costs had to be carefully considered as the engine was changing from a 4 cylinder to an 8 cylinder unit. (more components) It must also be noted that the engine torque had to be limited to 400 Nm as this was the maximum that the driveline can handle without a new Gearbox, Driveshafts and Rear Hubs.

There was a company decision that the engine would be Turbocharged and have a Flat Plane Crankshaft. As the Engine Development progressed it was confirmed that the Engine Torque would have to be 'capped' in the mid range to comply with the 400Nm torque
limit. The end result was:

* An engine that produced 350 BHP at 6500 RPM.
* The 'Max. Torque' limit resulted in the engine having close to 400Nm for most of the Rev. Range.
* The component specifications were generated to produce an engine that met the above requirements and gave the required durability of over 100,000 miles.

This resulted in the engine having 'conventional' Cast Pistons and Iron Liners compared to the latest Lotus 4 cylinder (910) having Forged Pistons and Aluminium Liners. As the Turbo Pressure is relatively low it is easy to 'pump up the Boost' and increase the fuelling with a change in calibration (new chip) to produce more than 350 BHP and uncap the mid range torque to exceed 400 Nm. With the engine running in this condition it generates more loading on the pistons and bearings and produces more heat which has to be dissipated by the water and oil.

The pistons are not designed to cope with more than 350 BHP for any length of time and the big end bearings are not designed to work with the increased loading. The extra heat generated needs to be accommodated by the cooling system that is only designed for the original engine power output

The result of running a chipped engine is as follows:

* Overloading the Pistons. Melted pistons is a known problem
* Overloading the Bearings. 'Big End' bearing failure has been seen
* Turbo overload. Turbo will be operating outside the manufacturers designed envelope
* Overloading the Cooling System. This can result in the engine running hot and coolant being expelled from the cooling system which can lead to high oil temperature and engine damage
* Catalyst overheat. Cat can be destroyed by excessive exhaust temperature & overfuelling
* Overloading the Gearbox. Broken gearbox shafts
* Overloading the Clutch. Clutch failure
* Overloading the Driveshafts. Broken driveshafts

The above applies to both 4 cylinder & 8 cylinder Lotus Engines. Most of the mechanical failures due to increased power will be of the fatigue type - happening over a relatively long period so the initial performance improvement is appreciated for a limited period of time. This time depends on how much 'right foot' is applied by the driver. If restraint is used the engine can last a long time before any problems become evident.

All that can be guaranteed is that the 'Engine Life' will be reduced considerably and other components such as Gearbox & Driveshafts exposed to driving conditions they were not designed for. Such driving conditions may make the vehicle unsafe to drive on the Public Roads

All the vehicle specifications that are produced and built by Lotus are fully tested and approved. All the Engine specifications are developed on an Engine Dyno which includes complete Engine Mapping & Performance,

In Vehicle testing includes the following:
Vehicle Performance, Emissions, Cooling System, Heating System, Ride & Handling, Altitude, Hot & Cold Drivability, Brakes (ABS), Abuse, Road & Track Durability.

The above testing ensures the integrity of the specifications.

(Källa: www.lotusespritworld.co.uk)

Mvh /Lasse

[Mikael_W]

känns tryggt att man då kör en originalbil utan någon chippning