Lotus Esprit Silhouette Special
This is a totally unique Lotus Esprit race car that has been built specifically for motor racing. It is built to Special Saloon regulations which allow the car to be very different from the car on which it is based whilst maintaining the appearance of that base car, the main requirements are that the side silhouette, windscreen shape and wheelbase are to be maintained.
I was lucky to take some photos of my Esprit alongside a very nice Lotus Esprit Turbo S3 where the similarities between the cars can be seen.
To be competitive the car needs to have a high power to weight ratio, to achieve this the car needs to be as light and as powerful as possible. To achieve this the car is built around a tubular steel space frame which includes the roll cage structure, engine & suspension attachments points and other structural attachments for things like the seat / pedals / battery, fuel tanks etc.
To keep the weight to a minimum a range of structurally efficient materials are used;
Aluminium – Engine & intake manifold, floor panels, bulkheads, radiators, oil tanks. Magnesium – Wheels, suspension uprights, gearbox and bellhousing. Carbon Fibre – Roof, rear bodywork, rear diffuser and bonnet. Fibreglass – Front bodywork and doors. Other materials include titanium for bolts and heat shields and Plywood for the front splitter and side panels.
The engine fitted to the car is a very special 5.5 litre Chevrolet LS6 race engine as used in a Daytona Sports Prototype race car in the USA. The engine parts were sourced from the USA and then I rebuilt the engine myself with advice from a few engine builders in the States.
The engine produces good power, on the hub dyno at RDT it put out 509 bhp at the wheels and 461 lbf.ft torque (about 580 bhp / 530 lbf.ft at the flywheel) ….. makes a good noise too, check the You Tube video
All the details about the engine along with build photos can be found on my Chevy LS6 page.
The suspension used on the car also has an American twist in that the uprights, hubs, wheels and brakes are from a Lola T8800 Indycar, Indycar being the American equivalent of Formula 1.
I designed the suspension geometry using my own suspension design software to give good roll centre and camber control. The car has rocker arm suspension with rising rate. Adjustable blade type roll bars are fitted front and rear as are adjustable Penske shock absorbers.
The wheels are 15″ diameter by 11″ wide at the front and 15″ diameter by 14.75″ wide at the rear. I have two sets of wheels one set fitted with slick tyres the others fitted with wet weather tyres.
The Gearbox is a Hewland DG300, a gearbox first used in Formula 1 and Formula 5000 in the 60’s and then later becoming the box to run at Le Mans. The gearbox is a ‘dog ring’ box with interchangeable gear ratios, it has 5 forward gears + reverse. Also fitted is a Salisbury limited slip differential set up to suite the car. I also have a range of gear ratios that allow me to set the ratios to suite different race circuits.
The car has been designed to create downforce which results in greater cornering speed.
The car has a number of aerodynamic features these are; Front Splitter which is the horizontal surface at the front of the car, Dive Vanes fitted to front bodywork on the sides, Front Venturi built into the underside of the front spoiler, air is fed into each venturi and then between the front wheels and the footwell before being vented out of the side panels through tunnels, Rear Venturi this starts behind the drivers seat and extends out of the rear of the car, again channeling air between the rear wheels and the gearbox, the pressure reduction acts along the whole underside of the car, Rear Wing which is fitted to the rear of the car which is a full width wing and flap.
A lot of development is required to get the most out of the aero package and it will be a focus of development.