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Mclaren 650S Limited Slip Differential.

Problem
Out of the factory the McLaren 650S uses an open differential with a relative ‘long’ final drive
ratio. For race and hill climb purposes, a limited slip differential for maximum traction in
combination with a shorter final drive ratio is desired.

Solution
Find the ideal final drive ratio in combination with an LSD for Hill climbing keeping the car
suitable for road racing within a time frame.

Description
A project starts with a clear view of the customer requirements. These customer needs are
required for making the correct action plan and design choices.

For this project the following project structure has been followed:
1. Mapping customer requirements
2. Dis-assembling gearbox
3. Reverse engineering CWP(Crown wheel pinion) set and original differential
4. Determining best final drive ratio and LSD setup
5. Strength calculations
6. Evaluation design choices with the customer
7. Creating final designs in 3D
8. Production
9. Testing and validation

In this case the customer wants to do competitive racing. So reliability is an important
factor in this project. Without any modifications the Mclaren 650S is able to reach a top
speed of around 330 km/h. For Hill climbing lower top speeds are required than for circuit
racing. To keep the car suitable for circuit racing, a top speed around 275 km/h needs to be
achieved.

To start off the project, the original gearbox needed to be dis-assembled, producing special
removal tools on the fly where desired. After that the reverse engineering could start with the
results out of the 3D measurements. Desired strength calculations had to be performed
including the specific tooth shape calculations of the CWP set. Determining with use of the
gearbox ratio diagrams, we found an ideal final drive ratio around i=4.00 to meet all
requirements. After choosing the best LSD setup and verification with the customer, all parts
had a go for production. Crown wheel, pinion, LSD housing with all the internals and relevant
accessories were produced resulting in high quality parts ready for racing!

Case slideshow

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