Automobile Engineering in ME
The condition that causes vapour locking in a brake system is

Keeping the vehicle without use for an extended period
Overheating of the fluid due to frequent brake application
An excessively high engine speed on a downhill road
Overcooling of the brakes during high speed driving

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Automobile Engineering in ME
The compression ratio in petrol engine is kept less than in Diesel engine because

Higher or equivalent compression ratio in petrol engines is not possible due to pre-ignition
It is just customary to have less compression ratio in petrol engines
It makes petrol engines lighter
Less compression ratio gives better performance

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