variations betwen cars

[David Reilly]

Remeber, The Met specified 3.4-litre engines in the Police 'S'-types. Jaguar Engineering Schedule, ref. A.202, which is a supplement to the main ‘S’-type Engineering Schedule, ref. A.175, covers the variations made on ‘S’-type Police cars. It runs about 70 pages.
All ‘S’-type Police cars were delivered with 3.4 litre engines. The original design of the XK engine was as a 3.4 litre. At this capacity, it had thicker cylinder walls and was considered a more rugged engine for police work. There was also a belief that the lighter weight of the 3.4 more than made up for the 10 horsepower less than the 3.8 and gave the car better balance and handling. If there are any ’survivors’ today with a 3.8, it most likely had a change of motor and, if matching, a change of data plate, grill and boot badges. SUU 491F’s original engine had a brass tag mounted on it, showing the date of the last re-build with the specs of bearings, crank, etc. stamped into it.
The only factory ‘non-standard’ on the Police car engines was the fitting of a 43 amp LUCAS alternator instead of dynamo, but the electrical system was still positive earth. This was a requirement to meet the higher loads from the additional electrical equipment, radio, lights and bells, particularly when a police car was parked at idle.
Cheers,
David

[Jose]

so 10 horsepower is the difference between both displacements?

no wonder I perceived the 3.4 to be "sweeter", thicker cylinder walls is probably the reason.