Stroking an engine...

[Car-Nut]

What is it?

Fors and against ?

Answer in plain english for a non mechanic

[Moeregaard]

It's a method of increasing an engine's displacement by lengthening the distance the piston(s) travel inside the cylinder. It's done either by re-grinding the crankpin centers on the crankshaft, or by fitting a completely different crank having a longer stroke. Hot rodders have been doing this for years with American V-8s. Since the Jaguar XK has a 106-mm/4.17" stroke--very long by today's automotive standards-- it's pretty much at its limit for any major gains through stroking.

[Car-Nut]

Thanks Moe,

Does this therefore weaken the engine

[Moeregaard]

Longer-stroke engines have a theoretically lower rev limit than engines with shorter strokes. Long stroke engines have more reciprocating mass, longer connecting rods, and higher piston-travel rates (meters/km or feet/mile). The XK's connecting rods are 7.50 inches between centres--very long by today's standard. An advantage to a longer stroke is that torque can be generated at a lower RPM and throughout a wider range than with a shorter stroke. This is one reason a stock E-Type is so docile in traffic.

The main reason I've heard for the Xk's long stroke is that the engine was conceived at a time when horsepower was rated via the RAC, and the equation for determining this (and the subsequent road tax in the UK) was used bore size as a factor when computing output. Smaller bores resulted in lower taxes, so I'm told. Some of you guys in the UK can probably shed more light on this--or debunk this as myth!