XK PLUS EXTRA
Leaving Classic Motor Cars’ Bridgnorth premises and heading off to explore some of Shropshire’s prettiest B-roads, it’s immediately apparent how smooth the XK engine is. Period road-testers praised the standard 3.8 Mk2’s flexibility – the result of having an additional 25lb ft of torque over the 3.4-litre engine carried over from the MkI. CMC hasn’t dynotested 38 BUY, but conservatively estimates that it’s generating the same 240lb ft as a standard 3.8 Mk2, though Tim wouldn’t be surprised if the true figure was far in excess of that.
He explains: ‘ The engine that we tend to build for cars that don’t race or do track days is very torquey. It’s probably not massively powerful but feels so because it has so much torque.’
An opportunity to open the throttle on a wellsighted section of the A458 reinforces that feeling of impressive power. The XK engine spins freely, and while it doesn’t pin you to your seat (it’s far too refined for that), the rate at which the speedometer needle climbs around the dial is genuinely astonishing.
Tim explains: ‘In terms of Coombs modifications, this car has the higher compression ratio, it has the cylinder head work and it’s got the cold air vent – it draws air from the front of the car rather than drawing warm air from the engine compartment – plus the larger SU carburettors.’
The XK growls through its exhaust at high revs but there isn’t a hint of gruffness, mechanical harshness or pinking. And that sonorous engine note – very much central to that impression of immense power – is another Coombs addition.
Tim explains: ‘ The system differs from standard from the downpipe backwards. It just takes a slightly different route under the car, keeping the exhaust a lot straighter. The slightly bigger bore also means that it’s tuned for better gas flow out of the car.’
And yet, this example exhibits the usual Mk2 quality of being remarkably silent with the Laycock de Normanville overdrive engaged when cruising. Having a higher state of tune than a standard 3.8 Mk2 means that economy suffers, but it’s estimated that it will still manage 18mpg – a figure offset by that additional fuel tank.