3.0 litre race XK over bored 2.4

Hi gang.
Jaguar and maybe some privateers produced some 3.0 litre XKs for racing in appropriate classes c. 1960. There was an all alloy block one produced for the E2A built for Briggs Cunningham, that was 85mm x 88mm, producing 295 bhp at 6,800 rpm on Lucas injection and presumably wild cams and high comp pistons.

I have seen a passing ref to a presumably iron blocked version with standard 83mm bore & 92mm stroke.

No info found on whether these were based on standard 11.5" blocks or the lowered 8.85" 2.4 one, but possibly theoretically possible with either. (Horrid 2.8 had 86mm stroke) The short block one would have shorter con-rods, so less chance of whip at high revs.

Anyone with further info?

Since it is known that racers were boring out 3.8s to 4.2 before Jag introduced revised spacing 4.2 block, it should be possible to take 2.4 block with same bore spacings, using liners, out to 91mm bore to give 2985cc, with 76.5mm stroke to give a high revving screamer, as per modern oversquare engines.

It seems 2.4 had same main and big-end journal sizes as bigger lumps, so should take similar power and have less revolving mass, enabling higher revs and easier balancing.

All heads will fit 2.4 block, inc later 4.2 straight port, wide angle. Last 240s had this head as standard, but valves considered too big for road spec, but which is fine for tuning!

The problem for tuned use is to get a decent comp ratio with short stroke, without a huge dome to impede flame travel. Anyone know the maximum that can be machined from head face?

With 2.4 lumps being largely unwanted, it could be a cheap way to enter sub 3 litre historic classes, or in the UK, sub 2.7 litre for pre-1966 cars. This capacity can be achieved with 3.8 87mm pistons and cut down liners, with any regrinding of the crank big ends being offset to reduce stroke 1mm to 75.5mm for 2693cc.

The biggest question of all is – Why didn’t Jag do the same?


Maybe they did !!
I know they tried a 4 pot !

Great pic, which accentuates just how tall XK engine is.

I’ve since read that some folk have taken 2.8 out to 3 litre using high comp Toyota pistons.


Ultimately it comes down to the lack of a big enough market.
A high revving big bore short stroke engine in a luxury saloon was not their market.
The sports market was pretty well serviced by their 3.8 Litre.
BTW the 4 cylinder 2 Litre in the picture was contemplated for what eventually became the Mark 1, but it suffered from a second order vibration inherent in large twin cam engines, which they could not solve, and meant it would not be desirable in the small luxury saloon.
A few decades later Porsche and Volvo solved the vibration problem with two counter-rotating balance shafts at the crankshaft level.

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It was competition engines I was talking about. 3 litre XKs said to be used for some sub 3 litre classes, in D & E types, E2A, Listers, HWM, Cooper & Tojeiro. A Mk 2 with sorted short stroke lump in a 3L class could approach power of a 3.4, yet get more class wins!

I read in a Daimler forum recently that someone has taken a 2.4 out to 3L, but no details.

Lanchester had counter-balancers pre WW2.


Did anyone ever figure out if this can be done? I was gifted a 2.4 L motor that I’m now building a Tojeiro replica around, and was thinking about increasing the displacement of the motor. I’m also wondering if anyone figured out if there was a piston that could be used from another source.

Ron Beaty used to bore out 2.8 litre XJ engines to 3 litres (or a bit more). The 2.8 was essentially a longer stroke 2.4 made for some European markets to get under a tax break.

Virtually anything significant you can do to increase displacement from 2.4 will cost more than just buying any other 3.4, 3.8 or 4.2 XK engine. The advantage of the 2.4 is that it is significantly shorter than the others, so it can fit where others fail.

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The 2.8 is the same.
What pistons would fit a 2.8 → 3L?

The reasons I have for sticking with the 2.4 is: a) it was free (though it’s now cost way too much money b)it’s smaller and slightly lighter, c)bored to 3L would be historically accurate, and d) this motor has some sentimental value to both myself and my friend who gave it to me.

I know the easy button is going to a 4.2 from an XJ6, but I like to do things the hard way.


Needs it’s own post. Please put up some pictures of the progress on your Tojeiro build.

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Going from 2.8 to 3.0 isn’t an enormous over bore. Over size pistons were probably around back in the day. Someone might have some old stock?

Some of the 3.0 engines made for racing in the late 1950s were tall blocks with a shorter stroke crank and standard con rods. They used tall pistons to compensate. This may have been the cause of the piston problems they had.