3.0 litre race XK over bored 2.4

(Rob Maxtone-Graham) #1

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?


(Ian) #2

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

(Rob Maxtone-Graham) #3

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.


(Rob Reilly) #4

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.

(Rob Maxtone-Graham) #5

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.