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?
Rob
