To get things into context you must remember that Sir William Lyons was attempting to break into the domestic sales area of the UK market when he first came up with the small 2.4 saloon which subsequently became known as the Mark 1.
At the time the Mark 7 was in production however it was viewed by the British as a large car. In fact the Mark 7 was aimed squarely at the export market as steel supplies in Britain were still rationed under a quota system. You could only get steel if you were in the export trade.
Sir William was no slouch in recognising that he needed a car which would be acceptable to the home market as being reasonably economical, fast and still be of a size easy to manoeuvre and park in the congested streets of that island continent. He also had to consider that in the UK domestic economy petrol was very expensive. Petrol rationing had only ceased in 1952 and nearly returned in 1956 during the Suez crisis.
It should be noted that in 1955 when Sir William introduced his MK 1 Australia was involved in a love affair with the FJ Holden which only ceased production in late 1956 It’s replacement which was the FE/FC series Holden was no faster. Sir William gave the world a twin overhead cam vehicle producing 112 Horsepower out of 2.4 litres or approximately 144 cubic inches, which did 100 miles per hour and easily did 100,000 miles without any overhaul. What General Motors sold to Australia was a vehicle called an FJ Holden with approximately the same capacity in a pre war pushrod GMH engine design that produced 60 HP, did 83 MPH and had a life of 50,000 miles between overhauls if you ignored the gudgeon rattle which started at 20,000 miles. In those terms alone the 2.4 Jaguar was no slouch. You could not compare the brakes and handling. The Jaguar was so far in front that it is like comparing a T model Ford to a post world war 2 car.
Anyone who has owned a 1950s British car will understand that the British paid slavish attention to fuel economy. The MK1 2.4 was no exception. It had a deplorable pair of Stromberg downdraft carburettors to miserly feed the fuel into the engine and a whimsical narrow tailpipe/exhaust system to get rid of the gasses. The early model also had very small valves. After all that, it is remarkable that the car did so well as to make 100 MPH. Some British reports claimed an economy of 26 MPG however in practice 22 to 23 MPG from a MK 2.4 is more realistic. By the way the MK1 2.4 was officially about 2MPH faster than the MK2.
Many 2.4 Jaguars imported into Australia are also saddled with automatic gearboxes, which further reduce performance. The old DG [Detroit Gear] series box, which is really, a Borg Warner 35 series in disguise does a good job but is very wasteful in power. They are also notorious for developing oil leaks.
What Are They Worth? Currently 2.4 litre sedans are very cheap and even an excellent example only brings a fraction of the value of a 3.4 or 3.8 litre car. I note that The Australian Jaguar magazine [edition 91] quotes
MK1 2.4 $1000 to $20,000 MK1 3.4 $1000 to $25,000
MK2 2.4 $ 2000 to $20,000 MK2 3.4 $3000 to $30,000 [3.8 $3000 to $40,000+]
The April edition of Australian Classic Car is a little more circumspect in quoting top price for a MK1 2.4 as $11,500 and a MK2 2.4 as $14,000 while the top price quoted for a MK2 3.8 is $29,000.
Better Brakes? Having faced up to the fact that a 2.4 litre sedan will never be worth as much as a 3.8 you still have a number of options if you feel that you want more performance. However before we go down that route there is one important aspect to remember particularly if you are dealing with MK1 sedans. It is no use making it go faster if you can’t make it stop. The drum brakes on a 2.4 sedan are “adequate” but on the MK1 3.4 are generally acknowledged as being at or even getting beyond their limits. If you are going to increase power then you should give serious attention to the brakes. There are kits available to install later series Jaguar disc brakes to the front of a MK 1 and I recommend you get in contact with suppliers such as Geoff Widdicombe , GBC, Jag World, British Cat Components and Don Milliner all of whom advertise in this magazine for advise, expertise and general cost of this conversion.
Heart Transplants Some of your power options include an engine heart transplant. If you can access a MK1/2 3.4 or 3.8 engine this is a simple and relatively cheap way to go. Unless the chosen transplant engine has really major problems you should be able to fully overhaul it for somewhere around $2000 to $3,000. If you are a do it yourself person you may get out of it much more cheaply. 4.2 motors are quite plentiful however you may have problems in sorting out engine mounts pulleys and other accessories.
I note what looks like a late model [4 litre?] fuel injected engine under the bonnet of a MK 2 in edition 91 [page 69] of Australian Jaguar. I also knew of a MK 1 with a Holden 179 engine, which lived in inner city Brisbane and regularly towed a trailer to the family weekend farm. Jaguar also put a V8 Daimler engine into the MK 2 body shell and called it a Daimler 250. From that point of view your options are pretty open.
Staying with the 2.4 and originality. A relatively cheap way to go is to look at the upgrades available on the 2.4 engine. Jaguar did offer a number of options in both manufacture and aftermarket products so you could make a number of improvements and modifications and still be “original”. It is worthwhile noting that Jaguar quotes the following HP figures of MK1/112 hp: MK2/120hp and 240 saloon/133hp. The 240 was fitted with the 13/4 SU carbys.
If you have one of the very early 2.4 engines it has small valves and as such the head is hopeless for any upgrade in power. A “B” series head with the larger valves and higher lift camshafts is needed. These are amazingly plentiful once you start looking as the majority of later 3.4 motors had them. Experts talk about “C” and “D” heads but they are rare, expensive and probably an overkill on a 2.4 engine.
Along with the B series head a MK1 or MK 2 3.4 intake manifold and SU HD 6 1 ¾ inch carburettors along with the starting carby are needed. These should preferably come off a MK1/2 3.4 or 3.8 engine. That will allow you to use standard plumbing for the cooling system and standard carby linkages. Another possible source is the S type sedan. The original 3.4/3.8 engines used a thermostat to control the starting carby. Most owners have modified them with a switch under or in the dash panel to allow direct control of the starting carby. One cunning place to fit such a switch is a push off/pull on switch fitted in the bracket just above the bonnet release knob and operating in a parallel direction with the knob. Somebody had done this to my MK 1 “hotrod” and you cannot see it or find it without being in the “know”.
Finally the crummy little narrow single pipe exhaust system used on the 2.4 should be replaced with the 3.4/3.8 dual exhaust system or at least a much-enlarged single pipe system. Note that the 2.4 exhaust system will not fit a 3.4/3.8 engine, as the increased height from below the vehicle to the exhaust manifold becomes a problem. There is about a 2 to 3 inches difference in pipe length due to the deeper motor, higher block and increased depth to get below the vehicle floor.
Jaguar also recommended 9:1 pistons. In view of the current environmental lobby and phase out of leaded petrol this may not be the best way to go. 8:1 seems to be about the limit for compression ratio with modern fuels and old engines.
With all of the above modifications including the 9:1 pistons it is suggested that an overall increase of about 45 Hp was possible. This would put the modified 2.4 engine at about 157hp which is pretty much the same as the original 3.4 engines rating of 160 hp as fitted to the XK 120 and MK7 sedan. Even without the higher compression pistons 20 to 30 HP should be achievable and would make a significant improvement to the performance of a 2.4 saloon.
Cooling the engine. I have had queries as to whether the 2.4 radiator would need modifying. As yet I have not been able to establish any difference between 2.4 and 3.4 radiators. I would suggest that if you have a marginal 2.4 engine that tends to overheat you would have problems if you did anything to increase performance. It would be best to have the radiator cleaned at least. John McDonald from Stafford Radiator Service who advertise in this magazine assures me that standard cores are readily available and special high capacity cores can be ordered for cars with specific problems such as air-conditioning added on etc.
If you have an early MK1 2.4 with a cast alloy four blade fan remove it and replace it with a late model MK 2 multiblade fan. The 4-blade fan is hopeless in the Qld. environment even when the engine and radiator are in perfect order.
Getting rid of the Slushbox [Automatic Gearbox] As previously mentioned the DG automatic gearbox is does waste a significant amount of power and ultimate performance will only be gained by replacing it with a manual gearbox. This is serious stuff as there are numerous areas that need to be addressed in such a conversion. [Been there - done that]
The simplest approach is to get a MK1/2 manual [moss] box and bell housing. However an engine previously used in an automatic car will need a flywheel and clutch plates. A slave cylinder, a different [single piece] tailshaft as well as a manual pedal box setup with clutch master cylinder and flexible lines will also be required.
There are also a number of other Jaguar manual boxes available however the gear lever position might take some working out as well as gearbox mounts. Don’t forget or overlook other conversions such as the 5 speed Toyota Celica box conversion developed by Ron Moore.
Differential ratios I refuse to enter this minefield. There are undoubtedly experts out there who may be able to assist. Limited slip differentials and their ilk sound great and have their uses but I think you need specialist expertise to get involved in those areas. If you have a diff that works OK for you then leave it alone. If you need some better ratios after a heart transplant the find out what original type was fitted to a 3.4 or 3.8 vehicle and use that as a starting point.