Just go for the dual SU HD6 13/4 inch carbies on the 3.4 head. The original Solex 1 1/4 inch carbies really strangled the engine.
Using Pi R squared the SU HD6 carbies increase carbie inlet area by about 80%.
The increase in engine response and power has got to be experienced to be believed even on a small valve 2.4 engine.

Jaguar stated that with a straight port head, larger tailpipe as per 3.4/3.8 and SU carbies there was a 30 HP increase.
I reckon that I have got a 20+ HP increase just with the carbies and a larger exhaust pipe.
The stock HD6 carbies off a 3.4/3.8 don't need any tuning modifications.
The stock inlet plenum and air cleaner off a 3.4/3.8 engine will fit OK.

I have done this modification on a MK1 and MK2 2.4 cars.

 

Exactly Bill ~ as I state above that has got lost.

To my knowledge the Big Valve head (B head) would fit fine ~ but. Jaguar fitted it to later models (Mk2 ~ 2.4) & were not happy that the car would still not reliably reach 100 miles an hour hence the straight port head on the 240 which could genuinely do 100mph with SU HS6 Carbs & heated manifold. They thought the B head fitted to the Mk2 would make up the performance deficit & it didn't

The 340 with straight port head, which Jaguar kept quiet about, would clobber a 3.4 Mk2 or S Type and Autosport got it comfortably over 120mph on a two way run. (This did not suit Jaguar's strategy which is why they kept quiet about it when they did away with the 3.8 Mk2).
While cheapening in other areas like no Fograngers & Ambla upholstery both 240 & 340 gained in the engine stakes.


The Big Valve head (B head) 2.4 would not do 100 miles an hour. The 240 with straight port head would standard with ease.

"The more significant changes affected the 240, whose engine now boasted a power increase from the earlier 120bhp to 133bhp and a small torque increase from 144lb ft to 146lb ft at 3,700rpm. The main benefits of this were that the car could now exceed 100mph with ease for the first time and that its high-speed acceleration was improved." It was still not a bank robbers car but the 340 was.

Then stick a big bore dual exhaust on the thing as you suggest and you will get another performance rise out of the 2.4 engine. (340 has it already)

 

It's difficult comparing the different engine configurations as the changes were rarely made one at a time. I've seen it argued that the 2.4 was better with the B-type head and SUs, Bill's version, than the straight port with SUs, factory 240. For sure, the Solex carburettors strangled every version of the 2.4 engine they were fitted to. My own opinion is that the short stroke 2.4 (and 2.8) engines were never given the treatment they deserved. Their parts, carbs, cams, ..., were chosen for economy, fit something cheap/easy for assembly/same as the long stroke engines, rather than achieving best performance.

 

Well we need to get someone to do a comparison & with the big bore twin exhaust. That said ~ empirically the straight port head would seam to make more sense.

At least with the 340 Autosport did the two way run and proved their point ~ the next best thing to a dyno. If I was in the market for a Mk2, I would buy a 340 or a 3.8.

 

Definitely agree on the 340.

Two primary aspects of engine performance are filling the chamber and how the flame gets across the chamber. The port shapes are good and all the heads flow quite well (for the time and the original design displacement of around half a litre). Some help with flame propagation is desirable in the small displacement engine with its lower port velocities and the generally quiescent nature of the design. Extra swirl from angled ports or turbulence from a shorter inlet valve duration might well improve horsepower and torque.

 

Indeed they might or might not with Jaguar's previous experience Mk1 to Mk2 with the 2.4 & B Head. It performed poorly & went backwards if anything but there is weight & other factors to consider in that case.

 

The XK engines problem was it always breathed better than it burns, which is part of the reason they need lots of ignition advance compared to other engine designs. The hemi design isn't very good from a flame propagation point of view, and that was really accentuated on the short stroke 2.4 with more piston dwell time at TDC compared to a 3.8 or 4.2 version.

The ideal solution is a new combustion chamber design, but that's obviously not a practical or inexpensive thing to do.

 

Yes ~ piston speed was quite a bit lower with the 2.4 vs, other larger varieties.

Harry Weslake warned Lyons that the long stroke & high piston speeds were less than ideal. We all understand the tax implications but other designers did not let that get in the way. They just passed on the tax implication to the buyer. Weslake did not like the hemi design either. I guess head design was his greatest forte.

Anyway with the larger engines we all enjoy the low RPM torque. You can happily change up at 2700 RPM. One of the reasons I like my 3.8.

 

In many ways it's too bad they were not inspired by the Rolls Royce Merlin engine design, which was way ahead of it's time - pentroof combustion chamber with 4 valves and overhead cams, features Jaguar wouldn't adopt until the AJ6 engine in 1983.

 

Spot on JB! And they had high altitude to contend with. The Merlin was a masterpiece and RR kept improving it.

 

The last year of RAC tax was 1946 in the UK. Its influence on the design of the XK may have been indirect. Lyons rarely (if ever) invested in new production equipment. The XK was manufactured with secondhand machine tools bought from John Black of Standard. It's possible that set the bore spacing or, at least, the distance between the centre lines of cylinders 1 and 6. Lyons is often criticised for his parsimony, but he was probably already in debt to the bank at the end of WWII. And Jaguar survived better than Standard and Humber, the sources of most of his secondhand hardware.

Harry Westlake and Keith Duckworth are often given credit for four valve head design, but its history certainly goes further back with Henry's Peugeot, the Merlin (mentioned by JB) and designs by Bentley amongst others. Since the two valve hemi had worked well for pre-war Grand Prix cars, a four valve design probably seemed excessively complicated for a road car, though Hassan knew it well through his experience with Bentley. In fact, in spite of the XK's relative sophistication for it's time, one of Heynes' objectives was simplification.

 

That's why South African machined & assembled engines were considered superior to Browns Lane. They were machined on the latest & new state of the art equipment for the era paid for by the SA Taxpayer when our Phase 2 ~ 53% local content program was still by weight.

As you say the first motorcar in the world to have an engine with two overhead camshafts and four valves per cylinder was the 1912 Peugeot L76 Grand Prix race car designed by Ernest Henry and Yamaha debuted the world's first production five-valve per cylinder internal-combustion engine in 1984 with the FZ750. In 1979 you had Honda's OHC 8 valve per cylinder oval piston engine used in endurance racing. They produced an F1 version of that engine that the FIA promptly banned. The Italians were also into multi-valve per cylinder engines early on.

The multivalve concept did not come out of the UK

 

... and with 50-year old machine tools and various improvements, economies, and compromises to the design, we wonder why the later 4.2 block had a few problems and a shorter life expectancy than an old 3.4 or 3.8 engine from the 1950s or 1960s!

If I may be a little cynical: while R-R most often produced great triumphs of development (and testing) over design, Jaguar, up to the 1980s, often in their production vehicles gave us something that tended to the opposite, triumphs of design that never received the development they deserved.

 

The 4.2 block had more than a few problems IMHO of course.

https://www.jagtas.org.au/torque/tec...-engine-block/

 

Thanks for this. My take away as I head toward spring is that if I can find an intake manifold for a 3.4 and dual SU HD6 carbs, I will be able to fit all of this with air filters into the 2.4. I am headed to Glasgow Scotland in April to see my grand daughter. I might be able to track down what I will need there.

 

The head from a 3.8. (Mk2 or S type), probably more numerous in the US and widening the choice in the UK, is identical to that from the 3.4.

​​​​​It might make some interesting hand luggage on the flight home!

 

You have a head for a Mark 2 2.4? I am interested. What's the story on the head? In what shape is it? I have learned from this site and the good folks who have so much knowledge and are so helpful, that the redone 3.4 head that I have will fit but will need new carbs and intake manifold. It might be easier to get a good 2.4 head and put it on with the original intake manifold and carbs.

 

You definitely don't want the manifold with Solex carbs. It strangles the engine. Now a 240 straight port head with SU Carbs is a whole different & desireable move.

 

There is no difference between a MK2 2.4 and 3.4 head.
Only the MK1 head had small valves.
If you want to use the Solex carbies do so by all means. However, you will miss out on the improved performance of the SU carbies.

 

Check your baggage allowances if you intend to bring a cylinder head back with you. It might be overweight, depending on the airline. Unless the studs are removed, it will need to be crated, rather than just in a cardboard box. I had considered bringing an X300 cylinder head back and figured I couldn't do it. One thing to consider is I typically see more water passage corrosion in heads from the UK, as they can get away with water or weaker antifreeze in the UK's mild climate. I've never seen a Canadian engine with UK levels of internal corrosion simply because good antifreeze is a must.

Check with your airline, but usually 32kg ( 70lbs) is a hard upper limit to the weight a single piece can be. That is the dividing line between baggage and cargo. Also check maximum dimensions. The XK head isn't light, you might not be able to transport one as baggage.