Hi all! This is my first post on this forum, excited to have joined. This lockdown, I’ve bought a fairly tidy mk2 2.4 for little money from a film company’s inventory. It was a really nice project to get it running better, service and fix things, clean it up, style it a bit and drive it around. It’s a lovely thing!

With a stock 2.4 engine with Solex carbs, it’s not particularly fast. Being aware of its limitations, I was wondering to what extend more minor modifications could be undertaken to make the car a bit more lively.

Three initial ideas (before going too crazy!):

• does it make sense to upgrade from the stock Solex carbs and intake? For reasonable money I could buy a 3.4 B head intake manifold, and a pair of 1 3/4” SU HD6 carbs. Does this make a difference over Solexes?
• would a Jaguar 240 dual exhaust system fit, or be made to fit? Having two pipes would probably enable the engine to breathe a bit better (and it’ll look nicer)
• in my experience, electronic ignition is a nice upgrade for any vintage car. Any experiences adding this to a 2.4, or any mk2?

Looking forward to hearing from you all! Regards Adriaan (Surrey, UK)

 

Courtesy of James Taylor ~ The usefull changes made to the 240 version of the 2.4 litre XK engine:

"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. The heart of these improvements lay in the straight-port cylinder head of the [similar to is what he actually means] 4.2-litre E-type engine that had replaced the old B-type cylinder head. [you can't use a 4.2 straight port head]. However, the 240 engine also had a new water-heated inlet manifold, which carried two SU HS6 carburettors in place of the Solexes on earlier 2.4-litre engines. A paper-element air cleaner with twin intake trumpets replaced the old oil-bath type, and a new dual-pipe exhaust system made the most of all these changes."

Best to search out some 240 parts. Head, manifold, SU's & dual exhaust. The 240 head was also fitted with ribbed cam covers. When rebuilding a 240 straight port head I would also have it ported/gas flowed by a pro on a flow bench that will further improve power. A custom exhaust manifold would also improve matters.

 

Thanks for that. Sounds like the dual exhaust system of a 240 should fit to the 2.4 exhaust manifolds; might need some custom brackets. Challenge might be the straight port head; these are now fairly expensive. A manifold and carbs for the b-type head are available here for c. £200; I can refurbish most of it myself over the winter. I’ve unfortunately seen knackered straight port heads for £1k, hence trying to work with the original B head. Can these be made to flow better?

 

Are those 2.4 straight port heads or E Type, MkX/420G triple carb straight port heads?

Yes a B type head & inlet manifold can be gas flowed ~ possible gains unknown. I also suspect that the standard exhaust manifolds could be improved on. You can also bump the compression up a bit.

Eagle tuned exhaust manifold example.

 

I was under the impression that while the straight port head allowed the engine to make more total power, it moved that power up the rev band, and low end torque actually went down.

A single exhaust should make more lower rev band torque at the expense of higher rev power. You need to decide what is important to you and build the engine accordingly.

 

About electronic ignition, Pertronix needs shielding to work properly IMO, it's a magnetic switch, I've read a few articles where the spark jumping from the rotor to the cap can and does effect the proper functioning of the Pertronix unit.

I'm considering a 123 ignition for my Bentley to get rid of the finicky duel points.
The 123 ignition gets rid of the mechanical advance weights and vacuum unit as well.

Check this video out, the Pertronix part of the video isn't much better then the points.
The clearer the "123" that shows up on the strobe wheel, the better the system.

 

Thanks guys, that's helpful. The last couple of months I've been setting up the Solexes as good as possible, and with servicing the car thoroughly, playing with tyres and road set-up, and the odd 'Italian tune-up' on a Sunday morning, it has come to life a bit more and is turned into an enjoyable drive. I think another 15 horses combined with some more exciting intake/exhaust noise could liven things up a bit though.

It sounds that a combination of the new SU HD6 carbs + manifold, a dual exhaust system from a 240 (or potentially done by an independent shop) and a 123 programmable ignition would be a nice place to start without breaking the bank. Good point re the ignition system; indeed very helpful for any (future) mods to keep that flexible and reliable.

Am fully aware that the gains might be limited, but I think the process sometimes is just as much part of the enjoyment as the end result, therefore keeping modifications in the 'reasonable' category cost-wise. Happy to hear any other suggestions how to improve it further as a drivers car!

 

You can also use a Series III XJS distributor and amplifier for a cheap path to electronic ignition. There are various combinations of weights and vacuum advance that you can use from various years to get the advance curve close to what you want.

Or if you want to do something else just for the sake of doing it, there is Megajolt. It lets you go distributorless and full programmable. I have done that in combination with Megasquirt, which is fuel injection plus ignition.

 

An engine is an air pump. Tuned length inlets & their unrestricted flow increases volumetric efficiency. Tuned length, diameter & flowed exhaust manifolds & pipes improve scavenging of exhaust gases.

Both will increase horsepower & frequently broaden the the torque curve. Some tuning choices can push both up the rev range & many down the rev range. It's a matter of choices made by tuners. Both are dependent on Pressure Wave Propagation & flow.

Valve sizes, camshafts, valve overlap etc. & many other considerations also effect this.

The subject is vast & there are many fine papers on the internet that cover the matter in detail. Trying to cover it here is futile.

So one either goes to a tuning pro on XK engines or stick to known parts & their measured output. The OP's intention is a moderate increase in power inexpensively.

e.g. Ian Callums 4.3 litre XK engine in his Mk2 was specifically tuned for low end torque. One can read all about that on the internet as well.

In the case of the 2.4 engine vs 240 straight port head engine. Torque: the original 2.4 produces peak torque at 3000 RPM wheres the 240 engine at 3700 RPM. Power: 2.4 engine peak bhp at 5750 RPM & 240 straight port head engine at 5500 rpm. So 240 more power at lower RPM & more torque at higher RPM.

 

If I'm remebering correctly, the 240 has a milder cam than a 3.4 or 3.8 in an effort to boost lower rpm torque. Jaguar was never happy with the specific output of the 2.4 engine.

 

Adriaan you may wish to secure a copy of Jaguar publication E/112. Jaguar offered this tuning booklet which fully describes the 3 stages of tuning and all associated parts necessary. It would be a great start at not re-inventing the wheel but of course they were limited to tech. of the day.

 

The 2.4 was always a disappointment & underdeveloped by Jag. It was however a silky smooth & pleasant power plant. It certainly had different cams to all the rest of the range. Whether the difference was in max lift or profile or both I have never bothered to check. Smaller bore 6's always have issues with max valve size. Above I'm talking standard cars as sold in the Mk2/240 range.

I agree with Coventry Foundation above. These kits were made available for the Mk1 2.4

Basically: "The tuning kits came in three stages, each one making a worthwhile difference to top-end performance but – as Jaguar warned – also having an adverse effect on acceleration at low speeds. The Stage I kit boosted power from the standard 112bhp at 5,750rpm to 119bhp at 5,800rpm and consisted essentially of modifications to the carburettors and the exhaust. Stage II took power up to 131bhp at 5,900rpm and brought high-lift camshafts, stronger valve springs and a new distributor in addition to the Stage I changes. Stage III delivered 150bhp at 6,000rpm by replacing the cylinder head with the new big-valve B-type head that was fitted to the 3.4-litre engine in the XK140 models. [note this was a 2.4 version of the head]. With the new head came two SU HD6 carburettors and a twin-pipe exhaust system. Jaguar also recommended fitting (at extra cost) uprated clutch [pressure plate] springs to cope with the increased torque of the Stage III conversion."

Detail in E/112.

Availability of some parts unknown. This obviously with conventional tuning wisdom at the time. In modern engines these things can be accommodated by variable lift cams, variable valve timing, variable length inlet manifolds etc. etc. Good knock sensing & continuously variable timing by the ECU etc. Dependent on the onset of knock.

 

The 123 Ignition system is excellent. However the main purpose of the Pertronix Ignitor is to have cheap pointless ignition with their high output coils so that one does not have to worry about point burn & gap change & endlessly worrying about dwell angle as a result. The PI is a lot better than burnt, incorrectly gapped points as their cam follower wears. Removes a PIA service item. Especially on classic Jag saloons with their awful distributor access. Nothing wrong with hall effect switching.

 

I still have points in my Jag, I don't even try and change them in situ, I set number one on compression with the correct timing mark lined and and remove the distributor.
It's way easier to simply retime the ignition then it is to fiddle with the tiny washer and nut, let alone to set the gap.