XK in a Kit Car. Expertise Needed

Hello all.

I’m researching a kit car project that would need an XK 6 cylinder inline. I’m on a smaller budget, meaning I can’t drop 15K on a rebuild, but I do have some funds to at least do it reasonably proper and then update as the years go on.

I would want to run the XK on the triple Weber setup and not a stock or aftermarket fuel injection. I don’t need to be historically accurate, so the liter size is flexible. I just need the XK6 block that was used up until the late 80s or early 90s. Also, the vision for this vehicle is a sunny day country road cruiser with some pep, not a track day racer or a high HP street machine.

Also, because I am an amputee, I am restricted to an automatic transmission. I would prefer an overdrive setup, but that’s not a deal breaker.

So some questions…

What XK block years should I avoid? I’ve heard of later ones having cracking issues. Are there certain years that are more reliable than others?

Can a XK engine that left the factory with fuel injection be converted to carburetors without any internal engine modifications? If not, what is the last year the XK was made with carburetors?

What is the smallest automatic transmission (overdrive preferred) that can be adapted to work with an XK? I know there’s a reliable kit for the GM 700R4. Anything out there for a Ford AOD? Or perhaps something from Toyota? Reliability and simplicity is the goal, so something like the Ford AODE isn’t desired.

Lot of info. Thank you for your patience. I hope this made sense.

Greetings All,

You ask the best block to use but then want to use the late 80’s early 90’s block.

Personally, the 3.8 is a better choice as it is a “dry liner” engine that had far less issues with cooling and hot spots.

Dump the Webers, since the cost is far more and you’ll need to dial them in which will necessitate you paying someone unless you plan to do the work yourself. Plus YOU said it wasn’t important and thats a lot of money for something that is not important.

SU’s have 4 moving parts and they flow better than Webers.

Look into BowTie Overdrives for one of their automatics 700R4 GM unit.

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Doug, you definitely want to go with a 4.2 block, more readily available and therefore cheaper to purchase. It’s a dry liner block, same as the 3.8, comes std. with a straight port head.
All 4.2 blocks have a tendency to crack if over heated, but other wise are extremely reliable.
I ran a 4.2 E race car without any problems back in the early 90’s, great engine, made 350HP @ 7500rpm.
A set of webers with manifold and linkage but without air cleaners will cost around $2300, add the air cleaners and a dyno tune, approx another $1000.
If you go with an injected engine, you can get a stand alone ECU kit for less than $1200.
For Auto’s you have a good choice, 200R4, 700R4, or AOD. All require an adapter plate.
The 200R4 is the lightest of the three, and was used behind GM’s 305, both the 700R4 and AOD behind 350/351 engines.
The 200R4 and AOD have a 2.76 !st. gear and the 700R4 has a 3.04 !st. gear, all of which are lower than the original Jaguar BW65/66 at 2.46.
I have a 200R4 behind a 455 in my 1965 Buick Gran Sport, that was built with HD components to handle the Torque of this engine.
If you are on a Budget, then you’ll have to do your homework to achieve your best outcome.
Good luck.

Hi Doug,
Welcome to THE Forum.
What Kit are you building ?

The classic Jaguar twin cam inline six was produced from 1949 to 1986. The late eighties, early 90’s, time frame you inquired about would not be the XK engine, but the XJ40 engine, which is quite different. Are you perhaps confused about which engine family you require?

Thanks for the great responses. I’m still learning all about Jaguars. I have a 57 Chevy and drove a 60 Cadillac for years beforehand, so I’m certainly more schooled in GM. I’ve been wanting to get out of my ‘comfort zone’ a bit, and I’ve been intrigued by the beauty of 50s and 60s Jaguar cars for years.

I’m planning on building a replica kit of the 1957 D-Type. While it’s not going to be a show car, I wanted to try to make it as much of a Jaguar as possible. My goal would be to get it on the road sooner rather than later, and since it would be something I would never sell, I have no problem with initially installing a less desirable but more budget friendly motor since I can always pull it myself in a few years to swap or upgrade it. Depending on how things go at the start, I might even just stick a Ford 4 cylinder inline with an AOD and run that for a year or two until I can collect and create an ideal XK inline 6 setup that does the car proud. Bottom line, I want to drive it, not have it sit in pieces in my garage for a few years while I find the perfect engine.

I don’t ‘want’ to use the late 80s early 90s block per se, I was just assuming that a later year block would be cheaper and easier to locate, thus I was leaning towards a 4.2 unless it was recommended that I avoid that decade. I agree that the Webber may not be the best choice out of the gate. The SUs look like something I could grasp easily. I enjoy reliable simplicity.

I’m not necessarily shying away from fuel injection, especially if it’s already on the block that I happen to acquire. I’m just worried about the programming complexity even with a standalone ECU, and it might not fit in the kit car with the EFI attached. I’m guessing that no one makes a standalone EFI kit that would work on a carbed XK? They’ve been making them for a few years for Ford and Chevy V8s and they just bolt onto the existing manifold.

As for the time frame, I was under the impression that they were using the XK in the Daimler Limousine until 1992, which is why I said ‘late 80s early 90s’. I could be wrong on that.

This info certainly gives me avenues to explore. One question I didn’t see an answer for … Would a later model block that comes with factory EFI run fine with carburetors? Or would internal changes have to be made to the engine?

The internals would be compatible with either EFI or carbs.

Used CJ6s, up to '86, can be had for a song, and represent the highest level of development of the XK engine.

I’d steer clear of Weberizing it, unless you have access to a chassis dyno, and someone who knows how to set them ya.

A dual ZS, or SU manifold will getcha on the road cheaper and nearly as fast.

I am “lumping” a '66 Jeepster with a SIII J6 engine, plus its complete EFI system.

Sold of course into 1992 with the DS420… I‘d get an 80‘s 4.2 XJ block and use the aforementioned carbs. They bolt on.
The EFI needs the manifold, metering and computer as well as plumbing for the fuel return.

What country are you located in? That will have a great impact on what is commonly available in your area.

Greetings All,

Since when is the 4.2 XK a dry liner block?

If you are in North America, you will have a higher probability of being struck by lightning than finding a Daimler of any model.


Well, here is my personal preference. I would stick to engines built from the early 1960’s to the late 70’s. 3.4L blocks are the most bullet proof. No liners, dry deck, not much to go adrift. 3.8 blocks are linered and can suffer cracks between the liners. Someone can correct me, but I believe that mid sixties 3.4 &. 3.8 crankshafts are the same part number and slightly beefier than those of the 1950’s era.

4.2L engines are a more complicated family. Early blocks are dry decked, but on later blocks, S3 XJ6 for certain, the head studs extend all the way through the water jacket to the block skirt. If the engine was well maintained, always used an antifreeze with corrosion inhibitors, this is not a problem. If the car was run on straight water as a coolant, it is very common for the heads studs to corrode to the point that they fracture. Often they will do that when you try to remove them to check for corrosion.

I would stick to manual choke carbs. Simple, effective, less to go wrong. If you decide to do Webers, you will need to employ the services of a brilliant tuner. The good news is that Webers are infinitely adjustable. The bad news is that they are infinitely adjustable. Aftermarket fuel injection, where you can view the performance and mixture in real time on a laptop, is 10 times easier to tune.
If I were doing fuel injection on a kit car, where the appearance mattered, I would use an aftermarket injection setup.

Also, mid sixties stuff tends to be much more nicely finished than the 1980’s stuff produced under the BMC ownership.

All that said, here is what I have done. This engine was built to comply with the vintage racing rules in affect when it was built, so the displacement had to be 3.4L and I was restricted to two carburetors. 3.4L block and crank from a 1964 Mk2, straight port cylinder head from a 420, intake manifold from a 4.2L North American S2 E-type, twin 2" C-type SU H8 carbs, magneto ignition. Crower billet steel rods, Arias pistons. Will reliability spin to 7,000 rpm.


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Always AFAIK.
The only contact the liner has with the coolant are slits cut into the top of the bore.

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Paul, did you mean a Jeep CJ6? Or did you mean XJ6 but had a typo?

He meant XJ6 pretty sure…
Despite the „jeepster“ later in the post!

ALL 3.8 and 4.2 blocks are dry linered. And as far as cracks between the bores, this is not a detriment, as in the late blocks, the Factory actually machined a slot between the cylinders, which proved that “stepped liners are a waste of money.
If you do have a cracked block and have any doughts on it being a problem, you can use a “Loctite” product called “Wickin” that will seal the crack(s).
The later “long stud” block was introduced to reduce stress in the top deck to reduce the chance of cracking.
The 3.8 crank is different than a 3.4 as it has more counter weights for a better balanced crank. This also applies to the 4.2 crank.
The “old wives tale” that the 3.8 is a sweeter engine than the 4.2 is the result of the 3.8 being a better “quality control” build, which if the 4.2 was built the same, there would be no difference.
A lot of after market EFI systems these days are " self tuning” once you have set the basic paramatures.
Here in Australia, FORD produced a 4.0L Falcon with a “self tuning” ECU that adapts quite well to the 4.2 Jaguar engine.

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Mike, 3.8 cranks have more counter weights for better bearing loads at high rpm.
I built my 4.2 Race Engine with S3 rods (much lighter and stronger AND cheaper than Billet) fitted with ARP rod bolts.
Made 350 HP @7500rpm. and would rev to 8000 all day.

XJ6: I often use the shorthand, ‘J6.’

My hot rod that it’s going into is a 1966 Jeepster

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