I have an chance to pick a 1973 XJ6 with the old engine with SU Carbs. It is a right hand drive car, and I was under the impression that he engines were 2.8 instead of 4.2. Were these cars delivered with the 4.2 engine? If so, how can I tell? thanks, need to know soon, as I will look at the car in a couple days,
The engine could be either 2.8. 3.4 or 4.2 not sure where you are but the smaller engines were made to suit the French registration regulations and were not normally exported to the USA.
The 4.2 should have 2 x 2” SU
3.4 would have 2 x 1 3/4” SU
Not sure what the 2.8 would have regarding the Carburettor size
If it’s a 4.2 litre it will have exactly that cast into the RHS of the cylinder block - right below the carbs. If you can’t get that close Robin’s post will be helpful. If you can post a picture we can tell you. Paul
jagster,
Jaguar cast the engine displacement into the right side of the XK engine block. Sometimes it is a bit difficult to see with the engine in the car but it is there. Attached are pictures of a 4.2L XK engine that I built up last year on my engine test stand to tranplant into my 1984 XJ6 Vanden Plas with the displacement circled in red and the 3.4L XK engine that I am working on now for my 1957 MK VIII where I highlighted the displacement in gold paint. If you can get a picture of the right side of the block there should be no question about the original displacement.
Paul
A quick visual check. re a 2.8 is the separate header tank mounted on the crossmember over the radiator, other than that is the lower height of the engine. Both series 1 2.8 and 4.2 are fitted with 2” carbs, early models HD and later HS
As the car in question is a 73 it will not have a 3.4 engine, at least if in standard spec, 3.4s replacing the 2.8 in the series 2 models.
Chassis number might give clue if it is the original engine . 2.8 prefix is 1G, 4.2 is 1L.
Engine nos for 2.8 prefix 7G, 4.2 is 7L. Another (obscure) clue is check the tag on the rear of the differential housing . It will have something like 13\39, indicating diff ratio, 2.8s had low 4.27 or 4.55 ratios, 4.2s had 3.54 or 3.31.
And of course the 4.2 has a much lower redline - beginning at 5000 rpm, the 2.8 going much higher. Both engines are nice, is the conclusion I reached.
The chance of it being a 2.8 is pretty low, and especially so for an automatic.
What is the factory redline of a 2.4/2.8?
I wish to thank all of you who responded to this request for information on the Jaguar engine displacement question. I was surprised to find a RHD car over here in the USA, as it would have had to come in with someone who had been across the pond I do hope it is a 4.2, as I have just about landed an E-type with a blown engine. The ‘E’ is a 1968 model and we were heavily into the pollution equipment by then. The ‘new’ engine looks to have a pair of SU8’s, and that will be an improvement over the Zenith/Strombergs. Again, my thanks for the help and advice. Ron Stephenon
Either 6000 or 6250.
Many say the Strombergs are very close to the SU when the secondary butterflies are disabled. So, you want a donor car then? Get an 8L (Series 3 XJ) block. They are far better, and easily obtainable without parts car.
The engine on my 1967 Mark 2 3.4 also says ’ 3 1/2 litre.’ I never did understand why they added a tenth of a litre. When I bought the car 31 years ago knowing it needed an engine rebuild, the mechanic said the cylinder walls were scored badly, so he had them rebored and put in oversize pistons, so he told me the engine was now probably closer to the 3 1/2 designation. Since then, I’ve put 50,000 miles on that engine. Thanks to timely oil and coolant changes over the years, it still runs smooth as silk.
Maybe they didn’t want to call them 3 ½ because of the pre-XK motors (1.5, 2.5, 3.5) but essentially they are 3.5 just as well… they could have cast 3.4 though. Marketing-?
Indeed, die-hard Jag people even in Germany sometimes still refer to the early XK full-size engines as “three-and-half litre”, even though this was never written on any outside of a car … maybe it has become the sign of the initiated who ever cared to stick their heads deep enough into the engine bay to read the letters …
Just checked out - the displacement was indicated at 3442 ccm. General convention would certainly not indicate the use of “3.5 litre” designation.
Good night
Jochen
75 XJ6L 4.2 auto (UK spec)
Autmobiles are ride with that:
-a 1200 Datsun is 1197 cc
-2 liter Rovers are 1997 cc
-1600 Datsuns were 1588 cc.
Marketing. 
Fair enough. Taxation might? But… The 4.2 XK is a bit over, isn’t it.
MOST examples at least indicate the tax class rounded up to full tenths. Until recently; now what you buy is no longer what it says anyway. C63, A45, 330i or what not.
And what, exactly, is a “Veloster?”
???
Thanks for the update, as I am unfamiliar with the engine designations, but you say the 8L is the better engine, and I would like to know what changes and improvements were made for those years. I understand the Series 3 cars are out there, and there were lots of them made, and I assume they have fuel injection. Let me know, and I appreciate your input.
The 8L block (all S3?) is machined between the bores and they might crack a little less. The rods are stronger and better and the block has been strengthened as visible on the outside. The long head studs still corrode, but it is about ten years younger. I am not sure but I think the oil pump has been improved. And it is cheaper. If you do want to fit it to your E type there are many things to consider, but it will be easier and cheaper to use the 8L block instead of one from an earlier XJ. The oil filter can be kept but for the cooler, but the fuel injection does not make sense to bring over, new oil pan, oil pump pick up, water pump? Many more. The block, most internals and the head will work with the existing E type parts that need to be put back on. If I were to take any XJ sourced block, it would be the latest I can find.
David
Thanks, and I believe I will get the original engine, as it is in pieces and the block has a hole in it. Lots of parts may have to be exchanged to fit it into the E-type, such as the oil pan and some accessories, and brackets. I like the two SU’s on the 73 engine, and I know what people want these days for a triple carb setup. All is up in the air right now and we will have to acquire the E-type first, but I am still tempted to go ahead and get the 73 XJ6. She wants very little for the car.