Written by Tom Sanders Monday, 02 November 2009 10:23

Jaguar XJS to 6.5L Diesel Engine Swap

My initial intention for the Jag was to put a Small-Block-Chevy (SBC) in it. Having had the opportunity to drive a number of different Jags, I must say that I have always enjoyed the Jaguar ride: it is an awesome vehicle to drive. My wife liked to call her ‘93 Jag Sex on Wheels. I don’t know that I would go quite that far in trying to communicate the thrill of driving one – but they are a great ride.

The electronics and power plants, however, have always left much to be desired. The V12 is notorious for dropped valves (which I think had been the case in our motor) and the Lucas wiring is way beyond quirky… leaving no doubt why a normal conversion path involves using a GM motor as the power plant. This SBC arrangement mates the awesome ride of a Jag with the reliability of a GM. That there is a lot of support available for such a project – it has been done often enough before – is a bonus.

Never one to go the normal route, I began looking at various engine options. One of my early considerations had been a GM diesel of some type. I initially shelved the idea due to weight, size and power issues. I have ultimately come back to the GM diesel for a number of reasons.

Here’s Why…

First, there is what I would call the cool factor. There really isn’t a cool diesel car to burn biodiesel in. Most of the television spots you see on biodiesel will show some guy collecting grease at a local Chinese buffet and pouring it in a beater Mercedes or Volkswagen covered in green Astroturf. Who wants that? Second, a supercharged diesel would help with power, lowering the top profile of the engine and also help with dimensional issues. Third – and here is the question I ask whenever I get inquiries on oddball and gas-to-diesel projects – is there a SBC kit available for the car? If there is, it makes the swap far easier. The SBC, 6.2 and 6.5 diesels all share the same form factor, so a kit with motor mounts, adapter plates etc. for the SBC would work for the earlier GM diesels as well.

Getting to Work

Once the bonnet is off and the motor is on the way out – you get a feel for just how big the OEM V12 really is. I am thinking we might even get away without having to do a spring kit or suspension work to the car. I might be wrong but I believe the stock motor and the GM diesel weight are about the same – we’ll see. The GM should weigh in at about 900 pounds fully dressed. The Jaguar transmission was originally made by GM – the plan is to upgrade to a GM four-speed. Installing the GM transmission will also require a few modifications, but we’ll cover that later.

Pulling Out the Jaguar V12

Diesel Engine Swap

Once the bonnet is off and the Jag V12 motor is on its way out...

How we built this engine…

Now for the fun part. I know I will get some flak for this but the block I chose to start with is the GM 6.2 liter 660 casting. This is statistically the strongest of the GM diesel blocks. I know the new Navistar and XL 6500 castings are all the rage right now, but there is so little data on the fleet that it is impossible to say how they will really hold up. On the other hand, having disassembled thousands of these engines, I can say the 660 block shows web cracks in about one per 200 examples. The particular block we chose was first