Photography courtesy of Xcessive Manufacturing
Story by Rich Kobliha
The reincarnation of this XJ chassis was done completely in-house at my shop, Xcessive Manufacturing, from the suspension design and setup, to the engine assembly, fabrication work, and tuning. When the project was just getting started we asked around at a few local Jag shops and on the forums and found that either no one knew anything helpful about the original engines, or they weren’t sharing. The common theme was “Take it out and do a Chevy swap,” or “Just buy good parts and pay us to do it.”
After a bit of our own research, we came to a few conclusions. Basically, people are afraid of what’s not commonly done, and a lot of them just don’t know what can be done to begin with. These cars are a bit of an underdog these days due to the complete lack of anything aimed at mechanically upgrading the powertrain, and the typical Jag shops don’t tend to delve into boost, much less drifting.
The original engine design can be traced back to the 1950s, and remained largely the same—other than displacement increases—all the way up to the mid and late 80s. Even the bearings and cams would interchange, for 30 years! I’ve had a ‘74 XJ12L for 17 years as a daily driver, originally with a Rover V8 swap and Chevy auto trans, and now running a turbo Toyota straight-six (a 1JZ-GTE). When I first had that car I was sliding it around on stock wheels and suspension on my way to and from work, but gave that up when I realized I was scuffing the tires all the way up to the rim, basically about to roll the tires off the bead! It was fun, but a bad idea on a car that weighs over two tons.
Back to the XJ at hand though. While many are calling these cars old junk these days, we thought otherwise, but couldn’t argue with the prices that reflect so many attitudes towards these old Jags: this car was purchased for $600. In terms of getting to work on the transformation, we had to start weighing out our options. It has a considerably longer wheelbase and rather bloated dimensions for something to be used for drifting—it is about two full feet longer than a Silvia S13!—and the power from the factory was a little anemic.
The original motor had 158,000 on it, and we decided to see what it could do to freshen it up and get the power we were after. At 4.2 liters, it had size on its side, but it was built like a WWII airplane engine. It looks awesome of course, but we had to find out if the motor could get to where we needed it without spending too much money getting there. The first dyno pull was right after we bought it, with no work done yet. As it was, it made about 180 horsepower to the wheels, and similar lackluster torque figures with some blow by to boot. The factory tach says to shut down by 5,500 RPM, but we never got there, the power just dropped before that anyway. It had some small issues, so just no point in really pushing it. We found a leaky injector that wasn’t seated, a loose coupling to the MAF, and extremely dry wires, so we did only what we needed to. The oil pressure was in question too, but it had stock Smiths gauges and yes, factory wiring.
Getting to work on it after the initial tests and review, we removed the smog pump, mechanical fan, fixed the injectors and MAF, and hollowed out the catalytic converter. Then we did our manual transmission swap using a Nissan Z32 unit, and we used our clutch pedal kit that fits into the factory pedal box. We made some urethane motor mounts and threw on one of our Nissan urethane trans mounts to keep the 5 speed swap in place. We got wheel horsepower up to about 196 after that, and tried to rev it out a bit higher this time, though there is just not lot of power up top. After this preliminary work, we decided the motor was sufficient, and we chose to take it further instead of resorting to the easy swap of an American V8 of some variation. It’s nice that after all that’s been done to this car and that its new life, it’s still moving under the power of its original motor.
Continuing the build, the next step was a strip-down of the externals on the motor and a full teardown of the chassis. We managed to remove about 700 lbs from the car, including a bunch of really bad wiring. It’s important to note that we never cracked the motor open except to remove the valve covers and fix oil leaks on the rear. It really is a robust unit.
That’s not to say it wasn’t heavily modified though. We wired in a standalone management system to handle the added complexities of turbocharging the motor, fabricated a turbo header and exhaust, modified the stock intake to accept 550cc injectors, we made a top feed fuel rail along with a new fuel delivery/pump setup, and also moved the throttle body on the stock intake while upsizing the inlets. With this setup, we started with 7 lbs of boost, and on the dyno the motor did well except for a bit more blow by (no surprises there though).
Progressing forward, I kept tuning and upping the boost. The first turbo we used was a diesel generator piece acquired for just $125, simply to see what it would do. With a pretty interchangeable design, I knew I could swap it out easily for another unit if it didn’t perform well, but it was cheap enough to throw away if we lost a motor and hurt the turbo! We ran it all the way up to 15 lbs of boost in this configuration, and managed 360 to the wheels, and 460 lb-ft of torque.
With some issues plaguing the set up, we suspected the stock cams being a bit short on duration; but we still felt this would be plenty of power to see if the motor would stay alive when the car was put sideways. At this point, I had only seen pictures of the inside of one of these motors, and found some specs in a service manual, but I liked what I saw. The potential was there, but age was the concern.
Being a Jag from 1985 that was originally designed in 1968, the stock suspension was never meant to do what we planned, so we went through that aspect of the car next. We designed a rear cantilever set up that mounts in the trunk and connects to the factory lower control arms. This gave us all the adjustability of modern suspension that has never before been available to Jags of this era, with adjustable ride height, dampening, preload, and spring ratio leverage capable of being adjusted from inside the trunk.
The factory suspension up front was a separate spring and shock with a double A-arm suspension. We deigned a system to fit inverted coils between the arms that gave us the same modern adjustments that are required for a good track setup, while keeping it all attached to the stock suspension frame assembly, albeit with a bit of welding. While we could really set the car down low, we left the ride a bit higher to allow the 18” wheels to fit better inside the rolled fenders with the increased lock angle.
With the first motor pressurized and tuned and the suspension set up, we started driving it daily to and from work. After about a month, with a few (maybe more then a few) hits on boost, the oil pressure proved to be a problem, and we lost the main bearings and subsequently damaged the crank. A complete tear down of the motor showed me a few weak spots in the oiling system, due in part to its age of course, but also the design. Can you believe that Jaguar didn’t actually design a motor in more or less the 1950s that could handle 15 lbs of boost and more than double the factory torque output!?
It was hard to gather information, so we just learned what people couldn’t or wouldn’t tell us. We sourced a new (well, still from a 1985 car) donor motor from the junkyard so we didn’t have to start a rebuild with fried parts. We had it line bored, got bearing clearance on rods and mains all correct, balanced it, honed the cylinder bores, and set up the pistons’ and rings’ tolerances and clearances for prolonged boost.
It was a lot of work, and still more was to come. We polished the rod beams and balanced the pistons and rods in-house, all standard fare. We did the reassembly of the engine and all of the head work ourselves too. We put in all stock parts where we could, including the entire rotating assembly, pistons, bearings, rings (yes, 1985 piston rings!) and cams. I reworked a stock oil pump for better flow and tighter tolerances. You can buy “high flow” oil pumps, but that meant a pile of cash compared to a stock pump, so it was taken care of in-house for a lot less money. This was kind of a budget build, to see what can be done without throwing $5K or more at an LS1 motor or a complete pro motor build. We wanted to see if the 1950s-era Jag straight-six could make it happen in our world. All told, the junkyard motor, machine work, and parts totaled just $1400. Of course having a shop helps with that!
With the new motor all together and installed, we hung a new Comp turbo in place of the diesel unit, and started breaking it all in soon after. Unfortunately due to other obligations, we weren’t able to put the car back up on our dyno yet, but data logs in the passing days showed faster spool-up and more fuel being used, so it should be making more than it had on the previous setup.
The new turbo was a nice improvement; it was pulling hard. Oil pressure stayed rock solid, and the motor was smooth. Four days after the first crack of the throttle on the new motor, we took it to a two day drifting event. With our new suspension and a new motor, both virtually untested for what it was about to do, we wondered if it would work sideways for prolonged periods. The motor proved itself a contender though, and the suspension worked flawlessly all weekend. Power came on strong around 3,000 RPM, and pulled hard to the rev limit we had set at 5,800. It pulled the 3.55 gears flawlessly, and the torque was amazing from the 4.2 liter motor. Justin Lucas did a great job driving the entire weekend, and I managed to keep it on the track a bit myself throughout the event! A stack of tires later, we had successfully built the first old school drift Jaguar XJ6, with the stock I6 and without a complete “modern” suspension swap! Believe it or not—thanks in part to our custom molded and upholstered bucket seats—it’s still a nice drive down the road too, as any good Jaguar should be.
