Hello everybody. Ill be acquiring a 1990 XJS with the 5.3 HE engine as a project car within a few weeks, it has just a little over 74K miles. I have a few questions that I would like to get answered. I have tried searching for the answers but for some reason I haven't find them.

1. Can you swap the 5.3 HE heads to the 6.0L heads?
2. How much can the lower end with stand? I know the engines can handle 8K rpms, can they handle more? How about with force induction?
3. Does anyone have experience with the TEC3r ecu and XDI ignition system from electromotive?
4. Does the rear end assembly have any weakness when it comes to putting power down to the road?
5. Has anyone tried swap the spindles for the wheels so that they are a more common bolt pattern?


Uh, that is all I can think of for right now.
I appreciate the help. Thank you

 

Welcome dude,

There are plenty of knowledgeable guys here, so I'm surprised nobody has jumped on this yet. I'll give you some general answers to your questions, and, hopefully someone with more experience will chime in with specifics.

1. Here is a great thread illustrating the differences between the 5.3 HE and 6.0 heads: https://www.jaguarforums.com/forum/x...0-heads-89458/

2. The bottom end is pretty bulletproof, and occasional excursions into the 8k range can be tolerated, but, unless you plan to balance your rotating assembly, You shouldn't hang out there very long, or often & you really don't want to go any further than that. Not that you will be going anywhere near that RPM range with the stock transmission.

The crank is forged, but, the pistons and rods aren't, and, your compression ratio, being 11:1, is a bit too high for forced induction. You''ll want to get a forged piston & rod combination that brings your CR down to at least 9.5:1 if you want to run anything more than about 3psi boost.

3. I have a TEC1 in one of mine, but, I don't have any experience with the TEC3r, nor the XDI. One member, named calvindoesntknow, was talking about using that setup in his project, but, I don't know if he's gotten that far yet. See this thread: https://www.jaguarforums.com/forum/x...-pre-he-95447/

4. Regardless of whether your differential is labeled Dana, Salisbury, or GKN, it's a Dana Power Lock. Yours being a 1990, is likely labeled GKN. The diff is strong, but, this rear assembly, as a whole (in stock form) was never meant for hard launches. The cage assembly is mounted to the rear subframe with 4 rubber insulated mounts, and the trailing arms have rubber bushings at both ends. Hard launches cause the rear end to squat, and the torque makes the bottom of the assembly tilt forward, inducing wheel hop. This can rip apart your rubber mounts and trailing arm bushings in short order if your motor puts out much more than stock HP and torque levels. There are various ways to correct for this, but, care must be taken not to lock things down so tightly that you limit the suspension travel, and consequently negate the passive rear steering in the process.

BTW, your final drive ratio is 2.88:1, which is great for top end speed, but, not very good for low-to-midrange acceleration. It also is completely mismatched with the shift ranges of your GM Turbo 400 transmission. Actually, it's your transmission which is not well-matched to either the motor's power band, or, the rear gearing.

5. The XJS has a standard Chevy bolt pattern found on Corvettes and Camaros, and, is also within a millimeter or two of BMW's bolt pattern, giving you plenty of wheel choices. However, the XJS doesn't use the mounting studs to center the wheel. Instead it utilizes a hubcentric centering design, in which the hub carries the load, rather than the wheel studs. I can't remember the exact diameter of the hub, but, it is larger than Chevy's, so you would need to have the centers machined to size in order to fit most Chevy wheels. It's really not that big of a deal, so long as the wheel you choose has plenty of meat around the hub area. Alternately, you can use wheel spacers to bypass the whole hubcentric thing, and chances are that you would need them anyways in order to achieve the correct offset for the Jag wheel wells.

There have been several threads on this topic in recent years, so it won't be hard to research the subject on this site.

I hope that helps somewhat answer your questions.

 

Thanks jagzilla. I guess I got a little confused, I thought there was pre-HE 6.0L heads but never mind. As for the bottom end is there a few threads on maximizing the strength to resist torquing the assembly forward without locking up the suspension? I am planning to do a manual conversion but I haven't decided if I want to go with a 5 speed or 6 speed.

 

I can't recall any threads about that on this forum, but, there are threads on the jag-lovers forum. A simple and effective way to do this would be to connect the tie plate, which is under the diff, to a fixed point under the car, and directly in front of the tie plate, using a length of threaded rod, metal tubing, or, better yet, a short suspension tube with Heim joints and jam nuts, so that it has some adjustability.

Coincidentally, I will be addressing this issue to some degree on JagZilla this coming weekend. I will be replacing the stock trailing arms with threaded aluminum suspension tubes with adjustable Heim joints on each end (see attached photo). This is not the absolute best way to take care of the problem, but, it will do until I build the new exhaust system. The smaller linkages in the photo will be used to attach my rear anti-sway bar.



The best solution I've seen to this problem, and what I will eventually do on my car, is what Robert Knot did on his track car, but, this probably can't be done on a car that has exhaust pipes exiting the back of the car, as the new trailing arm configuration would cross through the space currently occupied by the exhaust pipes. If you have Facebook, take a look at this photo album of Robert's, to see how he tackled the problem. In fact, everyone interested in improving the performance of their XJS should study all of his photo albums pertaining to his track car.