The goal:
To put this 351 Windsor engine in my 1987 XJS.
*With Holley EFI
​​​​

What I currently know:
-Transmission needs adaptor bell housing(in progress)
-Custom motor mounts need made (in progress)

What I need help with:
Theoretically what all needs to go into just making a foreign engine like this working with the car ELECTRONICALLY.

​​​​​​What parts of wiring harness should or need to be saved?
Can most of the old stuff go?
How would a new system affect things like relays, fuses, resistance etc.

Any ideas and discussion would be great. I'm not looking for any "it would require too much... So can't be done" or "why would you?" Type of stuff.
Thanks for help guys. This is a big project.

 

Having done a swap on another vehicle, you find you do not know what you don’t know. On the surface, a SBF with a Ford transmission should work; your Jaguar shares u-joint sizes, so a good driveshaft shop can shorten or retube what you have to work. No guarantee that it will fit the tunnel, and you will need to fab a trans mount. Engine mounts will have to get driveline angles correct, and clear the hood , aprons, and unibody rails. Radiator shouldn’t be too hard, but figure an electric fan w/supporting wiring, sensors, and relays.
Electronics get iffy; the Holly Sniper EFI is pretty much a stand alone requiring power and ground, where it get complicated is if the trans requires electronic control. And you still need temp gauge, oil gauge, and fuel pump provisions.
Exhaust will be 100% custom, you will have to figure out the power steering, alternator, and a/c compressor mounting and connections. A fun project if you have the skills, but a lot of stuff to figure out.
Don’t cut or throw away anything!

 

As it stands the engine is built with accessories and just needs to go in.
I was planning on keeping the th400 so that everything just "bolts right back up" essentially. I didn't want to deal with transmissions and driveshafts more than needed.
But you think the old wiring harnesses will still be needed with the v12 gone?
I'm not super worried about gauges functioning right now necessarily.
Thanks for your input. Really good stuff

 

Don't eliminate any wiring until you're sure it won't be used

Ignition "+" wires, gage wiring, a/c compressor wiring, fuel pump wiring can be used with the new installation

Cheers
DD

 

Personally, if I were to swap motors, I would go with a Ford trans. AOD have a pretty good reputation- why stick with a 3 speed, no lock up converter, that requires an adapter?

 

I agree with not removing the wires yet but most will be removed. Theres not much information on this swap other than there were clearance issues because of the front sump oil pan not clearing the rack. Have you test fitted the engine to make sure it fits? If you could give a description of the engine, year, fuel injected etc would be helpful.

 

Unless this is a performance oriented deal, I very, very strongly suggest using an OD transmission. Pretty sure ford has several that will bolt to the 351, controllers are out there, making a mount and having a driveshaft shop fix that part up isn't a big deal.
I suspect you're going to find with the stock really tall gearing in a deceptively heavy car it's a dog even if it makes good upper RPM power, and if you re-gear it your highway rpm is going to suck. The OD trans helps a lot with both of those. TH400 is a fine trans and if you're drag racing or something probably
cheaper to work with than an OD box, but if it's a driver, nahhhhh. Bite the bullet unless you have a really good functional reason not to imo.

Other than that, with a standalone engine controller you don't need anything from the car basically. You'll want stuff but most of it's obvious, gauges, get the ignition switch to work, etc. Fuel pump may have a pressure the Holley will work with even though the stock system
is a trainwreck.
You need the wiring diagrams for the car unless you're going to just rip it mostly out and start over. If you can't decipher factory wiring diagrams, you can't integrate the swap effectively. Nothing personal, just a required skill set.
A loooot of the jag wiring can go eventually but figuring it out as you go is best, and sometimes the way things are routed it's better to just tuck away and leave the
original stuff alone. You see a lot of these swaps, usually for sale after sitting for a decade for $1500 bucks, with no AC or power steering and butchered wiring that never really worked because the swapper wasn't committed to what it took to make a real functioning car out of it.
It's not a trivial deal but plenty do-able. I've got 15 years and 250K miles on a perfectly functioning LT1/4L60E XJS that I'd quite literally drive anywhere and the only thing that has never worked is the rear defroster lol... This is probobly one of the most driven XJS's in the country at this point.

If it's a drag car or such, cut all that factory crap out and buy what you need from painless wiring to make it happen, switch panel, fuse block, etc. I'd still replace the trans, it's going to break if you beat on it.
You'll need gears and maybe NOS or forced induction to move the heavy thing at other than weekend fun speeds.

 

Really good input from everyone thanks.

How did they make the v12 work with a th400 as a gt car if it's got bad gearing and no OD?

Also yes the goal is to make it a nice road going cruiser. What's the best transmission? And will it fit. The engine makes 540 lb ft and 475 HP. If that helps anyone

 

You are going to sacrifice all of that engine’s potential if you don’t go with at least 4 gears (either auto or manual) and change the gearing. The original configuration of the XJ-S is for a comfortable tourer capable of cruising at 100+ mph, using an engine of 300hp. Adding that much power and torque requires deviation from the OE setup to maximize performance. Plus you will break stuff, guaranteed.

 

Well, you have to understand the history of things with Jaguar....a company a bit infamous for sticking with older technology.

Jaguar started using the TH400 in 1978. Although the design was 14 years old at the time it was still a viable choice. It was smooth shifting and as good or better than any other 3-speed automatic out there. And 4-speed automatics with OD were not really a thing yet.

For a window of time in the late-70s/early-80s the XJS performance was as good or better than the competition, even with the 400 transmission.

But, as time marched on Jaguar didn't keep up. The XJS was still using the 400 transmission (and 5.3 engine) clear up until 1993-94 when the 6.0/4L80E combination was installed.

In this day and age it would be a bit of a shame to do an engine swap while keeping the old 400.

Cheers
DD

 

Also, I am assuming you have the dynamometer sheet for your 351; look at torque at 1300-1400 rpm- that is what you are dealing with if you keep the stock 400 trans. I wouldn’t be surprised if the Jaguar 5.3 had similar torque at that rpm, which is the torque converter stall speed- if you don’t go with a higher stall converter, stiffer final drive, and lower first gear you won’t launch much better.

 

Yeah it was a different era, and Jag was sometimes not just on the forefront since they seemed to be perpetually broke as a company.
They really didn't have a choice, they had one "big" engine and OD trans weren't a thing so they got one that would more or less hold up and
geared it to be a highway+ car. A heavy car with tall gearing needs low end torque, the v12 wasn't really big on that and I wouldn't imagine a 475 hp small block will be either.
One of the reasons so many people used the old GM TPI and LT1 motors is they came with an overdrive that's that had a low first, a good converter locked up overdrive, and made most
of their power at low rpm's out of the box. Imagine you're picking a motor trans and gearing for an Impala or an older crown vic or such and you'll be on the right track for a driver.
There's an element of personal preference though of course. Generally speaking I like auto trans cars to have boat loads of lowish end torque and manual trans ones to make power
with RPM, because it's fun

I've had pretty good luck with the 4r70w fords, much like the later GM ones they were significantly more pleasant/durable and "smarter" than the earlier generation OD auto trans they were based on, the AOD in fords case.
Not that you can't build an AOD to work. The AOD, not AODE, was also a mechanical trans with vacuum and a throttle rod to control shifts so that'd get you out of needing a trans controller.
I'd go with an electronically controlled one for the tuning ability though.

 

You guys could charge money for a seminar and it'd be worth it's price. My last thing is this:
If you had this scenario with a SBF in an XJS with the goal of making it as "GT" as possible. What's your transmission of choice. Ideally if money were no object. The goal being that the car is responsive and ultimately reliable and good to drive. Thanks
​​​​

 

A manual


4R70 or 75W otherwise for a ford. Holley probably has an engine management setup that will control it, there are standalone ones otherwise.
If you don't have most of your torque in by 2500-3K RPM it's going to be pretty blah feeling I suspect. The iron head LT1 is all in
at about 3K and it's a little soft around town imo. Your typical small block performance build tends toward making power at higher
RPM's and you just can't use it unless you have a manual or steep enough gears or stick your foot well into it all the time.
Heavy cars with tall gears got big ole torquey big blocks back in the pre-smog era when nobody cared about MPG for good reason.
The XJS in general really shines at interstate speeds in the US, it's okay around town but a little cumbersome feeling, not having a bunch
of low end torque on tap make it worse. 70 and up is it's happy place. It's still a fine daily driver, least out here in the midwest where
there are lots of long open roads and generally pretty high speed limits.
I drove it back to NC over Christmas and with 55mph speed limits and less long calm roads and it was
surprising how less well suited it was. I think if I lived there I'd put steeper gears in it even with the OD trans.
I kept it in 3rd a lot out there.

 

Interesting observations. I drive my 90 XJS convert around town a lot. You're correct that it really loves 70+ speeds. 90 feels like 60 except for the growl of the exhaust. In town, it's fine although gas mileage, never good, suffers. Also in the NC summers, while mine never overheats, in town you can feel the heat rising around you, especially at stoplights. I also have to chase down the gas tank venting because it builds a lot of pressure, only relieved by opening the filler cover.

 

Heat is a real issue in these, even without cats if I leave anything on the rear floorboard for any length of a drive in the summer it's quite warm after.
The tank venting thing is a pretty common issue, think it's covered in Kirby's Book pretty well. Enough pressure can stress the tank and cause leaks
so don't let it do that for too long.

 

As part of the heat issue, what are the things they did wrong and could have done better (besides having a massive v12) so these cars weren't such heat magnets. And is this still an issue if theres a different engine in the car . Like the i6 even.

 

Mine is a catless LT1 car and the floorboard is still bloody hot in the summer. The trans tunnel and floorboard and I've even felt the rear seat bottoms warm, and the sides of the trunk where the exhaust are is not
the place to put your frozen items after a grocery store trip lol..
I think it's just the packed-in-ness of everything, maybe the airflow underneath.
If I had one stripped down I'd apply a lot of heat barrier insulation, it's tolerable if the AC is working well, just a quirk of the car.
One of many. I've wondered if the relatively short life of the steering racks are due to the heat, Jag tried to shield it a little
here and there it looks like.

 

This is a very interesting and somewhat controversial topic! My car, a non-cat V12 UK spec has never overheated, summer or winter, regardless of air temperature. Ir certainly has experienced 100°F temps no problem.

Point by point, and in my view the MOST important, is:

• airflow through the radiator stack. When I rebuilt my car in 2009 to 11, I replaced the old OEM "hedgehog" single tube oil cooler with a later normal-finned rad type. Once using the car, I noticed that after a hot stop, eg in traffic, it took far longer for the coolant temp to reduce to normal once I got going. This was because the new-style cooler was far taller than the old hedgehog one, and there were no gaps in the front stack (oil coooler and aircon condenser) for clean air to get through. As an experiment I unbolted the front bumper and tried it, well the difference was night and day! This because the radiator needs a supply of clean unturbulent air to function well, and the front bumper, the horns, and the secondary coil (in my case) prevented that. I fixed this by relocating the horns and the coil to the sides, and cut a slot in the front bumper. Problem solved; but
• Other things can contribute mightily to helping too: First fit an electric main fan and upgrade the OEM secondary electric fan. I have a 17 inch SPAL pulling 25 amps instead of the belt driven main fan, mounted as close to the radiator as I dare (3/4 inch). Together with a 12 inch SPAL in place of the OEM electric - which is wired to always be on when the aircon compressor is activated. The electric fan means even in traffic the airflow through the radiator stack is enough to cool the engine. You do need a 115 amp alternator and a bigger than standard battery though. Also forget feet/second claims from fan makers, just a buy a SPAL or something equally reliable with the highest amp rating for the maximum fan size you can get in.
• Next, ignition system plugs and HT leads must be top condition, a misfiring or off tune engine will run hot.
• Not strictly needed, but an aluminium radiator takes a lot of weight from well ahead of the front wheels, may improve cooling, but will help turn-in!
• Renew thermostats 82°F ones every 5 years, they work hard. If you have an ABS car the follwong mod is not possible, but if a mid 1980s Lucas car you can get in a proper header tank where the washer bottle is, and move the washer bottle. see attached pdf.
• I am not convinced that providing an electric fan is close enough to the radiator, a fan shroud is needed; you can fit far bigger fans without one, but then you have to provide fan fixings A good easy solution is to buy something like this and drop it straight in and ditch the OEM: https://www.ebay.co.uk/itm/166285282...Bk9SR5rZkdTGZQ Also the foam packing round the radiator sides and on top of the gearbox should, in my view, be removed. Getting air into and through the engine bay is very important, and these things prevent it entering and exiting. The OEM bonnet liner is also too thick and prevents airflow over the top of the engine, remove it and replace it with modern 1/4 inch or less thick adhesive stuff such as this:
  Amazon
  Amazon
  the thinner the better.

You can also remove the OEM radiator top panel and replace it with a flat strut to locate the radiator and the aircon condenser, which again gives a far bigger gap on top of the radiator for colder air to get into the top of the engine bay:

This is my car now, one strut locates the radiator and aircon condensor/oil cooler stack, and there is another locating the fans from above. At their base, they are fixed to the chassis cross member to which I have welded studs onto which brackets from the bottom fixing eyes on the fans are connected.

 

This is a thread where engine bay temps are measured and discussed quite informatively:
https://www.jaguarforums.com/forum/x...atures-166641/