I've found that about 40mph there is enough airflow to not need a fan fwiw, the temps start coming down to highway-norm and the fans drop out. That's with the stock condenser and a stacked plate style radiator and oil cooler under it covering part of the radiator.
And PWM fans are the bees knees, they can aim for a target temp and avoid both the cycling up and down of temps and the sudden hit on the electrical system from high speed fans engaging.
Even among v8's the LT1 has odd cooling behavior but between the decent aluminum radiator and good fans and shroud the improvement was impressive vs a large copper/brass unit and a pair of strong single speed fans.
184f @70mph, 193-197 in town with the AC on and you never hear the fans, at 90f ambient. It cooled well enough before but the rad had been leaking, again, for ages so figured I'd experiment a bit.
I would imagine the v12 is more difficult to cool but this setup seems to have plenty of capacity. I'm eager for a 105 degree day to see how it acts.

 

A couple of observations:

-If you do a swap of anything, you will need to understand and observe the rules of driveline angles. Otherwise you will have vibrations and broken U joints and other possible side effects like cracked tail shaft housings ( don't ask how I know). Also note that the Society of Automotive Engineers publishes a manual of driveshaft design, you'll need to know everything in it - and it's 440 pages.

-Holley EFI isn't all it's cracked up to be. I have a friend with that system on a Chrysler with a 440. It's ok, but not great. Part of the problem is that it is self learning and there are not manual adjustments and over rides. The self learn can be fooled by things like a lumpy cam and isn't that great for fine tuning. Don't expect starting and drivability to be equal to the XJS V12. If you are getting that sort of power from a 351 you're not going to be having a smooth idle and that EFI system probably wouldn't work well. It needs a smooth vacuum signal to work well.

-Transmission: if money is no object the choice is easy: ZF 8 speed and controller. A compact transmission that is very reliable, it's smaller than the TH400 and will fit in the tunnel. I believe there are versions good to 900 N-m of torque now, but double check that.

- As a general comment, these swaps will take a lot longer, cost more and become far more involved than you think they will. The XJS is a challenge especially because of limited space in the engine bay. Consider that the 351 doesn't fit in the engine bay of a Lincoln Town Car with EFi because the manifold is too tall (unless you manage to get the special Mustang manifold that was only used on the Cobras for 1995), and the XJS is a shorter engine bay. Take lots of measurements before you start to ensure the engine will actually fit.

 

I bought this '89 as a roller package with no v12 engine in 12/2000. In 4/2001 I was driving it and this month it's been on the road for 24 years. Still runs and drives perfect. I used a Griffin universal race aluminum radiator. It fit the stock Jag location like a glove and was rated to 600 hp. It keeps the lt1 at 180 degrees on the hottest days. I'd say it would work on any engine you had. I even used the stock Jag shroud with a single 16" fan from late 80's Camaro. I do remember a little hesitation at the price of $350 20+ years ago.

 

That is excellent, how many miles on it? I rolled over 250K on the car and about that on the motor on a trip to the east coast last Christmas since ours got eight'd about 15 years ago at 100K.

 

Thanks, it had 59k miles when I got it and 122k miles as of today. You got a lot of seat time on yours.

 

I definitely understand the concern of it being an ambitious under taking and being costly. There's no plan to have this car done by Friday. This whole project was meant to be a large automotive lesson that helped supplement my college experience. I'm very thankful for all the insight.

As it stands, it seems like my option might be to try the 4r70w behind the Windsor. I'll account for drive shaft angles during the mounting and fabrication. Based on Greg in France (wish you were Greg in Minnesota) I'll rework the vehicles heating package. I'm also gonna take your advice on that custom bumper cutout I think.

It'd be a dream to get the engine to fit without holes in the hood or something custom but we'll see once things get measured and custom mounts are made.

I've already bought Holley sniper 2 EFI and so I'm going to have to make that work. And I'm most likely going to have to do a lot of learning about making the entire circuitry work for the vehicle.

Is there more that I'm missing? I've heard different things for transmission control systems. Some have said the Holley system can make it work while others name different brands. Ideally I want to keep this portion as simple as possible and I love the XJS shifter so id like to have something that allows me to keep that also .




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Far as I know none of the TBI Holley systems to trans control, some of the port injection ones do I believe.
You'll need this with the S2 https://www.holley.com/products/fuel...parts/VK103470
I'm pretty sure there are other options, maybe a bit cheaper but this one will control through the screen for the S2 which is kinda handy.

Need an ignition system too, I think Holley has some offerings that integrate as well with the S2. Stuff get's expensive quick....

You'll find a million little things, AC lines, PS lines, routing things, all sorts of stuff.

 

Looks spotless, there's a reason I don't show mine off lol. I just the other week finally replaced the stock hood pad that's been dropping
oily goo and dust on everything for the last fifteen years. Very function over form this ole thing of mine at this point. She sure does function though.
Iron head LT1 from an impala, tuff as nails and does not make enough power to hurt anything I did the LS coil conversion four or five years
ago and that was about the only trouble the engine ever gave. Put a valve body in the trans couple years back, it was rebuilt when the engine
went in. Been a good setup. The rest of the car keeps me entertained with things going weird from time to time.
I don't drive near as much as I used to, worked from home for years now but have put a lot on this one for sure. Easy to rack up miles
in the midwest where things are long and straight, good place to be in an XJS most times.