Build Log SCF/RCR Jaguar XJ13

It has finally arrived and now the work starts. This car has been a dream for more than 10 years when I first saw a replica on ebay and the seed was planted. I have been a long time Jaguar fan since my dad bought a 61 Mark IX when I was 11 years old (1969). I also just bought a 1960 Mk IX this spring and it is currently getting a through redue. Now I have two concurrent projects although this XJ13 is certianly going to take much longer. The car is planned to be a road car with maybe a few fun days at the track/year. As you can see the engine is in the car. Gear box is a G50. The engine was built by Chadbourn Bolles and started as a 6 liter Jaguar V12. It has been bored and stroked to 6.8 liters (416 cid). It has had extensive head work, Isky cams and CR is 13:1. The plan is to use 6 twin (twelve individual) TWM throttle bodies (which I have). Fuel and ignition will be managed by Electromotive TEC3r ECU. Cooling will use an electric water pump. More details will follow in the next few weeks.



Missing a few cylinders
Mike, I'd be very interested in knowing more about your electric water pump.

Keeping 6.8l of high performance Jag motor cool will be a real challenge. Shoot, the factory never figured out how to keep the 3.8 or 4.2 sixes cool!

(Well, maybe the cooling system was "fit for purpose" for English summers, but not much more :))
I am planning to use a Meziere pump through a guted pump on the car. The reasoning is the distance to the radiator and to help prevent heat sink issues during cooldown. I do not see cooling as a big issue yet.
Red Baron
I have previously seen your car in photos very nice!. I was originally planning a similar intake and perhaps I will live to regret my change to the 12 throttle bodies.
Thanks for your help in getting the dream on the starting line. No doubt I will be bugging you just a bit as it moves along:stunned:
What are you putting the BMW V12 into?
These large V12 engines do produce a substantial amount of heat. The achillies on the Jag V12 is when owners running them chronically overheated leading to a droped valve seat. This usually occurs in a poorly maintained XJ-S that had an issue with unseen debris clogging the lower 1/3 of the radiator. If the engine and especially the cooling system is maintained these engines will easily go 300k miles even when dragging around a 4000+ lb car. I have a final version XJ12 (1996) and they finally solved any cooling issues on that car. It has a large mechanical fan and two electric pusher fans. The later run in traffic and will run for some time post shut down to help prevent heat sink problems. That car never runs hot. I think with the electric pump and twin fans I should be able to control engine temps farily well.


Missing a few cylinders
Still undecided (as Fran well knows), but the XJ13 is high on the list :)

I really hope the electric pump works well for you as I was planning on using the same pump, or possibly the Stewart.
Thanks Mike, I have a BMW V12 and was planning to do something similar.

John a BMW V12 in an XJ13? I have no doubt it would work nicely plus you have it. However, I wonder about the choice for an XJ13 simply because Jaguar V12's are great motors and can be had very cheaply unless you want to modify them much. Of course modifying the BMW motor would probably cost even more. I originally bought a 6 liter motor to put in the car but then found a good deal on the current motor so I still have one in the garage.
If you are going to all the expence and time to build an XJ13 it seems logical to me to put a Jag motor in it as it is set up to take that engine. On the other hand I suppose I could be convinced otherwise since it is not possible to get one of the original motors.
Fran, Red Baron is my nom' de plume'. Old engineers like old soldiers, never die! Regards, Paul Straub
Your car looks gorgeous Paul.
Thinking (a long way) ahead, could you tell me where you found your front orange indicators/repeaters? Would you say they are close to the original dimensions?
I had a brief discussion with my engine builder Chad Bolles and he planted an idea in my head that has become tough to exorcise. He said if he had this car he would put a Lamborghini V12 in there. Seems over the top at first thought but then the idea starts to creep in to my brain causing all kinds of havoc.
The 2 valve Lambo V12 had the intakes between the cams just like the original XJ12. I have seen a number of people talk about building a twin cam Jaguar V12 using Jaguar AJ6 heads. It is a quite engineering feet but some have actually done it successfully and I have even see photos of XJ13 repilcas with this set up. The problem is that although in theory one is trying to replicate the orignal cars DOHC set up it looks nothing like the original because of the intakes are not between the cams. I would even argue that although this is an amazing setup it looks a little clumsy and much to modern for an XJ13 replica. Even to the point that the SOHC Jag V12 looks more period correct. Another big issue with building one of those monsters is that it would add significant weight to an already very heavy engine with all the additional weight on top dramatically raising the center of gravity. Jaguar actually tried this for racing in the 80's and abandoned it due to the center of gravity issue.
Ah now the Lambo motor could be made to look correct. Tha valve covers could be remachined to look like the Jag type. The lambo motor is substantially ligher. The largest 2 valve Lambo V12 was 4 liters and about 400 HP which would suit the now 2200lb car nicely, however, it can be stretched to 5 liters and 500 HP which was the goal for the original XJ13. It does not have the large central dizzy in the valley but I think could live without that.
Now I only have one minor issue and that is to pick up one of these motors. There must be tons of them just laying aroung and cheap too:thumbsup:
I think I will continue my build as planned but I expect to be haunted by the Lamborghini V12. I will also probably be lurking in all the usual places looking for that bargain Lambo motor for quite some time for a future installment.


Silver Supporter
An American built reproduction of a British classic with an Italian engine and a German transmission. That will take a bit of time to digest.

Interesting concept, nonetheless.
Yes it is a bit of an unusual concept but the point would be to try to create a more accurate look. Performance and sound would also be excellent. The lambo motor as I understand can rev like anything. Not sure of the redline offhand but it has 5 figures.
The down side of this engine with the proper machined intakes and other necessary stuff to make it run correctly would likely be a cost north of $50k not including the transaxel etc. This way is out of my range for this car.

Alan Watkins

Lifetime Premier Supporter
Performance and sound would also be excellent. The lambo motor as I understand can rev like anything. Not sure of the redline offhand but it has 5 figures..
In it's most highly tuned form (Miura SV) the 4 liter engine was claimed to make 380 at 7,800. Many people scoff at those as being "italian" horsepower, however, including, I believe, Bob Wallace himself. Safe redline was no more than 8,000, I believe, and that was accomplished with very stiff valve springs. So I don't think you're going to get XJ-13-type horsepower that way, although I will defer to Chad on that. He definitely knows his Lamborghinis.