Hi all,

Thought I would see here who may have some historical information.

Below is a video interview at Goodwood, speaking with the Jaguar representative/driver Richard Mason who drives the XJ13 around the track.

Richard clearly stated in this 2016 interview that the original 4.8L quad cam V12 had a special firing order that gave the XJ13 it's unique sound.

I would love to find out what this firing order is and maybe try and replicate it one day on a 5.3 unit.

Does anyone have information on this?

Watch the video... @ 4:16 when Richard says this quite nonchalantly!




Cheers
Craig

 

Hi - first of all, the original quad-cam was 5.0 litres and not 4.8.
Also, Richard is wrong to say the firing order gave the "quad-cam" its distinctive sound (if thats what he said). It uses exactly the same firing order as all Jaguar V12s (1a-6b-5a-2b-3a-4b-6a-1b-2a-5b-4a-3b). This is pretty standard for all V12s.

The first of the XJ13 prototype engines to run (now in my ownership) was tested on the Jaguar testbed by the late Ron Beaty (who later formed Forward Engineering). He did run it in two different ways. The first way is exactly the same as the later V12 but he tried out a different firing order in period. I also tried it and found that it didn't run as nicely, sounded "lumpy" but did run.
There is a 15 degree difference between the banks. It is possible to first fire 1a on one bank then fire 1b after the crank has rotated by 15 degrees. Both these pistons operate on the same crank journal. Then you fire 5a followed (15 degrees later) by 5b. Next is 3a followed by 3b. Then 6a/6b, 2a/2b and 4a/4b.
In this way the firing order runs up and down each crank with each pair of pistons on each journal firing in rapid succession.