Driving a V12 on a single bank (6 cyl)

[Rui]

Jaguar did some testing in the early 70's to try reducing the fuel consumption of the V12 running on carbs, recall the engine was supposed to have had fuel injection BRICO from the beginning.One of the trials involved running the V12 on a single bank. Today I went for a short ride after having removed one of the two links between the carburetor control and the central round accelerator command pod. The car run perfectly but of course no 'kick' when I pressed the accelerator hard. When running on the left bank the gearbox acts very sporty, keeping higher revs presumably as the vaccum control is sensed on the left bank. Running on the right bank alone works as a more fuel save mode with the gearbox in lower revs. Next step will be to cut fuel arrival to one of the banks and to completely open the buterflies on that bank to have less resistance and see what the fuel consumption will be at low speeds. It will be very easy to devise a system where I can switch on/off bank A,B or both. At low speeds you can hardly notice only 6 cylinders are pulling the car! Has anybody tried this before?

BTW I disabled vaccum delay, much cooler engine in city drive and better mpg : 19l/100 km mixed road and 16.7 l/100 km in highway 120-140 km/h ! (on 12 cyl)


Rui Meneses
Etype series 3 1973 Sable beige

[PeterCrespin]

Yes I have tried it on 5.3 carbed, 5.3 injection and 6.0L distributorless injection Jags. As you point out, to make any difference you would need to cut the fuelling to one bank. On the E-type the fuel supply is a loop across both banks and back to the fuel tank so it is not as easy as simply putting a tap or valve in that side. Plus arranging the wide-open throttle is not trivial if you are to ensure no accidental operation! I will be interested to see how you get on. By having the disconnected bank left at idle you are not wasting as much power pumping as if there were absolutely no combustion, but it would indeed be more econimical with the throttles wide open and dry float bowls. However, it would then take time to bring that bank back into operation while the float bowls fill.

So apart from being an interesting project to watch someone else do, I don't see much real-world merit in it.

Good luck

[Heuer]

Have you thought about buying an S1? Six cylinders - job done!

[MarkE]

Have you thought about buying an S1? Six cylinders - job done!

I was thinking along the same lines....or a good old Irish saying....'If I was you, I wouldn't be starting from here' !!

Leave the good old V12 alone!!

[Rui]

There is a fuel loop indeed but it has a T to feed the carbs, so enough to replace the bottom part of the T with a loop fit with a XJ6 LH fuel return valve so fuel can be controlled with a switch. This is actually the only modification needed on the fuel delivery part.

As for the opening of the throttle enough to have a sphere/stop
where to hook the carb linkage rod, once it is unhooked from the pod so to keep throotles on the unoperating bank fully open. A job that can then be made in seconds.

Everything can then be Put back to original in 15 min. As I live in a city, not much sense to queue on 12 cyl before I manage to get out town, let's see.

Moreover I do not really see any disadvantage, possible damages, etc, the engine will run even cooler in the city.

The next step maybe a EFI conversion in a couple of years!

And yes, I did thought about buying a 6 cyl but mine was in great shape so I could not let the opportunity go! In addition is extremely comfortable with an excellent driving position.

Rui

[Rui]

But by the way Peter, did you note significant mileage increase?

[AussieEtype]

XK Engineering sold a kit in the early 80s for fuel injected V12s. Did not shut down one bank but various cylinders in each bank so became a V6. It also dribbled fuel into the shut down cylinders to keep them warm so when you put the foot down and brought all 12 back on line the unused cylinders were already warmed up and ready to go. Apparently worked well.

The modern Chrysler 300C V8 also uses a similar system.

Garry

[PeterCrespin]

No I did not notice a significant mileage increase. I think it was about the same for much less performance, but as mentioned I was just leaving one bank on idle and the difference between idle consumption or fuel used at an average 2000-2500 rpm pottering around is presumably not that huge.

If you want to do it out of curiosity then great, have a go. If you think it is going to deliver anything significant except having to stop every so often to clip the throttle rod back on, forget it. I think I used to swing the rod through 90 degrees after disconnecting at the capstan and leave it lying along the cam cover somewhere, but my memory is vague and the last car i did it on was the 6.0L which had a fancy cover over the valley.

Pete

[Rui]

@Gary : thanks, also Roger Bywayer told me something similar, and there is an article on the AJS engineering site. Indeed with fuel injection everything becomes easy controllable.

@Pete: will make a test in a few weeks/month when will have some time and will report back.
Thanks !

BTW on a more important issue, I should open another thread: gearbox leakage: Borg Warner 12j does not leak when driving but when stopped for over a day or so leaves half a glass of oil on the floor ! Level is ok and apparently is a common problem but can't even get decent pictures of the gearbox to see where the seals are etc... My Xj6 does the same but a less

Rui