Usually for Glorious Garbage, I’m highlighting some embarrassing and yet fascinating car, something that encompasses both the glory and the garbage of the automotive world. This is one of the most majestic classifications anything in the automotive world can hope for, and deciding what makes it in or not is a job I take very seriously. Somberly, even. This time, though, it’s not a whole car we’ll be talking about, just the heart of one. The engine. Specifically the Jaguar AJ126 V6 engine.
This engine has had some pretty flashy homes, from the Jaguar F-Type to the Jaguars XJ, XE, XF, and F-Pace and the Land Rover Discovery and some Range Rovers, like the Range Rover Sport HSE. These engines were almost always offered in cars that also could be had with the bigger 5-liter V8, and there’s a reason for that, and that reason is what makes the AJ126 V6 such an amazing Glorious Garbage candidate: it used the same block as the V8.
I don’t mean a cut-down block like so many other V6 engines that were derived from V8s, like the Chevy 90° V6 engine, derived from the Chevy V8 small block, but with the numbers three and six cylinders removed. As in removed removed, with the block physically reduced in size.
Jaguar, though, didn’t bother to actually remove the unneeded cylinders, and instead just got rid of the pistons inside them, blanked off the holes, modified the crankshaft, made smaller, 3-cylinder-per-side heads, and then probably knocked off early to the pub. The result was a V6 engine that, seemingly by magic, takes up exactly as much room as a V8!
Here, have a look:
And it’s heavy, too! But not just normal engine-heavy: needlessly heavy, thanks to that big-ass chunk of metal hanging off the back of the engine, doing precisely, as the British say, fuck-all.
Because the block is the same size as the V8, the crankshaft has to be the same length, meaning that on that last un-needed journal is a balancing weight instead. The crankshaft also has split pins so each connecting rod can be separated, letting the spark plug firing happen at 120° of rotation. Remember, this block was designed for a 90° V8, and not the ideal 60° that’s preferred for a V6, so, you know, they had to get clever.
The bore is reduced on the V6 to 84.5 mm from the V8’s 92.5 mm, giving a displacement of just about 3 liters, compared to the V8’s five. The V6, with its supercharger nestled in the generous valley of that 90° vee, makes a respectable 380 horsepower.
Now, what I love about this engine is that it seems to be a near-universal source of bafflement to people, who are genuinely conflicted about how to feel about it. I am quite late to this party, and by no means the only one to find these compromises confusing. Videos have been made about it!
At first glance, it just seems lazy. They just blanked off the end two cylinders? Why would they do that? What possible advantages would you get in the car? None, right? More dead weight, more space taken up for no reason, compromises made for how the engine actually runs – what’s the advantage here?
And then you start thinking about money, because this is a British carmaker, after all, and they have a long and beautiful history of pound-pinching, and you realize that a same-size block means the same engine mount points, and that means you don’t have to re-crash test the V6 version of the car, and then things start to make a lot more sense.
I’ve even driven a car with this engine before, and driven it pretty hard, on a track, back in 2014 when I attended the F-Type’s launch event. That event let me drive, back-to-back, the V8 and V6 versions of the car, and at the time I was unaware of the peculiarity of the V6, which, I should note, was so disguised under plastic engine covers you couldn’t see the oddly short heads or anything like that, and during those drives I found I preferred the handling of the V6, due to the less weight up front. Now I know there could have been even less weight there! But you know what? I bet it wasn’t that much extra weight, probably 50 pounds or so.
But, significantly, I didn’t really notice anything negative – I liked the V6! It’s not a bad engine by any means, at least not in the context that Jaguar used it. If you were, say, to use it in a car that had no V8 option, it would get significantly stupider, because all the reasons that make this engine make sense would disappear pretty quickly, leaving you with an engine that was heavier than it needed to be, more complicated than it needed to be, and used more materials than it needed to.
Part of me just loves the eh-fuck-it engineering that went into this engine; don’t need the extra two cylinders? Just board them up! It’s like putting drywall over a bathroom door because you haven’t cleaned it in two years and it’s just not worth bothering now. It’s both half-assed and yet also pretty clever, given the circumstances. In short, it’s glorious garbage, I think in the best possible sense of the phrase.
Novice-wrencher question:
So is it a thing to buy the Supercharged V6 versions and swapping out the engine with an affordably sourced V8 version? If they sit on the same footprint, what else would need to be done to the car to get that to work? ECU tune? Would the rest of the drive train and accessories work without modification in, say, an F-type?
Probably a significant difference in the wiring harnesses between the two engines. It could be figured out but would be a bit of a pain.
I know they would never have done it, but I just thought of a way they could have done this in a more interesting way.
What if they had kept the v8 block, with all 8 pistons. Then changed the crankshaft and cam design for the two “unused” cylinders which converts both of those cylinders in to essentially a v-twin air compressor… acting as a supercharger for the remaining 6 cylinders.
Kind of like the old kits that existed to turn half of an air cooled VW motor in to an air compressor while the other two cylinders provided the power.
This way, JLR could have avoided putting on a separate supercharger and still had it “technically” be a forced induction V6 of the same displacement.
I don’t have any values to know it for sure, but I have read that a turbocharger has a turbine wheel spinning at tens of thousands RPM (I think it said 80k for a modern turbo). I doubt that you would feel much of a difference (if any) from two pistons pumping air at a lot less than 10k RPM.
Having had the distinct misfortune of having to work on one of these, they’re just as bad to work on as the V8’s. Garbage engines overall, with never-ending vacuum leaks and check engine lights. You wanna know what the book time is to replace one (1) valve cover on that V6 when the internal oil separator fails? 11 hours! At least, that’s what it was on the AWD Jag I had to work on.
I’m all for parts swappability. In M112 and M113-powered Mercedes, it’s a different block between the V6 and V8, but everything else swaps. Starters, accessories… it’s really nice to be able to grab parts off either in the junkyard.
Reminds me of the 486SX processor on 90’s PCs that was the same chip as the 486DX, just with the math coprocessor disabled by firmware.
They had to find a way to sell those expensive 80487 math coprocessors 😉
But overclocking was so much fun back then. I remember me and my friend borrowing nail varnish and stocking from his GF. She gave us the most pathetic look when we asked.
Similar to the PS3 where it received Cell CPUs that had reduced performance than the standard spec so they could increase production yields instead of having to junk them.