According to "Jaguar the Complete Story" It's the Ford engine with a 3 stage intake, variable valve timing and various other Jaguar tricks from their V8 line. I cannot find the section that talked about the engine being the one Ford wanted for the X line so the Jag engineers started with the block and added all their own stuff from the block up. Don't trust my bad memory so, maybe some other poster can verify that. So what I remembered from the description of the X's engine was it's a Ford block and all the rest is Jaguar engineering. This could be why Jag says premium fuel and Ford does not. I am not sure how intake and valve timing can affect fuel requirements VS the standard Ford intake and valve timing.

 

This is more myth and misunderstanding. High octane gas contains no more 'energy' than any other grade, nor does it burn 'cleaner'. All gasoline comes from the same base stock. High octane gas has an additive package that helps prevent detonation/pinging/pre-ignition. That's it.

 

The AJ6 engine was designed as a collaboration of Porsche/Yamaha. Purchased by Ford, minor changes were done at Coventry in England for the X-Type. 'Minor' meaning mostly ECU changes after adding an additional 0.5L of displacement and higher compression for a little more power. Other than that.... pretty much a 2.5L found in the 99+ Mercury Cougar, Ford Contour and Mercury Mystique. BUT, the higher compression should necessitate higher-octane fuel. A very durable little transverse-mount motor, could likely handle 6-8lbs of boost regularly if it weren't for the world's most nefarious transmission. a nice mercedes AMG-derived 5-speed paddle shifter trans would be ideal if we were RWD.

 

Jaguar modified the Ford V-6 to run higher compression, that is why it requires higher octane. US minimum should be 91 R+M

If you use lower octane you will not feel or hear it, the computer retards the timing to prevent knocking. This is still not healthy for the engine and can lead to shorter engine life.

 

Thank-you Gold_04_X-Type for solidifying my prior post.

 

Care to provide a technical explanation behind this and back it up with proof? This discussion goes on all the time on this board and others, with dire but vague predictions of terrible outcome based on nondescript reasoning, yet nobody's ever seen an example..........

If the computer retards the timing to eliminate knocking, why would the engine become damaged? Yes, it will produce less power, and get worse mileage but how/why would damage still occur?

 

There are an awful lot of misconceptions out there regarding fuel, mileage, octane, anti-knock properties and a host of other components of gasoline. Sit down with a couple of cold beers and educate yourselves with the attached document. Pay particular attention to pages 3-10.
I have squashed more than a few arguments, scratch that, disagreements, with owners regarding spark knock and engine performance after insisting they read it.

 

I can further validate that particular attachment after discussing just such an issue with a neighbor who worked for BP Technology and Development.

 

Quid pro quo, if I may.

There seems to be a tone of dislike and/or distrust of the higher grades. Why is that?

 

I don't think it's dislike or distrust. It's simply, if you don't NEED it, why pay for it.

 

I think I tagged the wrong response as to why I asked that question. The following is the one I meant to tag. Especially the first sentence.

Perhaps I'm reading too much into it.

 

I believe the best answer is that the RISK of damage is much greater. I tried to convey in an earlier post, there is a limit to the ignition retard the ECM can provide, let's just say 40 Deg. for example. If running on the proper octane, in theory the timing will seldom have to be retarded. Now let's put lower octane in there. Again, in theory, during normal driving the ECM will have to do much more retarding to compensate. Let's say it has to regularly retard 18-20 Deg. to cover for the inferior fuel. Now you want to pass or pull a hill. Now when you crowd the throttle and the ECM needs to handle the spark knock, it might need to retard 35 Deg. to protect things. On the inferior fuel, it's already at 20 Deg. retard, it needs 35 Deg. to handle the detonation. Guess what, you don't have it when you need it most.

That is maybe an over simplification, but it makes the point. Use the octane they specify. They know what it needs!

 

This actually started with a comment I made about using higher grades on two cars that I don't drive much. It started in a previous page of the thread.

 

I've seen similar documents from other sources and am in occasional contact with one of the contributors, so there's nothing new in this version for me. My comments come from 31 years of first handed experience in the engine design, manufacturing and support business (and an additional ten years on top of that playing with hot rods and bikes).

Your example above doesn't relate to how engines actually operate. During normal driving NO retard is required- as the engine is not anywhere near the threshold of knock, even if run on low octane. Typical timing adjustments required to eliminate spark knock are in the order of 2-4 degrees, not the 20-40 degrees quoted. Let's say 5-8, in an extreme case just to be safe. Do you have hard evidence that the X Type engine cannot provide that degree of adjustment, or are just guessing the same as the BP guy? There are a few owners who use regular gas and report no ill effect. Are they wrong?

I have no like or dislike of any grade of gas. The OP asked a technical question and deserves an accurate correct response, nothing less. I once got caught out having to use 87 octane in one of my other cars that does require 91 or better and has NO computer to retard the ignition and yes, the ping was alarming but easily manageable by not putting my foot in it too deeply.

It's very easy to predict that 'the sky will fall and bad things will happen', based on assumptions, theory and third handed information but let's deal with real life.

 

 

Hey Bond, what is your source for this info?

 

We all can afford Jaguars. If Jaguar says to use premium I am sure their is a logical reason. So I use 93, all I can get here. I am also interested in learning more about this collaboration of Porsche/Yamaha for the AJV6. Never heard this.

 

http://en.wikipedia.org/wiki/Ford_Mondeo_V6_engine
2nd sentence: "The Mondeo V6 is a modern aluminum DOHC V6 with a 60° bank angle. The primary engineering input came from Porsche, who were developing a similar V6 before selling the engineering to Ford, and Cosworth, who helped with cylinder head manufacturing.The Jaguar AJ-V6 engine is similar but adds variable valve timing. Mazda's AJ version also has this feature."

 

When I can't get 93 or 92 octane, I'll dump a half a tank of 89 into my cat. I'll also stop at the local Wal-Mart and pick up an Octane booster. At the same time I don't loose any mileage the best I've gotten so far on the highway was 34 MPG. I don't have a problem with that mileage, just wish I got that all the time. But nobody said Jaguars were a cheap car to run.....

 

Ding ding ding...winna!!!!

I use 89 most of the time but I'd be willing to bet that at 87 it would be fine. I have when the only pump available was 87 filled it. I drive with the window open a lot and actually listened for a ping....nothing nada. AND I got better gas milage with the 87. It's all smoke and mirrors. It's like ethonol, there is such a minor trace that it's really just gas, the rest is marketing.