Maybe running lean & driving like an old woman. But it's not representative. I'm from the petroleum industry & know every trick in the book to make misleading consumption claims. The XK lacks efficiency for many reasons too long to list.

 

I was going up and down mountains and going with the flow of traffic, which varied from 100-120 km/h. I certainly wasn't doing 60 km/h to try and hypermile. I wasn't driving for economy, I just got it. You couldn't have picked a worse route if you were trying for economy!

 

Maybe so but Harry Weslake warned Lyons that the long stroke, high piston speeds, long pistons, comparatively small bore which restricts valve sizes would always hamper the XK engine & advised against it. 100/120kph is actually a pretty economical speed for the S with it's gearing etc. Best aero of all the compacts. But likely running too close to stoichiometric.

Out of interest. Were you running EFI when you suffered your heat seize?

 

I suspect Weslake's views related more to achieving a lot of power more than efficiency. For efficiency, the problem of the XK is that the combustion chamber is quiescent and the spark plug is far from the centre. The flame takes a lot of crank angle degrees to reach the far side of the chamber. There are solutions: more turbulence from squish or a reduced/shrouded/throttled inlet valve. Neater and consistent with modifs of the time would be twin-plugs or asymmetric pistons. Put some of these together with an increase in compression ratio and mapped ignition and fueling and 30mpg, or at least upper 20s, might not be so far away. It'll not pass cost-benefit, but it would be fun.

After all that, it's still a big engine with large bearings in a heavy car. It's not going to be great in traffic. One thing that I've noticed with my Daimler V12 is that some up and downhill doesn't seem to harm the economy so long as I'm restrained on the uphills. It may be that with good fuel injection, the wider throttle opening on the uphill and the closed throttle going down work out well. I've watched it a lot as for ages I didn't understand why I couldn't achieve the target 21mpg at 80mph of the perfectly running series 3 V12. I eventually solved it: my speedometer reads 3 or so mph slow.

 

VW, BMW and others recently have been caught out fudging the MPG figures with complicated computer programs in their ECUs costing millions in development and now fines and compensation when all along all they had to do was copy Jaguar and bend the speedo needle back a little bit.
"Sorry Gov must have knocked it with me elbow when I were putting it together" the defendant told the court.

 

Yes ~ heads should be added to the long list. Weslake thought that piston speeds were ridiculous, was critical of combustion due to head design which as a combustion engineer & tribologist I agree ~ as do you, and valve size restriction due to bore by making the engine so undersquare.

His views related to both power & efficiency. Lyons wanted him to get them over the 20mpg mark in modest driving. Autocar's enthusiastic test of a 3.8 MOD S Type returned a miserable 12.8mpg (22ltr/100km). EDU 482C ~ Same car as Bolster tested. I suspect they kept it close to the red line much of the time.

Re other. Constant throttle always benefits economy. Of course more so with carbs with thottle pumps or the SU throttle pump effect due to the damper. Equally equivalent speed helps as you have found. EFI with fuel shut of, or near to, to maintain coasting speed downhill vs throttle opening to maintain speed uphill would be an interesting comparison to see what comes out in the wash. Constant speed vs constant throttle.

I have spent months on dynos running EEC, ECE, EUDC cycles & then taken cars on the road in urban, extra urban & motorway conditions & found little correlation.

 

BTW I've also tried to drive the ECE cycle manually against a head up display. Forget it. Can't get close & air density/IAT, gradient, tyre pressures & wind etc. etc. ruin any chance. Also tried to test friction modified engine oils off the dyno. Forget that too. Only way is on the dyno with throttle fixed & with all parameters measured & results suitably corrected.

One should also consider when it comes to power that it is no bad thing. One can choose to use it & suffer the consequences or back off and take it as improved economy.

 

Most likely, but I can't remember. I did the conversion quite early after I got the car on the road. The biggest reason was the starting carb was poor, and just the way my neighbouhood is laid out. I could start the garage , back it out of the garage and by the time I got the to main road the starting carb would shut off and then the car would stall on me right about when I needed to turn into traffic. It was frustrating to see the gap and the car would die.

Partly also it was the intellectual exercise, I wanted to learn more about EFI and doing a conversion like Megasquirt mean I'd learn a lot - and I did.

 

The reason I asked is that the cause of the heat seize could well have been the EFI running too close to stoichiometric. i.e. too lean & expanding the pistons into the bores.

Very common in racing two strokes when on the edge & running into oxygen rich air under trees overhanging the track or just plainly too lean. Pistons would look just like yours did. Bores would have the Nikasil torn off.

Have you any idea what your AF ratio was?

 

I had tuned it rich at the that point, so probably somewhere between 12.5-13. I had mapped it to only go to 14 under light throttle cruise. At the time I didn't have the VE table fully developed, so I was doing tuning; but had mapped it rich on purpose to prevent it going lean under most conditions.

 

Not the best photos, but here are the two pistons that scuffed. It was cylinders 1 and 4, so those were fed by a different injector, the other 4 pistons were unmarked.

 

Are those stainless steel sleeves, if they are, that's what caused the scuffing ?

 

In the real world unless specifically designed as lean burn engines with appropriate clearances etc. etc. your AF Ratio should never go anywhere near 14 to 1 under positive throttle (stoichiometric AF ratio approx 14.5:1 for gasoline/petrol). Certainly not an XK. 11 to 12.5 max should likely be a permanent target AF ratio for max economy & decent running. Those pistons & bores are typical over lean heat seize ~ pistons expanded into bore. An XK should probably produce max power at about 10.5 ~ 12 to 1 reliably on a dyno. Likely nearer the 11 to 1 mark at standard piston to bore clearance. ( guessing from experience.)

 

Sleeves are steel, not stainless.

As rich as 11:1? Everything I have seen says max power at 12.5 for a gasoline engine. I've not put my car on a chassis dyno and measured power though.

 

Is that the rearmost cylinder? The twin SU manifold has been accused of providing a slightly weaker mixture to that far end of the engine and the cooling system has similarly been accuses of not cooling it so well. A richer mixture lowers the temperature in the chamber and at around 12.5 (as you stated) gives roughly the highest flame speed and power. Stoichiometric or slightly weaker is good for economy under light throttle or would be if the chamber had a bit more turbulence ..

I tried (with cardboard cut outs and a tape measure so accuracy is limited) to see how a series 3 XJ injection manifold would fit on my Mk2. Note that my engine is slightly slanted with the inlet side high and the exhaust low, so it starts with an advantage. My estimate is that there's something like 2cm overlap with the steering column and a small overlap with the inner wing. The latter could be resolved with a little panel work and the steering column lowered out of the way (especially if there's a rack conversion also going on). However, my car is a 3.4 while the OP's is a 2.4 with a block that must be 7cm shorter, which makes the steering column much more of a problem.

 

Try it, Dyno testing is fun. But monitor at least IAT as it has a huge influence & can mislead you. Try & do it all in a couple of hours in stable ambient conditions. Try & find a decent Schenck or similar dyno. These roadside things are junk & float like hell. You might achieve peak power at 12.5 on a modern engine with all it's electronics, ECU, variable length runners, VVT & lift, sophisticated knock sensing & timing control, direct injection, better volumetric efficiency, reduced frictional measures & materials. combustion enhancing techniques, active alternators, higher compression, higher injection pressure & multipulse etc. etc. etc. ad nauseum ~ long list. These are just a few that come to mind, I'm sure I've left plenty out. Modern Mercedes Quadcam V engines with a combo of these achieve peak power at about 12.4 to 1. All these more aggressively used in the AMG's. I'm not considering turbo charging here because it's not a fair comparison. The little Merc 1600 cc V6 engines in their F1 cars have a thermal efficiency of over 51%. Our Jags are likely under half that.

I don't buy 12.5 on an XK with my time spent on dynos on a range of engines both new & oldish. Older designs need more fuel (richer mixture) for peak power. Some older Toyota & Nissan inline 6's I have run gave peak power in the low 11's.

 

Peter ~ the rear cylinder is no 1.

 

Sorry, missed the explanation above the photos.

Further to what you wrote on A/F ratio, log type inlet manifolds are not good at achieving a uniform mixture. Fuel sticks to the walls and droplets tend to go straight on most often into the nearest cylinder. In consequence, to avoid problems with a local weak mix, the average A/F has to be more on the rich side.

Modern direct injection, if working as intended, makes the mixture weaker in the quench zones (on walls and especially between the piston and cylinder wall above the top ring) and richer around the spark plug to facilitate ignition and initial flame growth. Thus, it has a rich mixture where it's useful, but a closer to stoichiometric one averaged over the whole charge and as required by the catalyst. Of course, there are down sides: reduced VE; more droplets and so more particulates.

Back in the day, there was competition between some of my contemporaries: stratified charge Vs lean burn. Neither side quite made it.

 

Yes. The modern F1 engines run a pre combustion chamber with the plug surrounded by rich mixture & lean mixture in the main combustion chamber itself. Started by Merc & copied by Honda as was the split turbo with shaft running down the V. I'm pretty sure Renault & Ferrari have now followed the pre combustion chamber route but are cagey about it. Split turbo tightens packaging for aero reasons & helps keep inlet air colder along with the intercooler.

Wholly agree with your comments on "log" type inlet manifolds. (Why I liked our twin, twin sidedraft Weber set ups on the Alfas we have both owned). Triple twin side draft Webers also worked well on the Aston Vantage engines.

 

And I was tired when I typed the numbers last night and got it wrong. The scored pistons were #6 and 2.