Turbocharger

Bristol had enough salt on the roads to make it look like a gravel rally stage. I wish I had windscreen washers...

I see your point. I was thinking that the stresses would be several orders of magnitude greater, but then it'd just tear the thing apart of course. On further thinking about my idea of rotational vs cross-axle loading I don't think the loads are rotational any more either, so that knackers that idea too. In fact, I'm going back to buses. A few kg here and there doesn't make any difference

I'm with you on that, but my thought train is thus: In braking/accelerating, the axle's trying to rotate and the hockey stick resists that with both bushes - they share roughly half the work and they both try to deflect the long straight part of the stick (the 'handle' of the hockey stick') into a curve. This wouldn't heavily load the area between the bushes where we've seen the failures. In cross axling you're trying to rip one or other mount off the axle, and this fully compresses the bushes vertically in opposite directions. This puts a curve in the handle of the stick in the same way as braking (well, one in each direction), but there's a big bending load in the curved part of the stick too. I'm quite willing to promote intelligent discussion like this though - I've never dealt with Mr Marsh but if he plays his cards right, a solution might present itself on here for free from some free consultancy group thinking. Until he suggests his chosen way forward it's a little premature for any of us to start pointing the finger.

It shouldn't be hard to make your own CAD model - two flats for the top and bottom of the arm, a flat with some holes in it for the web, two tubes for the bushes at the axle ends and some curved flat + profiled web for the area between the two bushes. The issue with making a model and running it through FE is the same as Dave Marsh has had when he's done his own stress analysis - either by computer, on paper or in his head (and I may be doing him an injustive by assuming it's the latter). The issue is that we don't know the loading case and material properties accurately enough. The model will only tell you what we already suspect - that the fatigue life of the material between the two bushes isn't enough for the work these vehicles see. I'm not certain that Mr Bish is 100% on the nail, since my feeling is that cyclic road loads won't be as significant as cross-axling, for the reasons that HFH gives above. Offroad, as one wheel lifts and another sags slightly the stress on the bushes is massive. On the road, the load that dominates these arms is bending as the hockey stick stops the axle from rotating under braking or acceleration forces. OK, the failure is fatigue and that means a lot of cycles at low stress but my gut feeling is that the offroad condition (fewer cycles but at much greater stress) is more significant than on-road loading.

I bet the Bentley's on best behaviour since it saw the Disco get cut up for a minor transgression... Actually, that'd be a monster engine/gearbox combo on Megasquirt.

Thanks Paul - always interesting to see how other people live - as you say there's a lot we could learn from the sense of community, but also it's notable that wood-fired central heating is close to zero-carbon in operation, so long as the woodland is sustainably managed (and I can't see that it wouldn't be). Chilly in Bristol today - minus 2 degrees this morning

To me the design of the arms looks ok. They'll only be loaded in bending (either by cross axling or by acceleration/braking). The single nut at the chassis end means they can't be twisted (loaded in torsion) so the discontinuous welding between the two plates and the web shouldn't be a problem. Equally, the holes are along the neutral axis so shouldn't be in a stressed area or heavily affect the bending strength. Since the failures pictured on here (I haven't seen the Pirate thread) are around the 'hockey stick' bit, I'd guess there's an abnormal loading around there, and that LR put enough (forged?) metal in there to resolve the situation. As was said earlier, time to wait and see how QT respond on Monday.

No, I mean vanes - there is no wastegate. The vanes are sized such that the turbo can flow all the gas from the engine without making mega-boost, so it just opens up instead of having a wastegate. Good point about measuring pressure though - I have a pressure tapping on the back of the inlet manifold and this feeds the dash gauge, injector pump and diaphragm by T-pieces. I now suspect that the pipe onto the manifold is leaking so I'll replace it with a tighter fit tomorrow. Of course, everything wants a different bore of pipe so I need hundreds of adaptors or keep pushing pipes inside other pipes etc.

More playing today, and possibly a conclusion that I'll look into tomorrow. I tried to alter the length of the spring so it would pick up from the stop at lower boost, but reducing the free length by clamping the coils increases the spring rate, so this sends its operation in the wrong direction entirely. I put a new linkage together with my pigeon welder (but no mask, so I used the look away & squeeze trigger approach - it'll do for now). On a road test it shows 1.5bar boost at peak (it goes well ) but heavy surging again since the diaphragm doesn't move, even at that pressure. In answer to Bush65's point above, I made a video showing the force required to move the vanes. The answer is, just about none (which is lucky, it makes the maths easier). Next I went back to basics with the diaphragm, cut all the cable ties to return the spring to its original length and made a bench test setup to see what it does. The answer is: 1 bar = 7mm travel, which should be what I need to make the car work. So: I have a linkage which is tight and doesn't have any wobbly slack any more the vanes don't need any appreciable force at low loads, so probably small amounts when under load The diaphragm does what it's supposed to at sensible pressure levels, on the bench I think the last point means that there's probably an air leak somewhere, so I'll repipe it tomorrow and have another go.

I got a new stereo for the Ninety with a built-in microphone for bluetooth handsfree (which will probably be useless) but it also plays MP3s from a USB stick so no more skipping CDs Si - The RepRap looks excellent fun - Adrian Bowyer was one of my lecturers at Uni.

First thing you'd do would be to throw away your catalysts and particulate filters. A number of the current technologies use exhaust heat to enable exhaust catalysts to trade off the oxides of nitrogen (NOx) with carbon monoxide (CO). For example, the exhaust gas recirculation reduces NOx (because it replaces oxygen in the cylinder and interestingly has a high specific heat capacity so the charge doesn't reach the very high temperatures required to form NOx) but CO goes up - but CO can be tackled in a catalytic converter. Catalysts generally need tobe kept hot to work well, hence post-injection allows fuel to burn down the exhaust. Some heavy duty vehicles even have a seventh injector in the exhaust upstream of the cat! Unfortunately both of these increase the fuel consumption (and so the CO2 emissions) - until maybe three years ago this was less of an issue but the argument is now becoming "local emissions or global emissions" and arguing against the tiny reductions in harmful tailpipe emissions by large increases in CO2 emissions is rather pushing against an open door among engineers.

Thank you both. John - it hadn't occurred to me that the vanes might not be balanced, so I'll have to think about that. You're right about the single gas path though - the vanes are capable of opening so far the turbo won't generate any boost at any speed or load, so it doesn't need a wastegate to throw any gasflow away. James - you're pretty much mirroring my thoughts on what I can remember of control theory. I need a quasi-static response that follows the orange line, and then hope that this gives a sensible dynamic answer (or one that I can damp by clamping the tube to slow it down). Just damping it like this should sort out any problems because the feedback (moving vanes affect the boost that's generated, that moves the diaphragm that moves the vanes) should stabilise it in time. Given the number of things that can affect it, I think a number of springs and a bit of trial and error is in order

i just bought one of these too, the £12 Tesco 3W one. As Tony says, definately bright enough, it puts a 6ft circle on a hedge at 200ft where I wouldn't expect a similar size torch to reach the hedge, never mind with a defined circle projected. The 4W D-cell one at £18 might be worthwhile if you regularly guide aircraft in to land but I'm happy...

James - I think you're right, but I don't think it matters here - at least not yet. I'm not into the realm of tuning the transient response yet, I just want steady state results. Question is: what response am I aiming for? Julian's VGT Td5 suggests that I need it to move gradually from 0.5bar to around my target pressure, and then use the diaphragm's adjustable preload to fine-tune the liftoff point, and use the adjustable linkage to set the zero point. I think (hope) that good transients will come out of this naturally.

The Td5 is more powerful, easier (quicker) to tune and will probably give slightly better consumption if you drive it sensibly. I say, if you can live with the "lack" of power of the 300 and you don't want the 'as standard' toys on the car like active cornering etc then take the older, simpler vehicle.

What, no chrome? Nice build - you realise the rest of the LR has to be up to this standard now, don't you?

I can better show my question now. The spring I have is 60mm long and 22 N/mm (don't ask me in your furlongs and cubits). That's the thin black line on my graph, and it doesn't start moving until nearly 3 bar so it won't work. Question is, what do I want? The green box shows my working 'area', 0-1 bar and 0-7mm stroke on the VGT control arm. The purple line suggests a spring with no preload, which would start to open the vanes as soon as it made boost. Spring 37mm free length, rate 24N/mm, zero preload. The blue line is the same spring as the purple line but with some preload. The vanes don't move until 0.5bar, but it needs 1.5bar to fully extend the vanes. Spring 37mm free length, rate 24N/mm, 5mm preload. The orange and red lines uses less stiff springs with much more preload to get the working range in the right place. The effect of these is to compress the operating pressures so that nothing moves until say 0.9 bar, and then hits full extension by 1.1bar. Spring length 60mm, rate 8 to 10N/mm, 23mm preload. My question is - which do I want? (The secondary question is "can I achieve it with the springs I've got?" although I suspect the answer is no since I need a shorter spring, and cutting mine will increase the rate excessively).

Thanks both. I did the maths as John suggests before I posted, and I understand that a conical spring has a rising rate. I can see that I need to make the unit "stroke" around 1 bar (since that's the level of boost I want to run). My question is - do I want it to start moving as soon as any pressure's generated, or to select and preload a spring to move fully through its stroke around 1 bar.

Right, my two questions above have been answered by the day's driving: the oil drain is fine since it hasn't seized the lack of water is fine since it hasn't caught fire Now I'm wondering about springs to go in the diaphragm. In the diaphragm that Julian supplied there is a conical (progressive?) spring, and I've got another from a spare diaphragm (not shown) - ignore the scribbly diagram underneath, that's from something else: In my mind I'm aiming for this logic: But when I took it for a test drive, it doesn't move at all under boost. Some playing with an airline, a pencil and some scribbled maths bring me to this conclusion: Which says it doesn't want to move until 3 bar or so with either of the springs I've got. The minus 23 mm is the distance that the spring is pre-loaded by screwing it into the diaphragm housing. I can increase this pre-load further by turning the adjustment screw that Julian's provided for me, but this diagram shows that'll send it further the wrong way for the springs I've got. The tools I have are: adjust the end stop to preload the spring (make it shorter) chop the length of the springs down (but this will affect the rate) pick a weaker spring so it picks up off the end-stop at a lower pressure I think the third option is preferable, and I think the my logic diagram means that I need it to sit still until nearly 1 bar and then extend fully - in practice it'll find a middle ground because extending it will reduce the boost that the turbo is producing. I'm in head-scratching mode now, not sure which way to go with it.

There's a snippet for the Tech Archive if ever I saw one - very interesting, thanks very much!

Right, a day's holiday booked and all the Chrimbo shopping done, so the new turbo's back on (I'll be the first person to wear out a set of manifold studs at this rate...), and Julian's diaphragm looks very sexy on top: I bought a new oil drain hose to take the oil away again, replacing the cobbled-up one with a join halfway along it. Pirtek made me exactly what I wanted (and charged me £40 for the pleasure). It sits near horizontal at the lower end which I'm a bit worried about, but this seems to be the best balance to stop it kinking where the arrow shows. I tried trimming the length, this is best. Will this work? Now for the water cooling: Pirtek cobbled up this 10-16mm adaptor for the water hose by crimping some thick-wall tube to replace my copper B&Q reducer, but I'm not really happy with either. John's link to info on the Garrett VGT suggests that their turbo has water cooling for applications where a heavy manifold will store heat and soak it back to the turbo on shutdown. Mine's just made of thin tube so this shouldn't be an issue - which solves the water cooling issue. Am I just seeking an easy answer to the problem? Anyway, I'm quite ashamed that this is pushing on for a six-month project but I should be playing with the springing in the new diaphragm tomorrow.

I've got a cage, it's the soft-top that's causing the headaches. I can visualise something with a slit in the hood and a number of poppers around where it currently sandwiches the roof, but I can't see how it'd be very neat.

Reading between the lines here (and I've had a drink so bear that in mind) - you pressure washed your truck thoroughly and now you've got a noise which sounds like a slipping belt when you put the PAS system under load, but you don't think it's the PAS belt?

Probably worth mentioning that the brake pedal (and clutch?) will fail the MOT without a rubber non-slip surface.

I'll pick up the OT answer and then we can get back on topic... I like it in the following situation: Imagine driving up to an obstacle such as a kerb or rock. Manual car has revving, clutch-slipping and then bursts over the kerb and you need a third foot to brake before you career into the abyss beyond it. Same thing in an auto means you can just pick up the revs with your right foot, no friction elements to wear out as you just heat oil up and deliver a rising torque to the wheels until you overcome gravity, with your left foot hovering over the brake to catch the car when it leaps forward. It's not so good with engine braking (although I haven't found it to be an issue) and it's certainly not as good on fuel - I went from 28mpg to nearer 20mpg, although I think mine's undergeared at the moment. Some will rave about their manuals, some prefer autos. I like mine although I might have to rethink the decision if I can't get the mpg back up before it becomes a daily drive again. There's a not-quite-back-to-back comparison videos of a manual Td5 Disco and my 300Tdi auto Ninety on Stanage - I like the control that the auto offers offroad.