free hit
counters
hovgaard - The Lotus Forums Jump to content

hovgaard

Basic Account
  • Content Count

    370
  • Joined

  • Last visited

Community Reputation

2 Neutral

About hovgaard

  • Rank
    LOTUS
  • Birthday 16/05/1971

Contact Methods

  • Website URL
    http://www.xdin.com

More Info

  • Name
    Jens Pedersen
  • Car
    Esprit S4

Recent Profile Visitors

1,962 profile views
  1. Thanks, Marcus, you're too kind! Bibs, maybe I was a bit too harsh on your planning skills, but my advice still stands. I wanted to stress the importance of matching the turbo to the engine you want to end up with rather than the one you start out from. Talking to someone in the know is always a good thing, but even I can tell you that the oem solution was to a large extent governed by product cost, a statement informally backed by Garrett people. One thing that I think perhaps we should elaborate on is surge margin, as I have noticed that there are quite a few hybrid turbos available out there for our cars. The basic idea of a hybrid turbo is to combine the high flow capacity of a large compressor with the response of a not-so-large turbine. That sounds wonderful, but there are at least two distinct drawbacks. 1: Assuming that you have a fairly large air mass flow (a fair assumption considering that this deals with large compressors), that large flow must also pass the turbine section. Since the turbine is relatively small, a large portion of the flow will be going through the wastegate, it just won't all fit in the turbine. In order for the small turbine (operating on limited mass flow) to generate enough power for the compressor (which will be consuming plenty of power to compress all that air), we must have a very large exhaust manifold pressure. In other words, the turbine/wastegate combination can be seen as a turbine with extremely poor efficiency, even if the turbine itself can be demonstrated to have good efficiency (something we can only benefit from lower down in the engines speed range where the air consumption is smaller). It may seem counterintuitive at first that a large wastegate flow leads to a large exhaust manifold pressure. Ultimately, your engine will make more top end power with a larger turbine. 2: With a relatively small turbine, we will still get good response (say, similar to oem spec), i.e. we get to combine good boost and a small air flow. Now, a centrifugal compressor can only have so much map width, and as we go up in size to get increased flow capacity, we also loose its capability for boost at small flows. Of course, we can have small flows going through a large compressor, but not while making boost. The larger the boost pressure, the larger the flow must also be. Too much boost and too little flow at the same time leads to a highly undesirable condition known as surge, where the boost pressure fluctuates uncontrollably as the compressor blades alternate between stalling and regaining composure. This can be detected as a series of loud bangs or whooshes in rapid succession or it can be detected by the vibration of the boost gauge (a good business case for an *undampened* boost gauge (which can be annoyingly noisy even under normal operation due to pulsation from the intake valves opening and closing)), and prolonged operation in this regime can damage the turbo. Also, I'm not sure the ecu can keep up and maintain lambda. Change down a gear if it ever happens! - and remedy the situation at your earliest convenience. If you look at a compressor map, you will find a sharp border, known as the surge limit, above and to the left of which he who enters should abandon all hope. The problem of surge can be combated to an extent by electronically limiting the boost at lower to intermediate rpms, for instance by means of a custom ecu calibration. Given the compressor map and the engines capacity for swallowing air or given a hand drawn boost curve below which you can't detect surge, and given enough money, I imagine it would be fairly easy for someone like Marcus to make such a thing. However, boost pressure cannot be electronically limited to a value below the turbochargers basic boost level, which is largely governed by the choice of wastegate actuator, and is usually around half a bar. Choosing a softer actuator will make it difficult to accurately control the higher boost pressures and is not really advisable in this context. If electronics don't solve the surge problem, you need to better balance your turbine size and compressor size (i.e. select a larger turbine). The closer you can go to the surge limit, the better response you can give the turbo and the wider the speed range you can give the engine. Cutting it close requires tight control over the engine, and you will want at least a small surge margin. This does not mean to say that hybrid turbos are inherently a bad thing, they're not, they have their place. It just means to say that when buying such a product, you need to know what you are doing (or at least the supplier needs to know it intimately). I hope this illustrates the importance of compressor maps and knowing where we are in them. Furthermore, I think it can be seen as a business case for someone like Marcus to provide kits with a turbocharger and a choice of custom chips to match, and a higher spec kit that also includes, say, a green dot cam pulley and a large charge cooler and whatever else he decides on. But to make the most of it he would have to depend on the discipline of the owners to stick closely to his spec. Can we be trusted to do that? BR
  2. I have been asked by a fellow forum member to give my take on this thread, and since I hold him in particularly high regard, and although much of it has been said by others, I will do my best not to disappoint him. So, in my hallmark condescending tone of voice, I plunge myself into the flame wars. First, I'd like to comment on a couple of minor issues early in the thread. I too do not think that it is advisable to restrict the oil flow on a journal bearing turbo. DanR raised the very valid question of internal vs. external wastegates. An external wastegate is preferable, because internal wastegates tend to make a mess of the flow around the turbine wheel, which may significantly reduce its efficiency (some turbines are worse than others). When we are using the wastegate, we are trying to make a lot of power, so that would be an opportune moment for good efficiency. The argument that the wastegate is there to reduce turbine power anyway is not valid, because with greater turbine efficiency we would be able to open the wastegate more, to get lower exhaust manifold pressure, which is good for engine pump work and cylinder emptying alike (meaning less crankshaft power is expended during the exhaust stroke and more fresh air is sucked in during the intake stroke). Furthermore, an external wastegate lends itself to interesting things. Depending on your preferences and requirements for emissions and sound, you can choose to reintroduce the wastegate flow into the main exhaust flow in a number of ways. Put it in upstream of the cat and you are always emissions and sound compliant. Put it in upstream of the muffler and you are always sound compliant, but the pressure drop over the cat is much reduced. Or just dump the darn gas! You can run fairly high power with a stock cat (and be clean for the vast majority of the time), the pressure drop over the muffler is also reduced, and you get a clear audio feedback on the boost. On my S4, if I ever decide to change the turbo, I want to get a V8 thing-under-the-bumper, and make a wastegate tailpipe to the left. In the unlikely event that I decide it is too loud, a small muffler can be added. Incidentally, this is how aging P911T's work. The main issue here, however, was turbocharger selection. This is part science, part black magic, and part luck; with skill and experience, informed choices may be made, but the only way to be certain is to experiment, preferably using well designed and executed procedures, so as to ascertain the relevant data and to eliminate the sources of error as much as practically possible. I, too, feel that it will most likely be impossible to declare a clear winner even in a well controlled experiment, as the choice will be highly dependent on personal preference. When speccing a turbo, we always need to make a compromise. We should balance at least the following: * Reliability (refers unpredictable failure) * Durability (refers predictable failure or life expectancy, not to be confused with the above) * Physical size restrictions * Response at various engine speeds (I prefer that term over lag or spool-up) * Power or torque at various engine speeds * Fuel consumption * Product cost * Plus whatever I happened to forget Each person will have different priorities, and different goals leading to a different setup of any number of things around the car, so one person simply declaring one turbo the winner on one car would certainly be interesting to hear about, if nothing more. Some people might favour the cost and reliability of journal bearings, while others favour the response and efficiency of ball bearings; and so on. For the time being, all that seems to be available to us are a few compressor maps on the suppliers websites. We may attempt to compare them (we notice that WC has swapped the axis labels around), and it seems to me that, perhaps, the WC compressor sizes are slightly larger than PUKs at the same stage numbers. But not only are the maps quite different in graphical style, even if they were not, they wouldn't be truly comparable unless they were produced on the same flow bench by the same technician (for example, I would argue that the surge limit is a matter of opinion). There are no turbine maps to compare, but then, turbine maps never did say much to anyone anywhere anyway. There is no telling the response. The data at hand is grossly incomplete. We must experiment, and I too would hope for the suppliers support, since I feel that they are currently asking us to buy expensive hardware of which nothing much is known. Appallingly, the higher spec products don't even come with compressor maps. Ideally, I feel that the proposed experimental comparison should also include something out of the GT28R range as seen on http://www.turbobygarrett.com/turbobygarre...ts/catalog.html. This would be a bit more involved to do, however, as it is not a direct bolt on fit, but on the other hand, part of the range lends itself well to the external wastegates that I like so much. Probably overkill for this thread, but it would have been interesting all the same. Personally, I am biased towards preferring good turbocharger response and broad maps. I would tend to be sceptical of clipped turbine wheels and compressors with no maps; and, while flow capacity is nice, I would want a reasonable surge margin. I don't subscribe to the viewpoint that the highest power number at a single rpm number on a dyno run wins, rather, I want the fastest real world car, and that does require good response and a torque curve somewhat wider than the space between gears. For that reason, I think that lap times on suitably fast track should be a prominent feature of the experiment. I think the testing should be done during a period of particularly stable weather to get fairly similar running conditions for each turbo. Meteorological data should be recorded; and tyre pressures and fuel load and all that stuff should be kept the same. When on the dyno, you should, as a bare minimum, record power and boost as a function of engine speed in a tall gear (4th seems like a sensible choice), and also try to record the boost as a function of time when idling at an intermediate engine speed (say 4000 rpm) and slamming on full throttle, to get some sort of comparable turbo response times. If you get all ambitious, you also measure the air mass flow as a function of engine speed (if you can), as this will tell us where we are in the compressor map, which in turn allows us to read theoretical compressor efficiency and surge margin, which tells us a lot about how well matched the turbo is to the engine. If you can find a dyno that can do this, then it is well worth travelling a bit to get there. Also, please try to record the compressor discharge temperature as a function of engine speed at full load (the silicone hose should seal well enough even with two thin wires between the charge cooler and the hose). The higher the temp, the poorer the compressor efficiency. If you get even more ambitious, you also measure pressure and temp before and after the turbine, so we can determine the turbine efficiency (and ultimately the turbo efficiency), but that requires drilling into the exhaust manifold near the turbine, which may not be to everyone's taste, although it affords a perfectly useful pyrometer instrument in the car afterwards (just don't use el cheapo temp probes that break and mess up the turbine wheel). In a professional setting, well over a hundred engine parameters would be recorded, but we also need to stay practical here. With some experimental data, we might better be able to make informed choices. Now, do I think that would help Bibs in his quest? Well, there is no telling, really. I mean no disrespect to the honourable Bibs whatsoever (or to anyone else for that matter), and I admire his initiative and dedication to our common cause that shows up yet again here, but having read this thread, it seems to me that he may be suffering from PLE syndrome (planless engineering). This is an all too common ailment amongst amateur car modders. "I'll pick up a few goodies and bolt them on, that should make me faster", seems to be the way the majority of these people think. While that theory may well hold true, it is not the recipe for achieving anything resembling an optimum, in which all parts come together in well-matched harmony where no single part is particularly overpriced and overspecced (or underspecced for that matter). What he needs to do is to come up with some concrete realistic goals and a budget to match. This can then be broken down into a coherent plan, and that plan can then be executed. This doesn't have to be something fancy enough to be presented to a board of directors, just scribble something down, but do include the whole car in the process, and make your choices with the greatest of care. Like, for the engine, you might say, I need so-and-so much power, with fair response and torque and whatever characteristics you prioritise. To achieve that we somehow determine that we need, say, a bigger charge cooler, a chip, some injectors, some cams, and a turbo to match. Tally up the cost and compare to the budget. This may be an iterative process, and for something as complex as an engine, professional advice by someone experienced in our particular engine and without further financial stake in the project may be well worth it if you are serious about what you are doing (i.e. don't just ask the guy selling you the parts)(btw I'm experienced enough in the art of engines to realise that I'm not qualified for this). Then, and only then, go out and buy all the stuff you need and bolt it on. Don't do what the proverbial Bibs is doing. Suppose he chooses his favourite turbo and puts it on his car. Then, a few months down the line, he decides he wants a bigger charge cooler. And so on and so forth. And before he knows it, that expensive turbo of his, that was determined at great pains to be the best available, has become a complete mismatch. Don't embark on your 400 bhp project by first perfectly matching the turbo to 300 bhp. I know this goes against the popular view that tuning comes on in a number of stages, but that is the way I see it. This methodology is called project management, and it is there to get you the most bang for your hard earned bucks (or quid or whatever you use) through minimizing the number of hasty choices and regrettable purchases. While it cannot guarantee that you get the very best available turbo for your finished package, it can certainly increase the likelihood. Good luck and best regards all around!
  3. This is how the Europa S should have looked.
  4. Why would you want to do that? Generic oxygene sensors are cheap nowadays. You don't need a Lotus specific item. Not having tried it on a Lotus, I would guess the ECU enters a limp home mode, running overly rich to be on the safe side. This leads to rough running, high fuel consumption, smoke, and the oil film on the cylinder walls is washed off. Not very recommendable in the long term. EDIT: Just read your EBPV post. 20 slow miles shouldn't do damage, just get the sensor fixed asap.
  5. The chips are here: The Chip link I used the Spax shocks on my 1989 Turbo. They are alright, but the range of adjustment is ridiculously large. It goes from 'Ford Lincoln' to 'unsprung' in about 14 steps, so it doesn't really fine tune. Oh, and don't repeat my mistake of putting the adjustment knob facing outwards. When you put the wheel back on, the knob is all but obscured. Turn it to 'Ford Lincoln' and then count clicks. As I recall, I used 12 clicks front and 11 clicks rear for street driving.
  6. hovgaard

    John Lennon

    It was Chapman who murdered Lennon.
  7. I would not consider the Elise and the Speedster to be the same car. The Speedster Turbo is cheaper and turbocharged, both of which make strong selling points with me, which is why I lust for the Speedster Turbo more than for the Elise. The Speedster is also heavier I think, and is said to have more docile, balanced, and predictable handling. Have yet to try it myself, though. Disregarding price, I would probably prefer the Europa over the Speedster.
  8. Carl's looks a bit fragile... Michael Rodrigues' does not; it looks perfect.
  9. It seems to me that Lotus has made a very nice commuter car, with the turbo engine I wish was available in the Elise. I would buy one as an everyday runabout if I was loaded, but it would never be my sense-of-occasion primary sportscar. Main competitor could be the Opel Speedster/VX220, though I don't think that is made anymore.
  10. That car is much nicer than what Slade was asking about.
  11. I do simple stuff myself and intermediate stuff with the help of friends. Main problem for me is that my garage is unbearably small, so large or difficult jobs is left to the independent mechanic about 25 km away or so. He is a one man operation specialising in British sportscars, although he will also do the odd old Alfa or whatever else comes along, but nothing mainstream. I like him. He claims the Esprit is his favourite thing to work on. I bet he says to all his clients that he likes their particular cars, but he does own an SE that he is fixing up after it was bounced between the rails on the Autobahn. Parts I have ordered from the UK. I don't use the Lotus importer, neither for parts nor labour, for three reasons. They are expensive. They are about 400 km away. They recently moved to a new location and rumour has it that that led to a high turnover of staff and that the new ones are inexperienced with our cars. A few years ago, before the rise of good forums, I was briefly in contact with the Danish importers to ask about some problem I had. They said they had only held the agency for four years, and had yet to sell their first Esprit, so they were unable to help with my query. These are the only two Lotus dealers in the nordic countries, and they are less than 100 km apart. It seems that it is difficult to maintain a competitive and competent service organisation in such extremely sparse markets, which is understandable, I suppose. It probably ads to the mystique.
×
×
  • Create New...