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#31
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Quote:
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Cheers! Scott McPhee 1987 300D |
#32
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Yes. Boost pressure is regulated by a spring irrelevant of the altitude. The turbo has to spin x times faster to produce the same boost at altitude than it does at sea level.
I was actually not 100% sure on this when I started writing the response but look what I found on google : http://books.google.com/books?id=pewyJ3_F4XMC&pg=PA105&lpg=PA105&dq=intake+temp+high+altitude&source=bl&ots=RmTX4mlej0&sig=VLCQOhxst-UEGx85Qswv5jy2uHQ&hl=en&ei=qzQ4TrCpHsa5tgfzzp3kAg&sa=X&oi=book_result&ct=result&resnum=5&ved=0CDAQ6AEwBA#v=onepage&q&f=false Second column, where it reads intercoolers:
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http://superturbodiesel.com/images/sig.04.10.jpg 1995 E420 Schwarz 1995 E300 Weiss #1987 300D Sturmmachine #1991 300D Nearly Perfect #1994 E320 Cabriolet #1995 E320 Touring #1985 300D Sedan OBK #42 |
#33
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Just a comparison...
I had my TE on highway 70 in Colorado a few months ago. I remember stopping at a rest stop somewhere around Breckenridge that had an altitude sign that said something like 9700'. The snow was about ten feet higher than the roof of the rest building. I was going to drive through Aspen but missed the exit, and there was nowhere to turn around till I got too far away. Anyway, my TE was struggling to climb those steep passes. I recall dropping to 2nd on one occasion to maintain 50-55 mph. I had to use 3rd on all the climbs. Once I starting approaching Denver people started passing me like I was standing still.. but then I would blow past them on the decent, I dunno why. I was happy to have snow tires since I hit a couple patches of ice out of the blue in the peaks. On ramps and relatively flat parts where no problem, the power felt the same and the mpg's were consistent. Only problem was radio reception, I didn't bring any cd's. On a side note: I drove from SLC to Indianapolis. It was my first time driving/being in that area. I have always loved mountains and that trip was a treat for me. I saw several places I would like to live but my favorite place was Grand Junction. I took some pretty big risks with the car. I was happy to explore remote areas that piqued my interests. Once on the other side of Denver I elected to take highway 76 towards Indiana. I detoured through the Pawnee National Grasslands. That is where I got the TE up to 110 mph without incident. I loved being in a remote area. I looked at my gps and decided to go even more remote.. I plotted a path through dirt roads back towards 76. I recall being 38 miles from the nearest paved road and another 40 some miles to the highway. My avatar was taken on those dirt roads. Sorry for the story
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08 R320 CDI current Past 95 E420 87 300D Turbo 5spd 90 300TE 83 300SD 85 300TD 92 400E 85 190D |
#34
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#35
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The "irrelevant of the altitude" assertion in not correct. At some pressure differential (altitude), further compensation will not be possible.
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#36
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I think you are correct but I'd need a more careful analysis to be sure.
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#37
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My take on the issue:
Higher altitude results in lower general PSI, less oxygen content per cubic of space and less mass of gas to move. Therefore, the engine would be starved of oxygen. Pumping more volume of gas into a smaller space as with a turbo would provide more O2 but also more of the other gasses as a percentage of total gas. Having less atmospheric pressure would mean that turbo would need to spin faster to pump a measured volume. I can't see the pressure inside the intake manifold being dependent on outside pressure provided the turbo can maintain the rated intake manifold pressure given the exhaust manifold pressure available. At the very least, it seems that the turbo might spool up more sluggishly. Given the 14-15PSI (i.e. approx 1 atmosphere at sea level) rating on these turbos, the only real variable would be oxygen content of air after full rated PSI is reached and maybe the ALDA. I don't see how an intercooler would really matter. Maybe only in allowing the pressure to drop due to lower charge temperature so that additional gas volume could be inducted.
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Codifex 1981 240D ChinaBlue (Got her running with a donor engine.) 1983 300DTurbo w/sunroof. 1984 300TD manual sunroof. (Electrical Gremlins) |
#38
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Quote:
That pretty much settles it: turbocharging just cannot work!!! Last edited by tangofox007; 08-03-2011 at 09:13 AM. |
#39
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While the process may be viewed in mechanical terms I suspect quantitative analysis would be based upon thermodynamics.
I love the field but seldom use it besides at a simple level. The turbo process may be modeled (I don't know for certain, Brian C or someone else will) as an adiabatic compression. If so than P * V^γ = constant where gamma (γ) is the ratio of heat capacities at constant pressure and constant volume. I'm neither claiming that is correct nor that I can go far with this analysis. Just saying the physics has some subtlety and the post above about inter-coolers was demonstrating that. Last edited by sjh; 08-03-2011 at 12:02 PM. |
#40
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When it comes to operating 240D's at high elevation, I suspect that it's the driver who is exasperated, naturally or otherwise!!!
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#41
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Turbos were basically invented for and first fitted to airplanes! Pretty solid case here why they are useful at higher altitudes, in cars too.
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Cheers! Scott McPhee 1987 300D |
#42
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As I recall most turbo aircraft start losing power at 19,000-20,000ft they wil still go higher and other benificial things start occuring as well with the thinner air. Less parasitic drag and cooler temps on the outside as long as you keep fuel mixes in the normal range allow faster speeds for less hp. It is also much easier to melt the engine in those conditions. My Powerstroke is very happy at any drivable altitude and it seems to pull harder the higher it goes(it has never been over 19,000 feet). It may be less frontal drag or cooler temps?? I do know the turbo spools quicker and has more of a hit. |
#43
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I live in SLC. I have not had my 300d at sea level (yet) but I have taken it to Snowbird (ski resort) approximately 4500 feet to about 8000 feet over about five miles. I see an approximately 10-15 degree rise in exhaust, and can only maintain 55mph with manual shifting the automatic transmission.
Day to day, the 617 Turbo is slow, but livable at 4500 feet, but that likely depends on what you are used to. Had I gotten used to this car at sea level, it may well feel emasculated at altitude. |
#44
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The other factor to consider is relative power. Since most cars on the road are non-turbo and are losing more power at altitude than a turbo car, the turbo car will seem much faster when driving with a group of non-turbo cars. I have no problems driving my 85TD between 5-10,000ft as long as the overboost control line doesn't come loose The 77 300D however, was a dog at those altitudes.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#45
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5k is nothing to a turbo engine. I regularly go above 10k without any problems and my engine actually seems to like it better!
These are just two of the pass pictures I have, I've also been to 14k at Pikes Peak and Mt Evans several times. My goal before the end of summer is to go over every drivable 10k+ pass in the state. |
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