Friday, Nov 14, 2014 at 00:46
Hi Gary,
I trust some of this is relevant for you.
I lived for several years at 3000"' (at Armidale in NSW) and often drove considerable distances up to elevations of 5500' in petrol vehicles in the 1970s and 80s (So 1000m to around 1800m in elevation).
Yes altitude and lower air density is a drag.
We were very much performance orientated in those days and often fiddled with carby fuel/air mixture (because we could back then) to compensate when we were heading up into the really high country.
Eventually, I had a pretty good idea how performance would suffer going from sea level to 1800m. I also worked out how to get the most out of the engines as
well. Making them run a bit leaner was all we could realistically do.
Since around 2000 I have travelled the same roads with a friend who drove a modified 4.2 lit Turbo GU Patrol while I drove a reasonably high performance (modified non turbo) 3 Lit Petrol GQ Patrol (with the old high revving but traditionally underpowered Skyline RB30S donk).
The long and short of it was the 4.2 Turbo Patrol did not suffer much at all from the altitude. (It did however have a larger turbo than factory) Whereas my usually gutsy 3 lit petrol went from leaving the Turbo diesel in its dust at sea level to having trouble even keeping at speeds over 90kph up at altitudes over 1400m and certainly suffering at 1800m.
I can affirm the fact that the Turbo Diesel coped far better at altitude than the naturally aspirated petrol engine. I would assume that a naturally aspirated diesel would notice a considerable effect with the lower oxygen levels at altitude.
After my experiences in the 70s and 80s i tried a few experiments with the old Patrol and eventually had some success in the late 2000s
I improved the performance of my Petrol at high altitude by attaching a 60 square inch air
dam to the
snorkel. It seemed to keep the vehicle from running too rich. At speeds of around 110kph I was at least keeping up (or seeming to keep up) with the Turbo Diesel on those high altitude runs. So there seems to be a degree of forced air induction working at those higher speeds.
Obviously the whole reason vehicles are turbo charged is to increase the density of the air and hence O2 flowing into the engine.
It is a known fact that high air temperature even at sea level reduces the density of the air and the amount of available oxygen for any internal combustion engine hence the use of intercoolers and forced air induction and snorkels (to scoop in cooler air from away from the engine bay and warmer road surface) to keep air temperature flowing into the engines cool as possible to improve efficiency and combustion via slightly denser air and hence higher Oxygen levels..
Similarly the effects of altitude can be slightly compensated for by the extra density of air at cooler temperatures.
I can attest to the higher density of cold air and how easy it is to stuff up modern vehicle modifications.
Recently a good friend fried the bores on his cylinders on a very cold night near sea level after he turbo'd his near new diesel engine and had too much fuel flowing into the engine. Obviously in hindsight his fuel levels were above factory settings and the dense cold air (carrying more oxygen which ran the mix hotter than ever) was the straw that broke the camels back so to speak.
His son was driving (no doubt hoofing it) - towing a heavy trailer up a steep long
hill in southern WA in winter - ignoring the pyro gauge which undoubted would have indicated too high a combustion temperature - caused by a combination of denser air (more O2) and plenty of fuel. Needless to say as the bores overheated and became scored - the thing lost compression on the
hill simply conked out - and would not start again! No Compression! The vehicle had performed the same tasks in warmer air temperatures without a problem.
When we pulled the head off - it had scored the tripe out of the cylinders - an expensive lesson.
Hope this
feedback is useful, again I can only speak from personal experience and a reasonable understanding of the physics involved.
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