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      06-23-2012, 04:39 PM   #13
Gearhead999s
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Drives: E93 335is(wifes)E92 M3
Join Date: Apr 2007
Location: Toronto

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Quote:
Originally Posted by 767IJP View Post
I am aware of what density altitude is. I'm just saying this will have zero to do with this guys problem. The guy is located in Toronto. I doubt even a 150 degree day would cause a reduction in power worthy of making his car drive so noticeably that it's "crap".

Turbo chargers, at least in piston powered aircraft increase manifold pressure to counteract increases in pressure altitude to make the engine keep sea level manifold pressure to altitudes where significant power losses would occur. I would say they'd do the same in cars so I can't see a turbo powered car performing worse than a NA car when it comes to density altitude.

I would also imagine the fuel injection system on this car is advanced enough to optimize fuel patterns when in comes to altitude/temp. I would say the density altitude argument is pretty moot. Toronto being at 570 feet A 100F day would have a density alt of about Calgary on a standard ISA day- 29.92/15C. We aren't hearing many compliantly from there.
When you dyno a engine in order to know the true horsepower it is developing you must do a correction factor based on temperature and pressure altitude.I have had lots of turbo cars over the years and they all fell off big time in the heat and had lots more turbo lag in normal driving.My wifes 335is is also very much like this and makes really dislike the idea of the next M3 being F!.
A good practical example of supercharged powerplants suffering in the heat was at Mosport 2 weeks ago with the Mustang guys.My M3 with maybe 350-RWHP has no problem pulling 500+RWHP Stangs up the straight on a 35c day.These guys were all complaining about how much down on power their cars felt compared to the cooler AM.Some engine management systems probably loose more power than others in these conditions but I have noticed this in everything that I have owned over the years.

By the way I have over 5700 hrs TT with 5300 M/E.I used to spend a lot of time over FL20 in piston aircraft working photo survey so I am pretty familar with the effect of temperature & altitude on performance of piston engines & airframes.
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