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XBimmers | BMW X3 Forum BMW X3 and X4 Forums | F25 (2011 - 2017) | F26 (2014 - Current) Second Generation BMW X3 General Forum Turbo performance at altitude

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      01-18-2012, 10:12 AM   #1
cadman50
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Turbo performance at altitude

Never having owned a turbo before, but will be shortly, how does driving in the mountains affect the overall performance of the 35i engine? I'm not so much concerned around northern NE but more so in the western mountains going from elevations of, say, 4000ft up to 8000-9000 feet? Either at highway speeds or slow crawls up winding canyon roads.
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      01-18-2012, 10:18 AM   #2
bren
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You will find the turbo to be advantageous over a naturally aspirated car at altitude.
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      01-18-2012, 10:37 AM   #3
jsublime
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Check wikipedia tomorrow.

Although the air is thinner and easier to compress, the turbo will likely lose some power, but not nearly as much as a NA engine would. This is why you see lots of turbo engines for events such as pikes peak hill climb.
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      01-18-2012, 04:13 PM   #4
n55x3
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IMHO if you live anywhere above 5000' a turbo car is the only way to go. I've driven over Eisenhower Pass (11,150') on numerous occasions and the difference between a N/A car and a turbo is night and day. I've been in 300+ hp n/a cars that required multiple downshifts to maintain speed. While I've gone over the pass in ~200 hp turbo motors that purred right up the mountain all while keeping the RPMs decently low.

I haven't driven the X3 over the pass yet but we did take it up the Mt. Washington auto road in NH and it was never at a lack of power. It pulled nicely at low rpms (this ZF 8 spd in normal mode HATES to downshift).
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      01-18-2012, 05:00 PM   #5
cadman50
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Quote:
Originally Posted by n55x3 View Post
IMHO if you live anywhere above 5000' a turbo car is the only way to go. I've driven over Eisenhower Pass (11,150') on numerous occasions and the difference between a N/A car and a turbo is night and day. I've been in 300+ hp n/a cars that required multiple downshifts to maintain speed. While I've gone over the pass in ~200 hp turbo motors that purred right up the mountain all while keeping the RPMs decently low.

I haven't driven the X3 over the pass yet but we did take it up the Mt. Washington auto road in NH and it was never at a lack of power. It pulled nicely at low rpms (this ZF 8 spd in normal mode HATES to downshift).
I think that Mt. Washington auto road in NH is pretty steep in some places as I've heard. I'll be driving some fairly steep canyon roads thruout the west at slow speeds and wondered if I would be losing power and have to constantly downshift or not. Seems like I have an answer now. Thanks alot.
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      01-18-2012, 05:26 PM   #6
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Yeah I think you'll be fine, you'll have more than enough power. The auto road did have some really steep places and while going up we mostly bounced between 2nd and 3rd gear always cruising around 10 mph.

With the tranny in sport mode it does a really good job of holding gears and it is still easy to manually drop down another gear and keep it there as needed. Also, unlike other manu-matics, when you manually select 3rd gear, for example, you can floor it and it will never up shift or down shift, it stays locked in that gear which is really nice and comparable to a normal manual.
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      01-18-2012, 06:53 PM   #7
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I'm guessing there would be some minimal loss. I've heard for NA it's about a 3% loss for every 1000 feet in elevation and for a turbo it's more like 1% for every 1000 ft. Maybe someone else can confirm what the actual loss would be on the N55. I'm in Colorado Springs around 6000ft so I've been wondering this myself.
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      01-18-2012, 08:41 PM   #8
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Quote:
Originally Posted by n55x3 View Post
IMHO if you live anywhere above 5000' a turbo car is the only way to go. I've driven over Eisenhower Pass (11,150') on numerous occasions and the difference between a N/A car and a turbo is night and day. I've been in 300+ hp n/a cars that required multiple downshifts to maintain speed. While I've gone over the pass in ~200 hp turbo motors that purred right up the mountain all while keeping the RPMs decently low.

I haven't driven the X3 over the pass yet but we did take it up the Mt. Washington auto road in NH and it was never at a lack of power. It pulled nicely at low rpms (this ZF 8 spd in normal mode HATES to downshift).
Last fall I drove I-70 from Utah to Kansas over the aforementioned Eisenhower Pass with the outside air temp a warm 70-80 F making the Density Altitude considerably higher than 11,150 ft and I could discern no significant difference in the power and performance of the engine. It felt the same as it does @ sea
level where I live. I know my evaluation is subjective but the way the car blew through the Rockies passing everything effortlessly enforces my belief that nearly full power was available.
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      01-19-2012, 02:33 AM   #9
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I have made several trips over the mountain passes, aforementioned Eisenhower as well as Vail and Monarch passes and enjoyed every minute of the drive. The X3 35i easily passed when ever I wanted to and in fact will run as fast as you feel safe driving. (Within the speed limits of coarse)

Lotus7, thank you for the technical explanation. I like ColoradoX3 have been curious about the technical affect of altitude on the N55 turbo engine. That said, my seat of the pants experience tells me there is little if any impact by the altitude on this engine.
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