335d at altitude...

toxicnerve · 08-02-2010, 02:18 PM

Quick question for the panel...

I got back from a euro-roadtrip last week and noticed something. When we were driving through the hill/mountains from Gap to Nice my car started to feel noticably asthmatic.

It felt to me like it was gasping for air and I got the impression I had to rev it quite hard to get any sort of power out of it. Now, I will admit some of the inclines were pretty steep and the car was fairly loaded with myself and the missus (and what seemed like her entire wardrobe) but even so I was surprised at how muted the car felt.

The other thing is, I was expecting it to drink like a mofo with all the constant speeding up and down (with the bends/hairpins in the road)...but it didn't, it barely used any juice at all in those sections! Now my only thought is that if it was struggling to get enough air would it have been fueling less?

Can anyone shed some light on this for me please? Is there something wrong with my car? I have noticed that the red boost hose has some oil on it and the undertray is defo oily so I might get that checked out but I will admit that when on the flat at lower altitudes I could still get the car up to (very) naughty speeds very easily and it pulled like a train all the way...

F31-340i · 08-02-2010, 03:22 PM

Turbocharged cars are usually less affected by altitude than naturally aspirated cars - whilst the air is thinner at high alt, it still has the same ratio of O2, so in effect a turbocharger is capable of cancelling out the effect of altitude by compressing the air - hence why super/turbo chargers used to good effect on spitfire aircraft engines etc.

Whether a car engine management system is able or designed to adjust the boost to compensate for altitude - not sure, but in principle it could. Depends on whether boost pressure is controlled in absolute rather than relative terms by the ECU - I'd be interested to know if it is. In any case the turbo installation is probably optimsed for sea level conditions in a car, hence not running in an optimal way at higher altitudes.

Em135eye · 08-02-2010, 03:27 PM

TBH I'd be very surprised if the mountains in that area are high enough to have much effect.

Unlike the boost hose/oil issue - get that sorted!

briers · 08-02-2010, 03:28 PM

Yes, at altitude the specific volume and air density is less. You would expect to loose around 15-20% power compared to sea level in an N/A car. At about 4-6,000 ft, air density is approximately 85% that of sea level.

On turbo engined cars, normally they have altitude compensation where the ECU detects a lower volume of air coming in through the intake and therefore it fuels accordingly. Maintaining the air/fuel mix ratio.

However, it also detects this reduction in air volume and should compensate by increasing the boost pressure generated by the turbo(s). This is also applicable to hill driving. This is why they suggest to idle for 30-2mins if you've been doing a lot of hill driving. The heat inside the turbo/bearings skyrockets and keeping the oil pumped primed allows the oil to do it's job to dissipate the heat, halving the specific heat in just 1 mile or 2 minutes of off boost driving / idling.

Anyway, you may notice a small performance reduction at lower rpm's, possibly emphasized by 2 passengers and luggage, plus hills. But once the turbo kicks in, especially the second turbo there shouldn't be much difference comparing to sea level.

But, on the fuelling, as mentioned, it shouldn't overfuel when it detects a lack of air or you will get a load of black smoke, unburn't fuel.

If anything, the heat you generated is very positive, keeping max cylinder pressure, efficient injection, soot burn etc.

toxicnerve · 08-02-2010, 03:45 PM

Matt,

3,000m is a fair way up...surely there's a marked difference in air density at that sort of height. Our ears popped a couple of times on the way up and down!

briers, that's good info, cheers.

F31-340i · 08-02-2010, 03:55 PM

3000m is alot in terms of air being thinner - about 10000ft. Snowboarding at that height is certainly very noticable on the lungs!

Spitfires typically had two stage supercharging - with the low speed charger gear optimised around 9000ft, and high speed around 18000ft.

Its potentially easier to manage boost in a turbo with wastegates etc., but I suspect its ability to cope with altitude would be dependant on the size of turbo being able to generate excess boost at given rpm/altitude - this maybe limited if its designed for operation at sea level - plus I suspect a conflicting design aim is to limit turbo lag.

briers · 08-02-2010, 04:03 PM

wow, higher than i thought it's about 2-3% density lost per 1,000 ft and i think there's about 3ft per metre. So thats about 9,000 ft!!

Engine possibly running at or less than 3/4 capacity without the altitude compensation. So i reckon you would have defiantly noticed a sluggishness. Even on the mighty 35d, especially below 3,000 rpm. I believe the second turbo kicks in then so anything above this shouldn't feel any different than sea level. Possibly negligible.

toxicnerve · 08-02-2010, 04:43 PM

We were definitely over 2,575m as the missus took a picture of a mile marker thing that the hill climb cyclists use and we climbed more after that. In fact I am sure I saw one that was in the 2,900m ballpark.

I can't seem to find a topographical/relief map of France to be able to tell you the exact heights to which we climbed sadly...will keep trying.

MPTREE · 08-02-2010, 04:48 PM

this happened on a Top Gear episode once...they went high & had to turn around, cars were spluttering, but so was JC !...don't think it was in France though....anyone see it ?

Em135eye · 08-02-2010, 04:54 PM

toxic - Google Earth it. Run the cursor over the route and it'll give you the altitudes.

Done a bit of mountain running - my ECU appeared not to adapt that well to the altitude and my "fuel" definitely ran a bit lean.

toxicnerve · 08-02-2010, 05:14 PM

Hrm, according to google earth the highest point on my route was around the 2,700m mark, I must have imagined the 2,900 figure that I had in my head...

EDIT:

Thinking about it, on the way back we only went to c.1,000m and I don't recall noticing any drop in performance (evidenced by some pretty swift overtakes of some annoying cars from the Netherlands!) so it was definitely only at the higher altitudes (i.e. 2000m+) that I noticed any issue.

briers · 08-02-2010, 05:17 PM

still 9,000 ft, still high

human error on the mountain side or the fact that google earth height calculations have a margin of error

toxicnerve · 08-02-2010, 05:21 PM

Indeed. I recall thinking that it was bloody high. Also it was noticeably chilly up there with some small patches of snow/ice still on the hillsides.

ss134 · 08-02-2010, 05:22 PM

Hmmmmmm.......upto 20% power loss for N/A at altitude.....note to self - avoid taking on 335d's next time i'm in the French Alps.

toxicnerve · 08-02-2010, 05:26 PM

Quote:

Originally Posted by ss134

Hmmmmmm.......note to self - avoid taking on 335d's next time i'm in the French Alps.

Haha!

It was an epic trip. I really enjoyed it...driving in Europe is such a pleasure compared to the UK. The auto-routes are awesome (no lane hogs), the N and D roads in France are great going too.

I had such a blast and I'd do it again in a heartbeat (and intend to do so)...really loved it.

F31-340i · 08-02-2010, 05:27 PM

...highest road in france is 2800m - which is very very high, higher than the top of the majority of ski resorts.

Highest I've driven is Tioga pass in a convertible Mustang - >3000m in Yosemite, California. Didn't notice much difference though as the 'stang drove like a pretty gutless waterbed at sea level too....

briers · 08-02-2010, 05:29 PM

Quote:

Originally Posted by ///ajd

Didn't notice much difference though as the 'stang drove like a pretty gutless waterbed at sea level too....

haha!

was it a gradual ascent, i.e. over quite a distance ?

ss134 · 08-02-2010, 05:31 PM

Quote:

Originally Posted by toxicnerve

Haha!

It was an epic trip. I really enjoyed it...driving in Europe is such a pleasure compared to the UK. The auto-routes are awesome (no lane hogs), the N and D roads in France are great going too.

I had such a blast and I'd do it again in a heartbeat (and intend to do so)...really loved it.

I agree with you 100% - i'm back in the UK in a couple of weeks time for a couple of months and i'm not looking forward to driving there again TBH.

F31-340i · 08-02-2010, 05:38 PM

Quote:

Originally Posted by briers

haha!

was it a gradual ascent, i.e. over quite a distance ?

Yes, now you mention it I went from west to east - which is a very very gradual climb, into the meadows before the road drops off sharply towards Mono Lake.

Other 'interesting' altitude anecdote was (same holiday) going from the bottom of badwater lake in Death Valley (below sea level - roasting hot) to the mountains to the east 45mins later (much higher - quite chilly!)

m1bjr · 08-02-2010, 05:57 PM

I know the N54 EMU does read absolute pressure to adjust accordingly.
As mentioned although the boost targets are the same, the snails work far harder to get there which affects charge temperatures too.
The abs barometric pressure can be read out from the ECU in realtime

Coolieman1220 · 02-03-2011, 05:05 PM

Quote:

Originally Posted by MPTREE

this happened on a Top Gear episode once...they went high & had to turn around, cars were spluttering, but so was JC !...don't think it was in France though....anyone see it ?

yupp they went through south america. that was a funny episode!

Ti Rich · 02-03-2011, 05:26 PM

Yes Bolivia & Peru I think. Having been to La Paz (highest airport in the world,4061m) it's quite strange coming off the plane and being offered oxygen. There is always 3 people with oxygen standing by the door of the plane in case people collapse!!!

Even stranger driving DOWN though the clouds into the city!

08-02-2010, 02:18 PM	#1
toxicnerve Colonel 96 Rep 2,834 Posts Drives: E92 335d M-Sport Join Date: Jul 2009 Location: UK iTrader: (2)	335d at altitude... Quick question for the panel... I got back from a euro-roadtrip last week and noticed something. When we were driving through the hill/mountains from Gap to Nice my car started to feel noticably asthmatic. It felt to me like it was gasping for air and I got the impression I had to rev it quite hard to get any sort of power out of it. Now, I will admit some of the inclines were pretty steep and the car was fairly loaded with myself and the missus (and what seemed like her entire wardrobe) but even so I was surprised at how muted the car felt. The other thing is, I was expecting it to drink like a mofo with all the constant speeding up and down (with the bends/hairpins in the road)...but it didn't, it barely used any juice at all in those sections! Now my only thought is that if it was struggling to get enough air would it have been fueling less? Can anyone shed some light on this for me please? Is there something wrong with my car? I have noticed that the red boost hose has some oil on it and the undertray is defo oily so I might get that checked out but I will admit that when on the flat at lower altitudes I could still get the car up to (very) naughty speeds very easily and it pulled like a train all the way...
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08-02-2010, 03:22 PM	#2
F31-340i Colonel 160 Rep 2,475 Posts Drives: BMW 340i Touring Join Date: Apr 2007 Location: ... iTrader: (1)	Turbocharged cars are usually less affected by altitude than naturally aspirated cars - whilst the air is thinner at high alt, it still has the same ratio of O2, so in effect a turbocharger is capable of cancelling out the effect of altitude by compressing the air - hence why super/turbo chargers used to good effect on spitfire aircraft engines etc. Whether a car engine management system is able or designed to adjust the boost to compensate for altitude - not sure, but in principle it could. Depends on whether boost pressure is controlled in absolute rather than relative terms by the ECU - I'd be interested to know if it is. In any case the turbo installation is probably optimsed for sea level conditions in a car, hence not running in an optimal way at higher altitudes.
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08-02-2010, 03:27 PM	#3
Em135eye Banned 177 Rep 4,302 Posts Drives: M135i Join Date: Jul 2009 Location: South West iTrader: (0) Garage List 2014 BMW M135i 5 door [0.00]	TBH I'd be very surprised if the mountains in that area are high enough to have much effect. Unlike the boost hose/oil issue - get that sorted!
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08-02-2010, 03:28 PM	#4
briers Ben 62 Rep 1,992 Posts Drives: Tesla p85d Join Date: May 2010 Location: Midlands,UK iTrader: (0)	Yes, at altitude the specific volume and air density is less. You would expect to loose around 15-20% power compared to sea level in an N/A car. At about 4-6,000 ft, air density is approximately 85% that of sea level. On turbo engined cars, normally they have altitude compensation where the ECU detects a lower volume of air coming in through the intake and therefore it fuels accordingly. Maintaining the air/fuel mix ratio. However, it also detects this reduction in air volume and should compensate by increasing the boost pressure generated by the turbo(s). This is also applicable to hill driving. This is why they suggest to idle for 30-2mins if you've been doing a lot of hill driving. The heat inside the turbo/bearings skyrockets and keeping the oil pumped primed allows the oil to do it's job to dissipate the heat, halving the specific heat in just 1 mile or 2 minutes of off boost driving / idling. Anyway, you may notice a small performance reduction at lower rpm's, possibly emphasized by 2 passengers and luggage, plus hills. But once the turbo kicks in, especially the second turbo there shouldn't be much difference comparing to sea level. But, on the fuelling, as mentioned, it shouldn't overfuel when it detects a lack of air or you will get a load of black smoke, unburn't fuel. If anything, the heat you generated is very positive, keeping max cylinder pressure, efficient injection, soot burn etc.
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08-02-2010, 03:45 PM	#5
toxicnerve Colonel 96 Rep 2,834 Posts Drives: E92 335d M-Sport Join Date: Jul 2009 Location: UK iTrader: (2)	Matt, 3,000m is a fair way up...surely there's a marked difference in air density at that sort of height. Our ears popped a couple of times on the way up and down! briers, that's good info, cheers. Last edited by toxicnerve; 08-02-2010 at 05:20 PM..
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08-02-2010, 03:55 PM	#6
F31-340i Colonel 160 Rep 2,475 Posts Drives: BMW 340i Touring Join Date: Apr 2007 Location: ... iTrader: (1)	3000m is alot in terms of air being thinner - about 10000ft. Snowboarding at that height is certainly very noticable on the lungs! Spitfires typically had two stage supercharging - with the low speed charger gear optimised around 9000ft, and high speed around 18000ft. Its potentially easier to manage boost in a turbo with wastegates etc., but I suspect its ability to cope with altitude would be dependant on the size of turbo being able to generate excess boost at given rpm/altitude - this maybe limited if its designed for operation at sea level - plus I suspect a conflicting design aim is to limit turbo lag.
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08-02-2010, 04:03 PM	#7
briers Ben 62 Rep 1,992 Posts Drives: Tesla p85d Join Date: May 2010 Location: Midlands,UK iTrader: (0)	wow, higher than i thought it's about 2-3% density lost per 1,000 ft and i think there's about 3ft per metre. So thats about 9,000 ft!! Engine possibly running at or less than 3/4 capacity without the altitude compensation. So i reckon you would have defiantly noticed a sluggishness. Even on the mighty 35d, especially below 3,000 rpm. I believe the second turbo kicks in then so anything above this shouldn't feel any different than sea level. Possibly negligible. Last edited by briers; 08-02-2010 at 04:10 PM..
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08-02-2010, 04:43 PM	#8
toxicnerve Colonel 96 Rep 2,834 Posts Drives: E92 335d M-Sport Join Date: Jul 2009 Location: UK iTrader: (2)	We were definitely over 2,575m as the missus took a picture of a mile marker thing that the hill climb cyclists use and we climbed more after that. In fact I am sure I saw one that was in the 2,900m ballpark. I can't seem to find a topographical/relief map of France to be able to tell you the exact heights to which we climbed sadly...will keep trying. Last edited by toxicnerve; 08-02-2010 at 05:20 PM..
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08-02-2010, 04:48 PM	#9
MPTREE Private First Class 5 Rep 192 Posts Drives: E92 335i m sport, manual Join Date: Jan 2010 Location: South west iTrader: (0)	this happened on a Top Gear episode once...they went high & had to turn around, cars were spluttering, but so was JC !...don't think it was in France though....anyone see it ?
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08-02-2010, 04:54 PM	#10
Em135eye Banned 177 Rep 4,302 Posts Drives: M135i Join Date: Jul 2009 Location: South West iTrader: (0) Garage List 2014 BMW M135i 5 door [0.00]	toxic - Google Earth it. Run the cursor over the route and it'll give you the altitudes. Done a bit of mountain running - my ECU appeared not to adapt that well to the altitude and my "fuel" definitely ran a bit lean.
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08-02-2010, 05:14 PM	#11
toxicnerve Colonel 96 Rep 2,834 Posts Drives: E92 335d M-Sport Join Date: Jul 2009 Location: UK iTrader: (2)	Hrm, according to google earth the highest point on my route was around the 2,700m mark, I must have imagined the 2,900 figure that I had in my head... EDIT: Thinking about it, on the way back we only went to c.1,000m and I don't recall noticing any drop in performance (evidenced by some pretty swift overtakes of some annoying cars from the Netherlands!) so it was definitely only at the higher altitudes (i.e. 2000m+) that I noticed any issue. Last edited by toxicnerve; 08-02-2010 at 05:19 PM..
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08-02-2010, 05:17 PM	#12
briers Ben 62 Rep 1,992 Posts Drives: Tesla p85d Join Date: May 2010 Location: Midlands,UK iTrader: (0)	still 9,000 ft, still high human error on the mountain side or the fact that google earth height calculations have a margin of error
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08-02-2010, 05:21 PM	#13
toxicnerve Colonel 96 Rep 2,834 Posts Drives: E92 335d M-Sport Join Date: Jul 2009 Location: UK iTrader: (2)	Indeed. I recall thinking that it was bloody high. Also it was noticeably chilly up there with some small patches of snow/ice still on the hillsides.
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08-02-2010, 05:22 PM	#14
ss134 Brigadier General 233 Rep 3,899 Posts Drives: F80 M3 Join Date: Feb 2009 Location: Germany/UK iTrader: (1)	Hmmmmmm.......upto 20% power loss for N/A at altitude.....note to self - avoid taking on 335d's next time i'm in the French Alps. __________________ 2014 AW F80 M3 DCT 2011 AW E90 M3 DCT - Sold 2010 JZB E90 M3 DCT - Sold 2009 6MT E90 LCI 335i M -Sport - Sold
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08-02-2010, 05:27 PM	#16
F31-340i Colonel 160 Rep 2,475 Posts Drives: BMW 340i Touring Join Date: Apr 2007 Location: ... iTrader: (1)	...highest road in france is 2800m - which is very very high, higher than the top of the majority of ski resorts. Highest I've driven is Tioga pass in a convertible Mustang - >3000m in Yosemite, California. Didn't notice much difference though as the 'stang drove like a pretty gutless waterbed at sea level too....
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08-02-2010, 05:57 PM	#20
m1bjr LSD - No, you're not seeing things 72 Rep 3,302 Posts Drives: Baby F36 Gran Coupe Join Date: Mar 2010 Location: Plymouth UK iTrader: (4)	I know the N54 EMU does read absolute pressure to adjust accordingly. As mentioned although the boost targets are the same, the snails work far harder to get there which affects charge temperatures too. The abs barometric pressure can be read out from the ECU in realtime
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02-03-2011, 05:26 PM	#22
Ti Rich Major 303 Rep 1,315 Posts Drives: Porsche Macan S D Join Date: Jan 2008 Location: Dudley, West Midlands, UK iTrader: (0)	Yes Bolivia & Peru I think. Having been to La Paz (highest airport in the world,4061m) it's quite strange coming off the plane and being offered oxygen. There is always 3 people with oxygen standing by the door of the plane in case people collapse!!! Even stranger driving DOWN though the clouds into the city!
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