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      12-03-2007, 11:54 AM   #1
john970
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Altitude effect on 135i turbos

I was considering an 07 EVO before I decided to wait for the 1er and discovered that in that car the turbo makes up about 1/2 the difference in altitude (i.e. cylinder air pressure difference at 5000 feet is halved compared to a naturally aspirated car).

Does anyone know how the 1er computer handles altitude difference? I've heard people guess that it makes up the complete difference, but this would increase lag quite a bit. The turbos would have to spool up quite a bit faster to make up the pressure difference, and this seems counter to BMW's intention for the engine.

I have an '02 A4 1.8T auto and it is a dog when I go up into the mountains (8,000+). The shift points go way up, and even after the turbo spins up the car is generating way less power than it does even in Denver at 5200 feet.

This question is also important in determining whether it makes sense to mix 100 octane in with the 91 I get at the pump - if there isn't enough air in the cylinder at altitude it wouldn't matter.
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      12-03-2007, 05:09 PM   #2
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Quote:
Originally Posted by john970 View Post
I was considering an 07 EVO before I decided to wait for the 1er and discovered that in that car the turbo makes up about 1/2 the difference in altitude (i.e. cylinder air pressure difference at 5000 feet is halved compared to a naturally aspirated car).

Does anyone know how the 1er computer handles altitude difference? I've heard people guess that it makes up the complete difference, but this would increase lag quite a bit. The turbos would have to spool up quite a bit faster to make up the pressure difference, and this seems counter to BMW's intention for the engine.

I have an '02 A4 1.8T auto and it is a dog when I go up into the mountains (8,000+). The shift points go way up, and even after the turbo spins up the car is generating way less power than it does even in Denver at 5200 feet.

This question is also important in determining whether it makes sense to mix 100 octane in with the 91 I get at the pump - if there isn't enough air in the cylinder at altitude it wouldn't matter.
I dynoed 280whp stock at 4200 feet if that helps(mustang dyno). I heard tuners say that there is no power loss up until around 5k feet. Stock max boost is 8.5 at sea level, the ecu can compensate up to 10.5 psi. I guess you could do the math to see when the extra 2 psi couldn't make up the diff in altitude, I don't know how to do that.

My buddy dynoed 272 whp in boulder, CO which is still as much as many others have dynoed at sea level. You can always buy a piggyback for 400-1500 that will up boost to 11-14 psi to make up the diff as well.
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      12-03-2007, 07:27 PM   #3
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Quote:
Originally Posted by 335ito135i View Post
I dynoed 280whp stock at 4200 feet if that helps(mustang dyno). I heard tuners say that there is no power loss up until around 5k feet. Stock max boost is 8.5 at sea level, the ecu can compensate up to 10.5 psi. I guess you could do the math to see when the extra 2 psi couldn't make up the diff in altitude, I don't know how to do that.

My buddy dynoed 272 whp in boulder, CO which is still as much as many others have dynoed at sea level. You can always buy a piggyback for 400-1500 that will up boost to 11-14 psi to make up the diff as well.
Correct me if I'm wrong here, but I thought dynos take altitude, temperature, and humidity into consideration and correct it so you can compare apples to apples.

Not sure I would want to "make up the difference" as you don't get anything for free. More boost = higher turbine rpm = more lag, no matter the altitude. What the question here is is what the stock 135i ECU behavior is. All I was able to learn so far is that it does take altitude into effect in determining the waste gate position, but I don't know how.
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      12-03-2007, 07:33 PM   #4
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John - if you aren't already aware of them, you may want to wander over to the e90 boards and see what they have to say about on the N54 at altitude.
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      12-04-2007, 11:00 AM   #5
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Quote:
Originally Posted by atr_hugo View Post
John - if you aren't already aware of them, you may want to wander over to the e90 boards and see what they have to say about on the N54 at altitude.
Did a few searches and came up empty. If I find anything out I'll post.
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      12-04-2007, 11:50 AM   #6
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Quote:
Originally Posted by john970 View Post
I have an '02 A4 1.8T auto and it is a dog when I go up into the mountains (8,000+). The shift points go way up, and even after the turbo spins up the car is generating way less power than it does even in Denver at 5200 feet.

This question is also important in determining whether it makes sense to mix 100 octane in with the 91 I get at the pump - if there isn't enough air in the cylinder at altitude it wouldn't matter.
My experience with my car is completely different than yours. I feel almost no difference at all going above 8000+ altitude compared to Denver.

I don't know if it is my manual transmission, or that I mix 105 octane fuel into my tank with every fill-up. But whatever it is, I'm very, very happy with how well it performs at high altitude. I am expecting a manual tranny 135i turbo with an engine tune and 105 octane fuel mixed in will perform even better, but I have no proof. It's just my gut feeling.

When I drive non-turbo vehicle up the same Interstates/highways, I feel like somebody stole my I-6 and replaced it with a 4-cyl. My turbo car just doesn't feel that way at all. In fact, if it is a 100+ degree day, and I take my turbo car to higher altitude and it is in the 70's up there, my car actually performs better at altitude with the temp. change than it did down in town. I have the speeding tickets to prove it. :frown:

Last edited by Nixon; 08-10-2009 at 04:04 PM..
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      12-04-2007, 01:45 PM   #7
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Quote:
Originally Posted by Nixon View Post
My experience with my '01 A4 1.8T manual w/APR chip is completely different than yours. I feel almost no difference at all going above 8000+ altitude compared to Denver.

I don't know if it is my manual transmission, the lighter, older body style of the 2001, the APR chip, or that I mix 105 octane fuel into my tank with every fill-up. But whatever it is, I'm very, very happy with how well it performs at high altitude. I am expecting a manual tranny 135i turbo with an engine tune and 105 octane fuel mixed in will perform even better, but I have no proof. It's just my gut feeling.

When I drive my Jeep Wrangler up the same Interstates/highways, I feel like somebody stole my I-6 and replaced it with a 4-cyl. My turbo A4 just doesn't feel that way at all. In fact, if it is a 100+ degree day in Denver, and I take the A4 to higher altitude and it is in the 70's up there, my car actually performs better at altitude with the temp. change than it did down in Denver. I have the speeding tickets from a few miles above Georgetown to prove it. :frown:
As a pilot I can tell you that temperature has a small effect on pressure relative to the huge effect a change in altitude has. On any given day the pressure at a given altitude can vary, but this has more to do with weather fronts than temperature changes. Here is a calculator you can play with yourself:

http://wahiduddin.net/calc/calc_da.htm

Maybe your chip automatically spools the turbo up to max boost which would compensate more for the altitude, but there is no way you are getting more power with less air pressure. I can tell you my stock 1.8T doesn't behave that way, although I am sure it does better than a naturally aspirated car.

In the older turboed planes that I fly, I can overboost the engine simply by shoving the throttle all the way forward at sea level. Proper operation is boosting to a specific manifold pressure on takeoff, and as you climb the manifold pressure drops and you increase the throttle (and boost) to maintain the same power level (up to a point, usually 10k-12k feet). However, in an airplane lag is not an issue (no stoplights).

Where do you get 105 octane in Denver??? I would like to try a tank.
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      12-04-2007, 03:22 PM   #8
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I think the complexity of the ping sensor/chip programming/intercooler efficiency at different ambient temps/etc... has more effect on my actual performance than the theoretical factors that you correctly listed.

Having a clutch together with a chip greatly reduces the negative effect of lag on my driving experience. The chip brings the hp/torque curve way down to lower RPM's, and I can use the clutch to keep the RPM's higher than an auto during aggressive acceleration from a stop.

You can't fill your tank with the 105 octane fuel I buy. It is only good for using as an octane booster. At the risk of starting an anti-Ethanol flame war, I'll let you in on my secret. I mix in enough E-85 at $2.09/gallon to make about an E-20 mix. E-85 is available in about a dozen places around my area.

You can add a few gallons of E-85 to your tank of 91 octane without having much effect on the AFR. Your car is already designed to run at an AFR of 13.6:1, and E20 has an AFR of about 13:1. But this gives you an octane rating of about 94. My car seems to adjust very well to both the AFR change, and the added octane. The power boost is obvious even to my wife, and I ran about an E-30 mix for my latest emissions test, and emissions were much better than just straight 91 octane.

DISCLAIMER (not aimed at you in particular, john970): A mix of 91 octane and E-85 that is equal to about E-20 works very, very well with my car, with my chip installed. Other's results may differ. And like any performance mod, there could be some chance (no matter how small) that a car might not like E-20. Hopefully this disclaimer will keep the flames away. But I'm putting on my flame-proof underwear anyways. I will not respond to anybody who claims that E-20 will make your car explode due to the increased electrical conductivity of pure E-100 Ethanol.

Last edited by Nixon; 08-10-2009 at 03:21 PM..
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      12-05-2007, 11:21 AM   #9
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Quote:
Originally Posted by john970 View Post
Correct me if I'm wrong here, but I thought dynos take altitude, temperature, and humidity into consideration and correct it so you can compare apples to apples.

Not sure I would want to "make up the difference" as you don't get anything for free. More boost = higher turbine rpm = more lag, no matter the altitude. What the question here is is what the stock 135i ECU behavior is. All I was able to learn so far is that it does take altitude into effect in determining the waste gate position, but I don't know how.

There are user programmable tunes so you can have the boost increased slowly over stock as the rpm's climb so the lag isn't noticable. Mine is 10psi at 3k, 11@4k, 11.5@4.5, 12@5, 13@5.5, 14@6k, etc.
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      12-05-2007, 02:46 PM   #10
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Ask the Denver 335i owners at e90post.com

If your a pilot, just splurge the $795 for a piggy-back ecu from Attache. Less expensive than the PROCEED (by almost 50%) with more HP, its made its way to the top of my mod list. Of course I dont think its totally out yet and $795 is the target price, so it could be more..........or less...

I know I dont make pilot money, but I'm sure I also dont have pilot bills...

Here is a link, maybe you could ask them if their tune could help you out...

http://www.e90post.com/forums/showthread.php?t=96227

Good luck!
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      02-06-2008, 05:54 PM   #11
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Anyone have any new info on this?
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      02-06-2008, 10:28 PM   #12
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It probably has an altimeter as one of the sensors feeding into the ecu. The only turbo engine I have intimate familiarity with is the fabulous old Audi I-5 20v 2.2 turbo. It had an altimeter as one of almost 40 different ecu sensors. Sorry to contribute conjecture rather than fact specific to the 135 engine, but rest assured that high altitude performance has always been a forte of turbo engines, and was a big factor in Audi's period of Pike's Peak dominance.
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