I know DA affects all the cars out there but does elevation alone affect turbo cars? I heard it from somewhere that just elevation alone does not affect turbo cars but it plays a huge role in NA or even supercharged cars?
Can anyone confirm this?

I have done some experiments with my friends 2007 GTI and the results are different when we race 1200ft above see level. I don't pull on him as hard as I do in where i love which is close to see level.

FYI he lives near california speedway (local dragstrip).

 

Yes, turbo cars aren't remotely as affected by DA as an NA car. The reason is the turbo car generates it's own atmosphere and newer turbo cars (early 1990s and above) have the ability increase boost to compensate for the thinner air. This is why having a turbo car when living at higher elevations is key. If I lived at an elevation above 2000', I'd have a turbo car. The SC car can't really compensate for the worse DA because the SC can't vary it's boost.

Additionally, many turbo cars are not significantly impacted by ambient temp because the air being ingested into the motor is already screaming hot. An additional increase in temp of 20 to 40 degrees isn't going to make a huge difference. Don't misunderstand me, though, because turbo cars can tend to heat soak quickly and will loose power, but that's different than just an increase in ambient temp. I have a couple friends with a modded WRXs/STIs and those cars are hardly impacted by DA. They run within .2 seconds regardless if it's 40 degrees and dry or 90 and muggy.

 

^thanks for clarifying dave. Running with 335s at the dragstrip and where i live, we get different results. I lose by a car at the drag strip but we can see each other's faces no matter how fast we go, here where I live. At the same time when I run against NA cars like the newer G35/g37s the results are the same no matter where we are at.

 

I beg to differ.... A turbo will still be affected with Ambient Temp since it is still injecting air from the outside. The turbo is just basically compressing air that it gets from the outside so there is a difference between compressing a 30F denser air compare to a 90F less denser air. The SC wouldn't be able to adapt to air density since the boost is dictated by your RPM while turbo use the wastegate to achieve the proper boost. Ask anyone who has a turbo and they will tell you that their car all perform better or will feel much powerful on colder days compared to hot humid day. I'm from NYC so I do experience a wide change in temp and trust me I feel the difference. My Gtech even show me the difference with my TQ/WHP on my Winter Pulls and my early Summer pulls. I lost at least 10-20whp (Gtech uses Net HP by the way) when the ambient temp was around 85F compared to my pull when the Ambient temp was 40F. Also without touching my Boost Map, I usually hit 8.0 - 8.3psi on colder days (30F-50F) and now in the summer days I'm only hitting 7.5-7.8psi on hotter days (80F +). If I have an Electronic Boos Controller then it won't be a problem since the EBC will make adjustment to get to that target boost, the problem is I don't have an EBC so I have to manually change my BCS duty cycle.

 

My friends with WRXs and EVOs would beg to differ. Maybe the problem lies with the fact that your car wasn't designed for boost and theirs were. I'm talking about all the ECU controls and variability which your G doesn't have.

Regardless, the overall point is turbo cars aren't remotely as affected by density altitude as a naturally aspirated car. On a day with a 5,300' DA, an NA car will be loosing about 15% of it's power whereas the turbo car might only be loosing 5%, if that.

 

What's DA? Dry Air?

 

Density Altitude.

http://www.google.com/search?hl=en&safe=off&rlz=1G1GGLQ_ENUS282&q=define%3Adensity+altitude&btnG=Search

 

Thanks. Never heard of it referred to as "DA" before. . .especially in pilot land. (Sorry. . .too many acronyms with subscripts.) When I googled it, I got back "deviant art" and when I wiki'd I got "district attorney".
That being clarified, "DA" is variable with heat, humidity, and barometric pressure. It can be used to correlate to an equivalent ASL (above sea level) altitude at standard temp, press, etc. Therefore, you could theoretically have a REALLY hot and muggy day at sea level and have your engine performance worse than if it is REALLY cold and dry at 2000 feet ASL. But, that's only for NA engines. With a turbo airplane engine, the turbos are there merely to keep the manifold pressure the same whether you're at sea level or at 30,000 feet (turbo-normalized). Anyway, I guess I'm curious, what the OP was really trying to get at, since it seems to me he's basically asking if "altitude" or "altitude corrected for temp/press/humidity" have an affect on turbo engines? I guess my answer would be that "DA" has the same affect on a turbo engine as being at the same equivalent altitude ASL. . .but it also depends on how the wastegate is set up: normalized to maintain a constant pressure, or just a %increase over ambient pressure (ignoring effects of temperature and humidity). I think with a lot of the newer fancy piggybacks, you can do stuff like that?

On a side note, when my dad moved from CT (~sea level) to Colorado (~5280 feet) he had to change the pulley on his supercharger since, as someone stated, the boost is just %increase over ambient based on RPM. He was seeing ~7psi in CT and 4.5-5.5 in Colorado (pre pulley change and tune).

 

^My question was about turbo cars. From what i understand, modern car's ECU adjusts the boost to the outside temp/humidity/elevation to keep the power to whatever the target hp is for a particular car therefor the car is not affected by those factors like the NA car would. Dave's explanation makes perfect sense.

 

Car and Driver has a segment titled Frank Kafka's Garage, on the last page of every issue. The June 08 issue("24 cars worth waiting for") discusses this very topic. I tried to find a link to the page online, but came up with nothing.

It basically states everything Dave has already said. Fortunately I have the copy on my desk. Here's a direct quote:

 

Understood. Altho, piston engines are piston engines. In fact, Mooney used to make a plane that had a porsche flat 6 engine straight out of a 911. I guess I was trying to reiterate what daveb said. I should have stated it more clearly: NA affected by any form of altitude change (be it true altitude, density altitude, etc). Turbo (car/plane whatever) not affected/minimally affected, with the caveat that it also depends how the turbo is controlled via the ECU.

Edit: What trey just posted.

 

thanks everyone for a clear explanation to this question.