The Mother of all 335i vs IS350 threads (please read 1st post in thread!)
07-22-07, 11:46 AM
#826
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No you are not correct. To get 10psi of manifold boost at altitude is no harder than at sea level. The only difference is that you are starting with 12.2 atmospheric pressure instead of 14.7 at sea level. So with 10psi of boost you would have 22.2 absolute boost pressure at altitude instead of 24.7 absolute presure at sea level. Which mean you are only losing 8% of your power versus about 17% for a normally aspirated engine. Stock turbos have enough extra capacity in them. You can read more here: http://www.eurotuner.com/featuredveh...mw_335i_coupe/ It states the following "So what's under the 335i's hood? "We have two Mitsubishi turbos running at 0.6bar (8.8psi). These can boost to 0.8bar to compensate for altitude using the two electronically-controlled wastegates," Udo explained."
07-22-07, 12:15 PM
#827
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No, I am not correct? Really? How do you arrive at this conclusion? I showed you it takes 8% more effort to make 10 psi boost at altitude. Do you know how to read a compressor map? If you do, it should be obvious, and we would not be having this discussion. If you don't raise the boost, you lose power almost identically to your NA counterpart. If you raise boost by adding heat and not increasing mass-flow, you still lose, because it all comes down to mass-flow, not PSI.
07-22-07, 12:25 PM
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Dude, you obviosly don't know much about turbos and altitude. Here is another link for you to study: http://www.turbos.bwauto.com/product...dvantages.aspx "The high-altitude performance of a turbocharged engine is significantly better. Because of the lower air pressure at high altitudes, the power loss of a naturally aspirated engine is considerable. In contrast, the performance of the turbine improves at altitude as a result of the greater pressure difference between the virtually constant pressure upstream of the turbine and the lower ambient pressure at outlet. The lower air density at the compressor inlet is largely equalized. Hence, the engine has barely any power loss. "
I could be incorrect though.
Cheers,
Old Oiler
07-22-07, 12:36 PM
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07-22-07, 12:41 PM
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No, I am not correct? Really? How do you arrive at this conclusion? I showed you it takes 8% more effort to make 10 psi boost at altitude. Do you know how to read a compressor map? If you do, it should be obvious, and we would not be having this discussion. If you don't raise the boost, you lose power almost identically to your NA counterpart. If you raise boost by adding heat and not increasing mass-flow, you still lose, because it all comes down to mass-flow, not PSI.
So, I would assume that most turbos do indeed spin faster producing more boost at higher altitude out of necessity. This would seem to be less efficient and slower, creating more lag, but still producing higher peaks in power than its NA couterpart relative to their sea-level-going siblings.
07-22-07, 12:42 PM
#831
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Dude, you obviosly don't know much about turbos and altitude. Here is another link for you to study: http://www.turbos.bwauto.com/product...dvantages.aspx "The high-altitude performance of a turbocharged engine is significantly better. Because of the lower air pressure at high altitudes, the power loss of a naturally aspirated engine is considerable. In contrast, the performance of the turbine improves at altitude as a result of the greater pressure difference between the virtually constant pressure upstream of the turbine and the lower ambient pressure at outlet. The lower air density at the compressor inlet is largely equalized. Hence, the engine has barely any power loss. "
07-22-07, 01:05 PM
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Ive always thought as well that turbos are more efficient at altitude than N/A motors. I dont have any fancy formulas to prove it but...Although the cars are apples and oranges, i lived at sea level and in CO. My 86 corvette felt like it changed SIGNIFICANTLY more than my 03 WRX at altitude. Meaning the loss of the vette's power was a lot more noticable than the loss of the wrx (turbo) power driving from SL up to 7k feet in CO. Also driving from 7kfeet on the front range up to 10k in the moutains yielded another signifcant loss in the vette, the wrx did not seem to change as much.
07-22-07, 01:33 PM
#833
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TESTOSTERONE 4EVA!!!
07-22-07, 01:37 PM
#834
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Dude, you obviosly don't know much about turbos and altitude. Here is another link for you to study: http://www.turbos.bwauto.com/product...dvantages.aspx "The high-altitude performance of a turbocharged engine is significantly better. Because of the lower air pressure at high altitudes, the power loss of a naturally aspirated engine is considerable. In contrast, the performance of the turbine improves at altitude as a result of the greater pressure difference between the virtually constant pressure upstream of the turbine and the lower ambient pressure at outlet. The lower air density at the compressor inlet is largely equalized. Hence, the engine has barely any power loss. "
Click here for more of this subject that I understand perfectly well. Now, please point out my deficiency.
# That’s great, but what if you’re not at sea level? In this case, simply substitute the actual atmospheric pressure in place of the 14.7 psi in the equations above to give a more accurate calculation. At higher elevations, this can have a significant effect on pressure ratio.
For example, at Denver’s 5000 feet elevation, the atmospheric pressure is typically around 12.4 psia. In this case, the pressure ratio calculation, taking into account the intake depression, is:
(12 psig + 12.4 psia) / (12.4 psia – 1 psig) = 2.14
Compared to the 1.82 pressure ratio calculated originally, this is a big difference.
# As you can see in the above examples, pressure ratio depends on a lot more than just boost.
For example, at Denver’s 5000 feet elevation, the atmospheric pressure is typically around 12.4 psia. In this case, the pressure ratio calculation, taking into account the intake depression, is:
(12 psig + 12.4 psia) / (12.4 psia – 1 psig) = 2.14
Compared to the 1.82 pressure ratio calculated originally, this is a big difference.
# As you can see in the above examples, pressure ratio depends on a lot more than just boost.
Do you understand the concept of efficiency islands? Do you understand mass-flow and pressure ratio? If you don't then I can see why you would come to a misguided conclusion.
AFA aircraft - absolutely they use turbos to extend operating altitude. But again, it's through careful turbo selection for a range of altitude. It's not just slap on a turbo and everything works better.
07-22-07, 01:42 PM
#835
Colder air is usually in areas of altitude. The cold air helps both cars but AFAIK/IMHO the turbo cars will generally see more of a performance increase. Just thought I'd throw that in.
07-23-07, 01:41 PM
#836
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i testdrove a brand new 335i and have a fully broken-in is350. yes, the 335i is still faster, to me, it's a lot faster! no doubt! but i am glad that i have the is350. i haven't had a single problem with my car, but my mom's fully loaded 07 328i couple has already returned back to dealer 2 times since jan 07. one was for the abs sensor and the other was for the tire pressure sensor and seat belt assistance. plus, bmw didn't even provide any loaner to her and my mom needed to ask someone to pick her up...omg...i couldn't believe a lexus competitor didn't provide loaner service!!
08-11-07, 08:48 PM
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335i with the paddle shifters , keyless fob , navi , leather seating , automatic trans will cost you msrp of 49k .....and in the most blatant of truths .. .the navi and idrive on the 335i is not nearly as good as the lexus navi ... for one the resolution on the 335i isnt up to par with the IS350's ...the functional aspects of the idrive system is also not as numerous as the lexus nav unit ... plus I also found the is350's interior to be much better for the 335i's ... the seats are more comfortable in the lexus and the overall setup in the lexus feels very comfortable as compared to the 335i in which I felt the seats were stiff ... the overall interior didnt really impress me enough to want to pay nearly 50k ... The 335i does have " some " nice features , such as the hands free phone which I feel is one of the few things it is better then the is350 in .. and the cup holders actually caught my interest with its climate controlled feature ... overall I dont really find the 335i sedan to be all that appealing , but the 335i coupe is a beautiful mean sounding car ... the lexus overall in comparable categories gets the win ... unless your all about handling .. and if money is no issue buy a m5 lol :P
08-11-07, 09:07 PM
#838
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Maybe IS350 vs I35i Coupe
Just to complicate matters, another candidate for consideration is the new BMW I35i coupe. See "Upfront" article in Sept. 07 Car & Driver. Same motor as the 335i, but less weight and less price...~$33,000! Performance expected to exceed that of the 335i. Decisions, decisions...ain't competition great!
