my theory on lag... am I close? (for the confused newbie)
10-09-2002, 08:53 AM
#12
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Even more basic stuff... PV= nRT
The Ideal Gas Law
n = number of molecules
P = pressure
V = volume
R = gas constant
T = temperature
1 = initial values
2 = final values
n2/n1 = (P2V2)(RT1)/(P1V1)(RT2)
n2/n1 = (P2V2T1)/(P1V1T2)
if PV = constant =>
n2/n1 = T1/T2
So, for an ideal gas, which is allowed to expand/contract as it's heated/cooled (maintaining a constant PV), the change in the number of molecules of the gas found within a given space is inversely proportional to the change in temperature. Hotter = less dense, Cooler = more dense.
n = number of molecules
P = pressure
V = volume
R = gas constant
T = temperature
1 = initial values
2 = final values
n2/n1 = (P2V2)(RT1)/(P1V1)(RT2)
n2/n1 = (P2V2T1)/(P1V1T2)
if PV = constant =>
n2/n1 = T1/T2
So, for an ideal gas, which is allowed to expand/contract as it's heated/cooled (maintaining a constant PV), the change in the number of molecules of the gas found within a given space is inversely proportional to the change in temperature. Hotter = less dense, Cooler = more dense.
10-09-2002, 09:27 AM
#13
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But he's comparing heat & elevation only...
...and notices more lag than at sea level in cool conditions.
Surely you're not suggesting that heat & elevation somehow change the bahavior of the transmission? HPH
Surely you're not suggesting that heat & elevation somehow change the bahavior of the transmission? HPH
10-09-2002, 11:01 AM
#14
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Hey, that's what I said....but I knew someone would bring up pv=nRT :-)
I knew high school chemistry and physics would come in handy!
But here's a question. One of the reasons I got the turbo was because people claim they are not affected by altitude as much as a normally aspirated engine. Does this mean that with a lower density of air, the turbos are working harder? And if so, what effect would a chip have at high altitude? I'd think with a lower density air, the turbos would be working extra hard?
But here's a question. One of the reasons I got the turbo was because people claim they are not affected by altitude as much as a normally aspirated engine. Does this mean that with a lower density of air, the turbos are working harder? And if so, what effect would a chip have at high altitude? I'd think with a lower density air, the turbos would be working extra hard?
10-09-2002, 11:19 AM
#15
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Turbos still try to maintain intake pressure, at high altitude...
But the impeller will be spinning at a much higher frequency to do so. This in turn will heat the air somewhat, raising it's pressure a little bit. If you're at high altitude during ski season, I expect it won't be much of an issue. If it's too hot at high altitude, or you're just too high period, even turbos become innefective at preventing power loss.
W/o considering different temps for different locations & seasons, some approximations I've seen are as follows.
- N.A. engine power loss with altitude ~ 3% per 1000ft.
- Turbo engine loss with altitude ~ .5% per 1000ft.
(A lot more about this exists on Piloting web discussions, as Pilot's have to factor in their power loss when calculating how high/fast they can climb.)
W/o considering different temps for different locations & seasons, some approximations I've seen are as follows.
- N.A. engine power loss with altitude ~ 3% per 1000ft.
- Turbo engine loss with altitude ~ .5% per 1000ft.
(A lot more about this exists on Piloting web discussions, as Pilot's have to factor in their power loss when calculating how high/fast they can climb.)
10-09-2002, 12:45 PM
#16
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I don't know about the turbo losses, but...
...your NA figure of 3% per 1000' scales well to density -- in that figure of mine (in the "Engineers..." post above), 900 mb ~ 1000 m ~ 3300' and 800 mb ~ 2100m ~ 7000'.
And a 20% or so power loss here in Santa Fe is probably about right. It puts the 300HP 4.2 V8 down to 240HP or so -- right about where the 2.7T is with your .5% figure. (And it put my A4's 190HP 2.8 V6 down to around 150HP -- yuck).
But, if your turbo number is right, then an RS6 would still be up around 435HP -- yee haw. HPH
And a 20% or so power loss here in Santa Fe is probably about right. It puts the 300HP 4.2 V8 down to 240HP or so -- right about where the 2.7T is with your .5% figure. (And it put my A4's 190HP 2.8 V6 down to around 150HP -- yuck).
But, if your turbo number is right, then an RS6 would still be up around 435HP -- yee haw. HPH
10-09-2002, 03:04 PM
#17
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The hard life of a turbo - Interesting A6 forum thread.
<ul><li><a href="https://forums.audiworld.com/a6/msgs/194458.phtml">https://forums.audiworld.com/a6/msgs/194458.phtml</a</li></ul>
10-09-2002, 03:37 PM
#18
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yeah, those picse are scary...but there's got to be more to the story...
Apparently they haven't come up with a cause for the broken vanes yet. I wonder if something got in there to cause damage like that. Either that or somehow the metal suffered heat and pressure damage, almost like how cavitation can cause damage to a ship or submarine propeller.
10-09-2002, 05:30 PM
#19
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sorry, I'm missing your point........
It sounded to me like griff was suggesting his lag was turbo related which I don't belive it is. He also commented on how heat and humidity as well as elevation make a difference to power, which it does but less so in a turbo charged car than in a normaly asperated (sp?) one. Sort if two different issues.
10-09-2002, 06:29 PM
#20
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Are you saying that you don't percieve a significant increase in the rate of acceleration...
after a few thousand RPMs go by? Just wondering...
It's even more off/on on the 1.8T engine, but not at all unnoticeable to me on the 2.7T - with a stick.
It's even more off/on on the 1.8T engine, but not at all unnoticeable to me on the 2.7T - with a stick.