Blasted some more...

[ismellfish2]

TurboDan is racing n/a cars at elevation of 5500 feet so he has a huge advantage with his turbo car.

It's even worse for the NA cars because of density altitude. Density altitude can be loosely thought of as the apparent altitude (what the engine thinks it's operating at) vs true altitude referenced to Mean Sea Level "MSL". Density altitude is what aviators use to understand aircraft performance during nonstandard conditions. Standard altitude in the US is based on a standard of 29.92" HG and 68 F. air temp at 0% humidity. For aviation / performance calculations density altitude calculations are based a two measurable values, pressure altitude (1 BAR ~15 psi reference) and air temperature. Since I happen to have my handy E6B whizwheel I ran a quick exercise to see how non-standard temps impact DA when pressure is constant. If the airtemp increases from 15C (~60F) to 27 C (~80F) you'll see a DA of about 3000 ft. So in Houston which is about 50 ' MSL at 80F the engine thinks it's at ~ 3000 ft.

Extrapolate this DA increase to Denver and you quickly can see that a NA car's engine is seeing a DA of ~ 8500' not 5500 '. In aviation circles there's a rule of thumb that 75% power will be seen at about 7500 ' of altitude during standard conditions. So you can see that at Denver altitudes during a standard day you'll only make about 80% of the theoretical HP. If the outside air temp are above standard conditions the performance will suffer even further.

Depending on how well Dan's turbo car is running he might have HP values comparable to some pretty high HP NA cars.

Rich

I'm not sure I completely understand. Air pressure decreases directly corresponding to feet above sea level, and besides that, humidity and high temperature dilute and reduce the amount of air per volume. But do you think 80F is a more realistic input for temperature in Denver than 60F? Even if not I guess your value might stand if it were made up for by humidity being above 0- I don't know how the sensitivity to change in humidity compares to the sensitivity to temperature.

But don't these factors apply to Dan as well? It seems like everybody else is clear on this, but I'm not... isn't his boost just above ambient air pressure? I'm not sure why the thin air is assumed to affect only NA cars and is an advantage for a turbo.

Also, I think you went the wrong direction estimating the power percentage remaining at elevation. If you've got 75% at 7500, you would expect the effect to be more pronounced as effective elevation continues to increase, so DA = 8500, power would be even lower, maybe 70%. But then you went on to say that if air temps were higher the effect would be even more, so maybe the 80% is humidity adjusted? I'm not sure what you were doing there.

Not to pick you apart, you made an interesting point there. I'm just curious. I've been working with gravity anomalies some, which are similar. Also, I'm about to fly to 5000 feet, and I hope to get up to near twice that, so it'd be nice to know exactly why I'm feeling so shitty!

[Tammer in Philly]

Also, I'm about to fly to 5000 feet, and I hope to get up to near twice that, so it'd be nice to know exactly why I'm feeling so shitty!

While you're feeling so shitty is that the partial pressure of O2 seen at your lungs is much lower than normal, so your hemoglobin isn't binding oxygen as effectively. The altitude pushes the equilibrium towards the unbound state.

-tammer

[turbodan]

I'm not sure I completely understand. Air pressure decreases directly corresponding to feet above sea level, and besides that, humidity and high temperature dilute and reduce the amount of air per volume. But do you think 80F is a more realistic input for temperature in Denver than 60F? Even if not I guess your value might stand if it were made up for by humidity being above 0- I don't know how the sensitivity to change in humidity compares to the sensitivity to temperature.

But don't these factors apply to Dan as well? It seems like everybody else is clear on this, but I'm not... isn't his boost just above ambient air pressure? I'm not sure why the thin air is assumed to affect only NA cars and is an advantage for a turbo.

Also, I think you went the wrong direction estimating the power percentage remaining at elevation. If you've got 75% at 7500, you would expect the effect to be more pronounced as effective elevation continues to increase, so DA = 8500, power would be even lower, maybe 70%. But then you went on to say that if air temps were higher the effect would be even more, so maybe the 80% is humidity adjusted? I'm not sure what you were doing there.

Not to pick you apart, you made an interesting point there. I'm just curious. I've been working with gravity anomalies some, which are similar. Also, I'm about to fly to 5000 feet, and I hope to get up to near twice that, so it'd be nice to know exactly why I'm feeling so shitty!

The same factors do affect turbo cars. But, in my case, I'm boosting Exactly as much as I can, which makes up for a great deal of it. The clutch is barely holding on at 12 psi. Atmospheric pressure is about 12.5-13 up here between 5000, around the valley and the Rio Grande and 5800 feet, along Tramway at the base of the Sandias or on east Paseo near Tramway.

So, 12 psi above atmospheric pressure is between 24.5 and 25 psi in the manfold. I would only need to make about 10 psi at sea level to make the same amount of pressure in the manifold. Its also important to note that I could only be boosting about 10 psi at sea level, which puts me right on the detonation threshold. If I ran the same 12 psi at sea level, it would be the same manifold pressure as if I were running 14 psi up here. Until I get some cooler plugs, I dont think I can do that.

I don't really worry about air temps up here. I dont have an AC right now, so don;t really drive too much when its hot out. I like to go out and play at night, when its usually between 70 and 80 degrees. Not so bad.

[shifty]

Dan,

I may have missed it, but what are you using to tune that ita beast?

[turbodan]

Dan,

I may have missed it, but what are you using to tune that ita beast?

I'm using a Cartech 2025 RRFPR, 535 injectors, a split second MAF and ARC2 box on the drivers side under-dash panel. I'm thinkin about megasquirt, but I don't know if I really need to do that yet.

[Rich Euro M5]

I'm not sure I completely understand. Air pressure decreases directly corresponding to feet above sea level, and besides that, humidity and high temperature dilute and reduce the amount of air per volume. But do you think 80F is a more realistic input for temperature in Denver than 60F? Even if not I guess your value might stand if it were made up for by humidity being above 0- I don't know how the sensitivity to change in humidity compares to the sensitivity to temperature.

You are correct in theory, under standard conditions you should see a standard lapse rate in temperature and pressure as altitude increases. The problem with the atmosphere is it doesn't follow the rules. It's not unusual to have temperature inversions in which the surface air temps are cooler than at altitude.

About humidity, it does do as you state, decrease air density simply due to the water vapor molecules displacing air molecules. However the E6B whizwheel simply dismisses the humidity "Vapor Pressure" and simply uses the pressure altitude in combination with airtemp. The flaw with doing this is the errors can be quite high, upwards of 10%.

For example if you use the full equations for calculating Density Altitude which includes the Vapor Pressure. On a hot, rainy summer afternoon in Colorado, 95 deg F with a dew point of 95 deg, (100% saturation) at an altitude of 5050 feet and an altimeter setting of of 29.45 , the actual pressure is 24.445 in-Hg and the actual Density Altitude is 9753 feet. Yet calculating the Density altitude using the simplified equation "E6B Method" gives a result of 8933 feet.... an error of 820 feet.

As you can see Denver isn't the place to be racing a NA anything against a car of much less stature with forced induction.

The thing to remember is my original example is simply an guestimate used in aviation circles to determine aircraft performance. It's nice to know if you have enough runway and/or engine performance to get off the ground.

ismellfish2 wrote:
Also, I'm about to fly to 5000 feet, and I hope to get up to near twice that, so it'd be nice to know exactly why I'm feeling so shitty!

While you're feeling so shitty is that the partial pressure of O2 seen at your lungs is much lower than normal, so your hemoglobin isn't binding oxygen as effectively. The altitude pushes the equilibrium towards the unbound state.

-tammer

Tammer is correct, your suffering from the onset of hypoxia. If you are a smoker the effects are worse, as you're cruising at about 5000 ft when you're at sea level due to the effects of your habit. Add 5000 ft of altitude along with density altitude effects and a smoker could have a pretty difficult time in Denver, Co. A simple fix is to breath supplemental oxygen via a nasal cannula or medical O2 mask. This works fine up to about 25,000 ft. At this altitude even breathing 100% O2 isn't enough, the gas doesn't have enough pressure to transfer efficiently across the membranes of your lungs. At this point you need a sealed O2 mask like you see military pilots wearing, breathing O2 under pressure.

HTH

Rich

[Nebraska_e28]

I'm not sure I completely understand. Air pressure decreases directly corresponding to feet above sea level, and besides that, humidity and high temperature dilute and reduce the amount of air per volume. But do you think 80F is a more realistic input for temperature in Denver than 60F? Even if not I guess your value might stand if it were made up for by humidity being above 0- I don't know how the sensitivity to change in humidity compares to the sensitivity to temperature.

You are correct in theory, under standard conditions you should see a standard lapse rate in temperature and pressure as altitude increases. The problem with the atmosphere is it doesn't follow the rules. It's not unusual to have temperature inversions in which the surface air temps are cooler than at altitude.

About humidity, it does do as you state, decrease air density simply due to the water vapor molecules displacing air molecules. However the E6B whizwheel simply dismisses the humidity "Vapor Pressure" and simply uses the pressure altitude in combination with airtemp. The flaw with doing this is the errors can be quite high, upwards of 10%.

For example if you use the full equations for calculating Density Altitude which includes the Vapor Pressure. On a hot, rainy summer afternoon in Colorado, 95 deg F with a dew point of 95 deg, (100% saturation) at an altitude of 5050 feet and an altimeter setting of of 29.45 , the actual pressure is 24.445 in-Hg and the actual Density Altitude is 9753 feet. Yet calculating the Density altitude using the simplified equation "E6B Method" gives a result of 8933 feet.... an error of 820 feet.

As you can see Denver isn't the place to be racing a NA anything against a car of much less stature with forced induction.

The thing to remember is my original example is simply an guestimate used in aviation circles to determine aircraft performance. It's nice to know if you have enough runway and/or engine performance to get off the ground.

ismellfish2 wrote:
Also, I'm about to fly to 5000 feet, and I hope to get up to near twice that, so it'd be nice to know exactly why I'm feeling so shitty!

While you're feeling so shitty is that the partial pressure of O2 seen at your lungs is much lower than normal, so your hemoglobin isn't binding oxygen as effectively. The altitude pushes the equilibrium towards the unbound state.

-tammer

Tammer is correct, your suffering from the onset of hypoxia. If you are a smoker the effects are worse, as you're cruising at about 5000 ft when you're at sea level due to the effects of your habit. Add 5000 ft of altitude along with density altitude effects and a smoker could have a pretty difficult time in Denver, Co. A simple fix is to breath supplemental oxygen via a nasal cannula or medical O2 mask. This works fine up to about 25,000 ft. At this altitude even breathing 100% O2 isn't enough, the gas doesn't have enough pressure to transfer efficiently across the membranes of your lungs. At this point you need a sealed O2 mask like you see military pilots wearing, breathing O2 under pressure.

HTH

Rich

Damn! With all the knowledge you guys have, I'm in the wrong profession. Either that or just too darn young to have experienced everything!!

[bIGjake]

man, you guys like went to college or something, i mean, its a CAR FORUM not some damn atmospheric condition forum, so take off the scolar hats, put on ur overalls, and stop fucking arguing, you all are making uselves look like total dick heads, i hope you dont go about accusing people of shit like that all the time, its depressing, now stop tormenting turbodan, he knows his shit, i dont see you guys building a turbo kit from scratch, if thats what its all about, a homebuilt bimmer takin a c5 to school, not a false accusation, so, thats my 2cents

[shifty]

man, you guys like went to college or something, i mean, its a CAR FORUM not some damn atmospheric condition forum, so take off the scolar hats, put on ur overalls, and stop fucking arguing, you all are making uselves look like total dick heads, i hope you dont go about accusing people of shit like that all the time, its depressing, now stop tormenting turbodan, he knows his shit, i dont see you guys building a turbo kit from scratch, if thats what its all about, a homebuilt bimmer takin a c5 to school, not a false accusation, so, thats my 2cents

[Boru]

man, you guys like went to college or something, i mean, its a CAR FORUM not some damn atmospheric condition forum, so take off the scolar hats, put on ur overalls, and stop fucking arguing, you all are making uselves look like total dick heads, i hope you dont go about accusing people of shit like that all the time, its depressing, now stop tormenting turbodan, he knows his shit, i dont see you guys building a turbo kit from scratch, if thats what its all about, a homebuilt bimmer takin a c5 to school, not a false accusation, so, thats my 2cents

College? Most, I would say though it doesn't matter.

Car Forum? Not entirely.

Atmospheric condition forum? I like running mine in some form of atmosphere, therefore it's applicable.

Depressing? Only for the overly sensative... read "you".

Tormenting? No, questioning. Answers are derived this way.

Built from scratch? Many have and some have built many. Now, by "from scratch" do you mean buying parts or starting with a pattern, green sand and molten iron?... cause a couple here went that route.

If you respond please try to use capitalization and an attempt at spelling out entire words. Us cawledge gradgiates think it's gooder that way.

[Shawn D.]

man, you guys like went to college or something, i mean, its a CAR FORUM not some damn atmospheric condition forum, so take off the scolar hats,

Yes, some of us "like" went to college, some went to college, some graduated, some are graduate students, some are (or have been) aviators, and/or have real-world experience with meteorology. You seem to think this is about class warfare, which could not be further from the truth. FYI, it's spelled "scholar."

stop fucking arguing, you all are making uselves look like total dick heads,

No, you are making yourself look like one with that post.

[Tammer in Philly]

man, you guys like went to college or something, i mean, its a CAR FORUM not some damn atmospheric condition forum, so take off the scolar hats, put on ur overalls, and stop fucking arguing, you all are making uselves look like total dick heads, i hope you dont go about accusing people of shit like that all the time, its depressing, :bawl: now stop tormenting turbodan, he knows his shit, i dont see you guys building a turbo kit from scratch, if thats what its all about, a homebuilt bimmer takin a c5 to school, not a false accusation, so, thats my 2cents

Yay, let's glorify ignorance! Let's all be stupid! Let's align ourselves with the lowest common denominator so no one's feelings get hurt!

If you don't understand the discussion, you have two options:

1) Get out a fucking dictionary and start learning something.
2) Ignore it.

Other than that, no one wants to hear what you have to say. Some of us have worked hard to learn what we know, and always try to learn more. The vilification of those that do so as "elitists," "intellectuals" (in a disparaging context), and "snobs" is one of the most disturbing trends in modern America. It comes from the same idiots who want to ensure that their kids never feel inferior to anyone else. Well guess what, once they're out of high school they're gonna realize just how inferior they are, and what's more, as a result of the hand-holding they'll lack the resources to overcome any obstacles they encounter. Idiots raising idiots. Take that line of bullshit somewhere else.

-tammer

[Nebraska_e28]

I'm usually enlightened by the intellectual diaspora that is regularly displayed here. The only downside is whenever it turns into a pissing match, or it flies so far over someone's head that they return ignorant comments of no sustenance! Fellas, let the knowledge flow..

[bIGjake]

[Azure]

I was actually enjoying the talk of atmospheric pressure in an NA vs FI application, I'd never given it any thought before.

[SheerHippo]

Well that's true, at high altitudes you'll pretty much demolish any NA car up there since you can compensate for the thin air, but they can't. I was about to say, there's no way you'd be able to beat a car with roughly the same weight, better aerodynamics, more grip, and more HP/torque...from a bench racers perspective it just doesn't add up. But, you're all the way...up there...lucky

[turbodan]

Its not totally unfair. We're only talking about maybe 20% on a cool night. So the Z06 is making 320 instead of 400. Still, not bad considering the aerodynamic disadvantage.

[SheerHippo]

Oh it's totally fair, gotta be able to adapt to a different environment right? Anyway with that being said, even with the horsepower loss, I think that because of the lower drag coefficient of that 'vette, it would have been a tough race to win had it started at high speed...did it? Congratulations though, you must have one fast 528e...shun the non-believers!