Anyone have the Altitude Adjustment chart?

[plug1]

Brian, i remember you posting something about this with regards to Jeff's GTI....if you could post a link to it, i'd appreciate it. Thanks.

[Generic]

http://www.gnttype.org/techarea/misc/altitude.html

For blown and NA cars, Turbo cars aren't affected as much. To be used as a guide only.

Murdock

[exciv2000]

I like this one better:

http://www.cronusmotorsports.com/tech_info/feat_quartermile.html

It goes up to 6K feet, not just 5500 like the one Murdock posted. Besides, Bandi is at 5800 feet.

[DnVr]

according to the correction calculation

14.148 x .9276 = 13.123 et
96.23 x 1.0787 = 103.8 mph

whats the actual correction for turbo vehicles?
anyone know how much we really lose?

[phast]

Originally posted by DnVr
according to the correction calculation

14.148 x .9276 = 13.123 et
96.23 x 1.0787 = 103.8 mph

whats the actual correction for turbo vehicles?
anyone know how much we really lose?
There isn't one. WAY too many variables.

And, I will personally stab the first person that quotes "corrected" times for a turbocharged or even supercharged vehicle on this board.

*wielding knife* :Hook:

[Generic]

FYI The #'s are correct for Blown vehicles. I've tested it...a lot

2ndly, the ones I posted are the NHRA Factors (hmm, blown vehicles there) And they do go to whatever level you want, just dump the #'s in an excel file and extend the rows, it will calculate the next #'s. Its a linear increase in MPH and decrease in time.

Murdock

[phast]

Regardless.. corrected times are for ;gay;

This is HAI, we all know altitude sucks. We needn't bother correcting times to make it look better.

[V8SpankR]

The correction on a stock DSM turbo is about 8 tenths but Jay is right,too many variables. You wanna know what your car runs at sea level then go race it there.

[DlandryTSI]

Hmm sounds like I might be able to hit an 11.5@122 at sea level :)

--Dave

[john]

I am prepared to be stabbed. My car ran 10.5 @ 136 'corrected'.

RUN AWAY RUN AWAY!

Actually one of the supra guys has a forced induction "correction" calculator based on VE numbers/turbo efficiency/IC efficiency/etc. I'll go see if I can find it.

-john, about to be stabbed!


Originally posted by phast

There isn't one. WAY too many variables.

And, I will personally stab the first person that quotes "corrected" times for a turbocharged or even supercharged vehicle on this board.

*wielding knife* :Hook:

[V8SpankR]

I like it up here since I'd have to cage the car sooner at sea level plus I can beat a Z06 up here,I'm not sure I could beat one down on the flatlands.:D

[SleeperZ]

Originally posted by V8SpankR
I like it up here since I'd have to cage the car sooner at sea level plus I can beat a Z06 up here,I'm not sure I could beat one down on the flatlands.:D

:Beer: I hear that spankr! I love turbos and altitude - all the car mags test down at sea level so the "fast" car folks think they are that fast up here and get their butts kicked ;)

[newt2]

And, I will personally stab the first person that quotes "corrected" times for a turbocharged or even supercharged vehicle on this board.

When talking about roots blowers at least (not sure about the centrifugal types) altitude corrections work the same as NA motors.

[Brian]

I correct mine from time to time simply to see where my car is performance wise. I see the times the sea level guys are running and I check to see if I am up to par. my fastest run corrects to a 13.6 at sea level which is about right considering i'm still on street tires.

[phast]

I still don't understand how the roots blowers can fall into the NA correction factor. Can someone explain the physics behind that?

[V8SpankR]

I think it's because a SC spins the same at sea level as it does up here but a turbo can be made to hit the same boost up here as it does at sea level.

[shane]

huh i ran a 10.76 @125.1MPH


And, I will personally stab the first person that quotes "corrected" times for a turbocharged or even supercharged vehicle on this board



you can try, but never bring a knife to a gun fight!!!:guns:



shane

[john]

Yeah! Shane and I are in the "Corrected 10 second club"!!!

Congrats Shane! :)

[Generic]

Originally posted by phast
I still don't understand how the roots blowers can fall into the NA correction factor. Can someone explain the physics behind that?

As stated, Blowers are belt driven, therefor they can only produce so much boost. For example, my car, at sea level stock produce 6.5-7 #s. Up here, stock 4.5-5#'s I see 13#'s with this smaller pulley, in KC I saw 16+ #'s with the SAME pulley. Here's why:

The blower can only compress the air it draws in on each revolution of the motor, its RPM is fixed based on the motors RPM. Since RPM doesn't change with altitude, the air it can draw in is based on RPM and Available air. Since the available air is less, it draws in that much less each revolution (just like an NA car)

Turbo cars build to a certain boost level set by the wastegate as you know. Because the turbo isn't phsycially attached to the motor by a belt, it can spin FASTER at the same RPM level at altitude.
So, say your turbo builds to 15 PSI at 80,000 RPMs at 5,000 RPMS on your motor at sea level.
Well, up here its going to build the SAME 15PSI at 80,000 RPMS, but it will take long, say 5,200 RPMS on motor to get there.

Turbo car produce the same PEAK power at sea level as at altitude, its the lag time that increases with altitude. The power curve is shift up in the RPM band on the motor.

Clear as mud right?

Murdock

[phast]

Gotcha...

I still stand by my original threat about posting "corrected" times.

:D

[Generic]

Oh, I know, I don't :)

Murdock

[shane]

Yeah! Shane and I are in the "Corrected 10 second club"!!!



thanks john, congrats to you too:cool: heres to the "corrected" time club:Beer:


some day i will make a run at sea level..................................... and just disapoint myself.


shane

[davidm_sh]

Originally posted by Generic


As stated, Blowers are belt driven, therefor they can only produce so much boost. For example, my car, at sea level stock produce 6.5-7 #s. Up here, stock 4.5-5#'s I see 13#'s with this smaller pulley, in KC I saw 16+ #'s with the SAME pulley. Here's why:

The blower can only compress the air it draws in on each revolution of the motor, its RPM is fixed based on the motors RPM. Since RPM doesn't change with altitude, the air it can draw in is based on RPM and Available air. Since the available air is less, it draws in that much less each revolution (just like an NA car)

Turbo cars build to a certain boost level set by the wastegate as you know. Because the turbo isn't phsycially attached to the motor by a belt, it can spin FASTER at the same RPM level at altitude.
So, say your turbo builds to 15 PSI at 80,000 RPMs at 5,000 RPMS on your motor at sea level.
Well, up here its going to build the SAME 15PSI at 80,000 RPMS, but it will take long, say 5,200 RPMS on motor to get there.

Turbo car produce the same PEAK power at sea level as at altitude, its the lag time that increases with altitude. The power curve is shift up in the RPM band on the motor.

Clear as mud right?

Murdock

That is Exacally the way I understand it. Except i would like to add one thing. When it comes to supercharged cars I always thought they got kind of a "double whammy" in terms of performance.

Here is why I think that. As Generic already explained he loses about 3psi up here (boost levels) becuase of the thinner air. BUT the kicker comes in in that EVERYBODY (NA, supercharger, turbo)loses another 3psi becuase the atmospheric pressure is about 3psi less as well.

So in reality it would seem:
-a supercharged car would feel like it loses 6 psi = 3psi loss from blower + 3psi loss from ambient atmospheric conditions.
-where as a NA or turbo car would only lose the atmoshperic 3psi loss. You could theoritically make up for it a bit with a turbo car by turning up the boost. But somthing I am starting to think about is that your fuel curves would get messed up (ie; leaned out) becuase the ECU figures out correction factor for that 3psi atmospheric loss and makes proper A/F fuel changes. At least with my piggy back system I have to run the same boost levels as I did at sea level or my unichip tune could get messed up.

Now someone, like phast, with a standalone probably has the best chance to "make up the difference" as they can tune their A/F all they want too.

ANyway enough rambling.... All I know is even running the same boost levels at sea level and here ONCE the boost finally hits (is laggier up here and less off boost power) it feels about the same to my butt dyno... or maybe it's my grin factor [heh] :).

[Generic]

Well, your thinking of the Blower/Motor as two seperate units. You have to think of them as one big air pump. 3 PSI is 3 PSI for the entire unti, not for the motor, and 3 PSI more for the blower :)

Murdock

[davidm_sh]

Ok I am still confused. Let me try and explain me understanding of it this way:

-At sea level you have:
total pressure = atmospheric + boost from supercharger
total pressure = ~14.7psi + 16psi (in KC like you said) = 30.7psi total air pressure in the manifold

-Now at 6000 ft. above sea level ala The Springs you have:
total pressure = atmospheric + boost from supercharger
total pressure = ~11.7psi + 13psi = 24.7psi total which is about 6 psi less than at sea level.

Now I am not saying I am correct but this is my understanding of how things work in a supercharged car from what you and others have said.

In turbo and NA cars they lose the 3psi from atmospheric but Turbo cars don't lose an additional 3psi becuase they can always "try" and hit their target boost ... ignoring other technical disscussions of that topic ;).

Let me know what you think

[phast]

Originally posted by davidm_sh



Now someone, like phast, with a standalone probably has the best chance to "make up the difference" as they can tune their A/F all they want too.



Sounds good in theory, but it has alot to do with the madman at the laptop punching all the numbers. Something I haven't been able to do sucessfully ...... yet!

[newt2]

Ok I am still confused. Let me try and explain me understanding of it this way:

-At sea level you have:
total pressure = atmospheric + boost from supercharger
total pressure = ~14.7psi + 16psi (in KC like you said) = 30.7psi total air pressure in the manifold

-Now at 6000 ft. above sea level ala The Springs you have:
total pressure = atmospheric + boost from supercharger
total pressure = ~11.7psi + 13psi = 24.7psi total which is about 6 psi less than at sea level.

Now I am not saying I am correct but this is my understanding of how things work in a supercharged car from what you and others have said.

In turbo and NA cars they lose the 3psi from atmospheric but Turbo cars don't lose an additional 3psi becuase they can always "try" and hit their target boost ... ignoring other technical disscussions of that topic .

Let me know what you think

I think you pretty much hit the nail right on the head.

[exciv2000]

Originally posted by davidm_sh
Ok I am still confused. Let me try and explain me understanding of it this way:

-At sea level you have:
total pressure = atmospheric + boost from supercharger
total pressure = ~14.7psi + 16psi (in KC like you said) = 30.7psi total air pressure in the manifold

-Now at 6000 ft. above sea level ala The Springs you have:
total pressure = atmospheric + boost from supercharger
total pressure = ~11.7psi + 13psi = 24.7psi total which is about 6 psi less than at sea level.



I'm not siding with anyone here, because I don't know the true answer, but Generic said to think as the blower and the engine as one big air pump, which would be:
-total pressure = ~11.7psi + 16psi = 27.7psi total which is about 3 psi less than at sea level.

Because the engine only has 3 PSI less of atmospheric pressure, it therefore only shows 13 PSI on the boost gauge.
FWIW, on my M45, I can get 5.75 PSI roughly here at altitude on the boost gauge, but that's at 6500 RPM and above.

[davidm_sh]

Originally posted by exciv2000


I'm not siding with anyone here, because I don't know the true answer, but Generic said to think as the blower and the engine as one big air pump, which would be:
-total pressure = ~11.7psi + 16psi = 27.7psi total which is about 3 psi less than at sea level.


The only thing I disagree with you on is that you state 16psi with the 6000ft. above sea level equation which is not what Generic said. Generic stated that he only sees 13psi on his boost gauge. Remember a boost gauge only shows RELATIVE boost NOT absolute boost. So it does not factor in the loss or gain in atmospheric conditions. It only shows relative boost to what the atmospheric conditions are. Does that make sense... I hope it does :).

I just want to try and keep this clear becuase if I am wrong or right I want to beable to see where exacally.

Originally posted by exciv2000
Because the engine only has 3 PSI less of atmospheric pressure, it therefore only shows 13 PSI on the boost gauge.
FWIW, on my M45, I can get 5.75 PSI roughly here at altitude on the boost gauge, but that's at 6500 RPM and above.

Have you ever driven your car down to sea level or near there and noticed any difference in your boost readings? Just curious. Becuase everyone I have heard from, like Generic, reports a 2-3psi difference (with the same size pulley) between here and sea level.

I have heard of the 6psi JRSC kits on various Honda's producing more boost like 8-9psi MAX (at upper rpms) becuase some people use the stock exhaust/exhaust manifold, etc and therefore get more back pressure which leads to higher boost numbers in the intake (ie: the system gets backed up and therefore builds more boost). I just mentioned this as too maybe why your system shows near 6psi at a certain point?? Just a thought.

[exciv2000]

Well, when it's colder it gets closer to 6 PSI, I should have mentioned that too. I'd be lucky to see 5.75 roughly on the boost gauge when it's 80* outside. The only thing restrictive on my car is the cat at this point.

Generic may be seeing 13 PSI rather than say 15 PSI at altitude because his blower is larger than mine, his pulley is different, the manifold that he is compressing the air in is different, and his engine is different... in fact, the only thing our engine/blower combos have in common is it has an eaton blower attached to it.

No, what you said about relative vs. absolute doesn't make a whole lot of sense to me. I guess I'm not sure how a boost gauge reads boost, because you have to have air to make air, correct? So an SC and a turbo both pull in more air and compress it to fit into the same internals of the engine... What I mean by this is my car was N/A, but I'm forcing more air into those same N/A cylinders, so therefore I need more air coming through the intake tract before the blower. The fact that we live at 6000 feet above sea level means that we get less oxygen, about 3 PSI less. So in the case of my car, the SC is still doing the work of 6 PSI no more, no less, given the characteristics of the pulley size and the rotors inside, but the boost gauge isn't going to measure that, because that would be absolute, right? In the case of Generic's car, if he has a 16 PSI pulley, and he's seeing 13 PSI on the gauge, that 3 PSI is going somewhere... perhaps his blower is less efficient, or his boost gauge is fux0red, or maybe it's still working at 16 PSI, but since he's got 3 less PSI to work with in the form of atmospheric pressure, his gauge shows 3 less PSI as well... That would be relative, would it not?

[Brian]

As stated earlier a blower is simply a mover of air. It does little to no compressing, it simply moves a fixed volume of air per revolution. That being said I make about 9 psi on the 10 psi pulley up here. Most sea level guys with similar mods make 12 psi or so telling me that I lose around 3 psi. The closest to sea level I have been is about 3500 feet where I made nearly 11 psi according to my gauge.

[exciv2000]

yeah, it moves air, so does a turbo. a turbo compresses the air it moves, so does a blower, just in a different way. There is little to no compression of the air inside of the blower, correct (unless it's a lysolm SC(or centrifugal for that matter)), but the compression happens when all that air is "moved" into the manifold during boost. If it was just simply a mover of air, you'd see 0 on your boost gauge at WOT, and you'd make just the same amount of power as you would N/A. But your blower moves more air in then the engine would injest in vacuum, and since that air has to go somewhere for you to make power, it compresses into the manifold until one or both of the valves open to accept MORE of that air then you'd be putting in there N/A.

[milehighz28]

Err, well, I guess Im about one of the only NON boosted cars around here. :) Makes it easy for me.

12.374 @ 110.61 at sea level.

Now, I hope I dont get stabbed, I am NA after all....

[Mark_H]

I've been using those charts for years. Those charts come in handy to keep yourself from being flamed on other message boards when you post timeslips etc. You can atleast back yourself up and explain how altitude affects times so much here.
M