I took my wagon back to Bandimere Speedway in Denver, CO last nite. Elevation at the track is 5800ft above sea level.

I ran a 13.3@99 to start off the night, then hit a 13.7(misshift), and a 13.5.

For my last run, the stars aligned perfectly and everything fell into place. Here's the times....

r/t .918 <-- no.. i dont bracket race
60' 1.889
330 5.439
1/8 8.441
mph 82.12
1000 11.031
1/4 13.24
mph 102.21

Feel free to plug it into the NHRA correction factors. I personally don't like them.

This is basically a Stage4 car with a Link in place of a Unichip. Interesting what a little elevation does to the 1/4mi times no?

-jay

So you are saying that the elevation helped your times? I am confused. I was under the impression that the air at higher elevations is thinner. Making it harder for the engine to produce power? Can you shed some light on the subject for me?

BTW Good times though, but with a stage 4 setup, shouldnt your times be faster?!?!

N.1

You are making his point....

Of course his times are a little slow...he's at 5800 feet!...which was (IMO) his point. Take a mid-high 12 second car to the top of a mountain and viola, low 13 second car.

VV

Originally posted by norseone
So you are saying that the elevation helped your times? I am confused. I was under the impression that the air at higher elevations is thinner. Making it harder for the engine to produce power? Can you shed some light on the subject for me?

BTW Good times though, but with a stage 4 setup, shouldnt your times be faster?!?!

N.1

Correct.. that altitude basically sucks. On a lighter note, several stock Z06's couldn't muster their way out of the 14s on the same track last nite. Maybe that will help the comparisons a bit.

Originally posted by VetteVert
You are making his point....

Of course his times are a little slow...he's at 5800 feet!...which was (IMO) his point. Take a mid-high 12 second car to the top of a mountain and viola, low 13 second car.

VV



Yeah thats what I thought. But the nature of his post made me think that he was expecting better! BTW Phast no worries man. I can imagine what you would run at sea level!

-N.1

Originally posted by phast
Correct.. that altitude basically sucks. On a lighter note, several stock Z06's couldn't muster their way out of the 14s on the same track last nite. Maybe that will help the comparisons a bit.

Yeah Rocky mtn Raceway in Salt Lake is where I will be going. I have yet to go(I am away for the summer) and the elevation is 4500 feet or something like that. So I am not expecting much.

BTW my girl went last week and was telling me that an RSX made 10's! I said no way, especially at that altitude! I cant imagine what you would have to do to a car to make 10's at such high altitude. Esepcially an RSX.


N.1

Is it an 1/8th mile track? That's all we have around here :(

VV

Originally posted by norseone


Yeah Rocky mtn Raceway in Salt Lake is where I will be going. I have yet to go(I am away for the summer) and the elevation is 4500 feet or something like that. So I am not expecting much.

BTW my girl went last week and was telling me that an RSX made 10's! I said no way, especially at that altitude! I cant imagine what you would have to do to a car to make 10's at such high altitude. Esepcially an RSX.


N.1

Originally posted by phast
Correct.. that altitude basically sucks. On a lighter note, several stock Z06's couldn't muster their way out of the 14s on the same track last nite. Maybe that will help the comparisons a bit.

it helps, but just to add NA cars suffer MUCH more than boosted cars by altitude.

I've heard all about the 15 second C5's. I would just buy a big SUV and be done with it. On the bright side though, a moded (or even stock!) WRX would own most of the V8 cars out there (non-boosted).

-C

Originally posted by VetteVert
Is it an 1/8th mile track? That's all we have around here :(

VV



LOL! Thats the first thing I asked her. But its a 1/4. She thinks she knows everything. Like most women ;) , who knows though.

-N.1

Good time jay.

I plan on doing some low low low low 11s up here now with my new gt30.

I pulled a 13.86 with Stage 0 and VF-30 combo. There was a Viper GTS there too, his best was a 13.59 :lol: C'mon up NA guys.:devil:

Originally posted by phast
I took my wagon back to Bandimere Speedway in Denver, CO last nite. Elevation at the track is 5800ft above sea level.

-jay

Jay,
Any ideas as to what the real altitude density of the track was for the night you ran?

-Nathan

Originally posted by nmyeti


Jay,
Any ideas as to what the real altitude density of the track was for the night you ran?

-Nathan

Based on memory from the weather data on my slips and pluggin those values into the calculator at http://rshelq.home.sprynet.com/calc_hp_dp.htm

My data:
Air Temperature 70 degrees F
Altimeter Setting 30 inches Hg (guesstimate.. I'll look at the slip)
Dew Point 44 degrees F
Altitude 5800 feet

resulted in:
Relative Horsepower 80.1%
Air Density 0.9676 kg/m3
Relative Air Density 79 %
Density Altitude 7855 feet
Virtual Temperature 72.1 deg F
Actual Air Pressure 24.23 inches Hg
Actual Vapor Pressure .248 inches Hg
Relative Humidity 33.5%
Dyno Correction Factor 1.249

Nathan, Phast:

Just a note, my experience is that the temps they post on the time slips at Bandimere are about 10 deg cooler than the actual track level temps. I think their thermometer is in the tower about 30 feet above the strip.

On my first run I had an actual temp measured at the car of 89 deg, temp reported by the time slip was 76 deg, my second run I recorded a temp at the car of 87 deg the time slip temp was 75.

As far as accuracy, I'm a severe weather spotter so I've checked my thermometer on the car, against an expensive mercury meterological thermometer and it is with in a degree or so of true unless the sun is shining directly on the side of the sensor.

FWIW

Larry

Absolute Barometer quoted for our last runs was 23.38

i thought that the wastegate would compensate for the thinner air. right?:confused:

Originally posted by Red RS
i thought that the wastegate would compensate for the thinner air. right?:confused:

If you assume that the same manifold pressure can be attained at this altitude from the turbine spinning faster to compensate, then it's obviously going to take much longer to reach that given boost level. Indeed it would seem there would be a much higher boost threshold also. My guess is you'd therefore see MUCH less area under the torque and HP graphs.

Somebody correct me if this assertion is incorrect.

-Pace

The waste gate controls max boost above a preset limit

This is a common misunderstanding possibly because of how turbochargers are used on some aircraft. The plumbing on some aircraft is substantially different than that used on an automobile.

On many air craft the waste gate opening changes with altitude. It starts off wide open at sea level (ie no boost) and as the plane climbs the waste gate slowly closes so the turbo gradually creates boost to _exactly_cancel_ the effects of altitude. The result is the aircraft always acts as though it is at sea level until it reaches some critical altitude where the waste gate is completely closed. At that altitude you begin to experience loss of performance as the turbo charger can no longer provide enough boost to overcome the loss of outside air pressure.

Actually this is not turbo charging but Turbo normalized to sea level performance. An aircraft with this configuration does not increase the engine performance above its basic sea level performance. This is I believe where people get the impression that a turbo completely eliminates the effects of altitude.


On a car, and in some high performance aircraft like WWII fighter planes, the turbo is set up to substantially increase the total sea level power of the engine.

The plumbing starts out like a turbo normalized plane at critical altitude. The waste gate is closed until it is told to open. As a result as soon as some exhaust flow rate is reached to spin the turbine, the compressor starts to build boost _above_atmospheric_pressure_

when you reach some predetermined boost pressure the waste gate opens so boost does not continue to climb.

In the case of the stock turbo on the U.S. WRX it reaches critical altitude at about 13,600 ft. At this altitude even if you keep the waste gate closed all the time, it cannot achieve 14.5 psi boost.


The thing a lot of people don't understand is that a turbo actually works on a pressure ratio. If the turbo is set to achieve a pressure ratio of 2:1 ( a nominal boost of 14.7 psi), then at sealevel it will create 14.7 psi boost above _local_ atmospheric pressure.

You take the same turbo to 6000 ft and run it at the same rpm to create a 2:1 pressure ratio and you will only produce 11.78 psi of boost because that is the local air pressure you are doubling (under standard conditions).

A turbochargers output mass flow is dependent on its compressor RPM and the density of the inlet gas. Higher density inlet gas, more mass flow out.

Bottom line, a turbo makes up for about 1/2 the effect of altitude.

If a NA 400 hp engine, looses 50 hp at some altitude, a 400 HP turbo charged engine (with no changes) will loose about 25 hp at this same altitude. To a limit you can dial up the boost a bit to compensate for this, but you quickly reach a point of diminishing returns. You dial up the boost by 10%, but because of loss of effeciency the turbo might only flow 5% more lbs of air even though it creates a boost pressure that looks like it should completely compensate for the altitude. ( more heating, higher rpm, more internal friction, higher exhaust back pressure etc. all cost HP )

Its just one of those no free lunch things. Turbos reduce power loss due to high altitude, but can't completely eliminate it.

Does that make any sense ??

Larry

Originally posted by hotrod
Does that make any sense ??

Larry
Yes, that's the best explanation I've read yet. Since I run at 4100 ft, this is a big issue for me. It also explains why the NHRA correction factors for turbo cars is half that of N/A cars, IIRC.

Padre

hotrod,

Thanks for the information and explanation. Even I can understand it!

GoodFinder :)

hey nmyeti, i was jus wondering if your times from roswell were corrected of if thats what you actually ran? thanks

Originally posted by ridebmx
hey nmyeti, i was jus wondering if your times from roswell were corrected of if thats what you actually ran? thanks

Those were my actual times.

-Nathan

"Those were my actual times. "
thats very very fast.

Originally posted by ridebmx
"Those were my actual times. "
thats very very fast.

Thanks,
Some people understand, and others don't.

For the record, the night i ran 12.3@110.4 the altitude density at the track was 5800 feet.

I forget what that corrects to, but i've not been a big fan of corrected numbers for turbo cars since i don't think they are quite that accurate. However at sea level i have no doubt that i would have been faster.

Now that i've moved to Gaithersburg, and changed the setup a little bit, i am very intrested in seeing what happens now.

-Nathan

Originally posted by nmyeti
Now that i've moved to Gaithersburg, and changed the setup a little bit, i am very intrested in seeing what happens now.
So are we. :) Keep us posted.

Padre

FWIW, If I plug paces 23.38 absolute baromoet number into the formula, it comes out in the neighborhood of 16000ft altitude density. YIKES! Is there a point when that formula becomes bunk?

Phast:

When I cranked the numbers for last years Import challenge IIRC the density altitude came out to 14,000 + feet.

I think the forumla is good, because when I was in search and rescue there were days they couldn't use helicopters for rescue work at physical altitudes of 10,000 - 12,000 ft because the density altitude exeeded the limits of the Hueys, and occasionally the Chinooks and Black hawks if they had any passengers aboard. That of course makes it real difficult to lift an injured hiker and EMT's out.

Remember density altitude is the effective altitude under standard temp/pressure conditions, which is approximately 59 deg F, at 29.92 barometer at sea level if I remember.

Larry

Originally posted by hotrod

..

Does that make any sense ??

Larry

Very informative - thanks Larry. My earlier assertion was correct, then.

Jay: I saw the same thing when I plugged in the 23.38 value for absolute barometer. Given those less-than-ideal track conditions, your corrected time is very impressive indeed. Heck, even my 14.5 corrected to something like 13.4s pass. Not apalling for a complete beginner. ;) It's interesting to note that the NHRA tables I saw only go to 5500ft ASL. Has anyone extrapolated the conversions factors for 5800ft ?

-Pace

NHRA redid its high altitude correction factors, and is now only listing 6 tracks as high altitude tracks.

They have a news feature dated February 2002 I believe, on their web site if you want to look for it. They also include a note that supercharged, turbocarged cars should only use 1/2 the NA correction factor.

The correction factor for Bandimere is 1.03 for mph and .97 for ET. The actual values go to 4 decimal places but I don't have the info handy as I'm at work.

By the way Bandimere is the highest NHRA cert track.

Larry

how do you like the link?

Originally posted by hotrod

..

The correction factor for Bandimere is 1.03 for mph and .97 for ET. The actual values go to 4 decimal places but I don't have the info handy as I'm at work.

By the way Bandimere is the highest NHRA cert track.

Larry

Wow.. pretty significant difference between the n/a and turbocharged correction factors. I can't imagine they are that accurate given the lack of accounting for variance in atmospheric and track conditions, etc?

-Pace

You have to keep in mind what the altitude correction factors are for.

They help you estimate what you would have run on a specific pass, if you some how could magically move the entire strip and local weather conditions down to sea level. They don't in an absolute sense say how fast you could go at sea level only how fast a given run would have been if it had occured at sea level.

In that sense track conditions and local weather conditions are automatically accounted for.

You also have to consider some of their weak points. For example a car that is having traction / launch problems at sea level might actually run faster at altitude, because the reduced power levels let it hook up.
On the other hand a car that is just barely maintaining traction and making perfect launches at altitude might go up in smoke at sea level.

I think the best way to use them is only to get a reasonable approximation of what your "potential" performance is at another altitude, not to claim some speed/ET at another altitude. There is a big difference between I ran a 13.4 at altitude so I claim a 12.998 best ET at sea level, and saying my car "has the potential" , or "should be able to run" 12.998 at sea level.

Larry

Thanks Larry. :)

Larry, I agree. I use the correction factors as a guide just to compare with guys running similar mods at other altitudes.

However, on one occasion, I had a chance to run at 500ft (Ennis) and 4100ft (El Paso) within a week of each other with very similar conditions, and the numbers were fairly accurate.

On the other hand, my next trip to lower altitudes (Carlsbad in SoCal) didn't result in the numbers I anticipated because, as you say, there are so many other factors: track, weather, and in this case, a bad batch of gas.

Anyway, good info.

Padre

Originally posted by nmyeti


Jay,
Any ideas as to what the real altitude density of the track was for the night you ran?

-Nathan

I'm at Bandimere Speedway more than anyone. They consume my income racing 2 cars. Using a TAG handheld weather station the density altitude for the last two weeks has been between 7800-9200 Ft.

There are lots of different online calculators and of course the hand held weather stations all use slightly different algorithms. For tuning purposes the most important thing is if the system is repeatable for a specific driver and/or team.

If you plug the 6/26 numbers into this online computer (using a humidity of 10%, temp 76 , Pabs 23.38).

http://rshelq.home.sprynet.com/calc_hp_abs.htm

(one of the reasons I like this online calculator is he tells you exactly how he is calculating things )

You get an altitude of 9286 ft.

If you use my strip level temp of 89 deg for the temp you get an effective altitude of 10075 ft.

If you do a simple PV=T computation (ignoring humidity) for relative density you get an altitude of about 7484, (relative density of 0.75658) which fits well with Moorewrx's hand held when you consider the very low humidities probably contributed very little to density changes.

It really does'nt matter much as long as its repeatable for the user, and lets them make good decisions on dial-in , or tuning.

The temp and pressure calcs are pretty staight forward, but the humidy is a much more complex calculation. Most parts of the country don't ever see humidities we see routinely in the summer time. The wild fire suppression teams were absolutely stunned when at morning briefings they were told they had relative humidities of 4 % during the worst days of the Hayman Fire.

I personally wouldn't worry much about the differences. Use what works for you. Hey, in the early days Don Garlits used a candle and a fish bowl to figure tuning changes.

Larry