I figured I would post this here since it's technical and maybe some science majors might have an idea.
I know the higher you go in elevation the slower a car will run, and you have to convert your 1/4 for corrected at sea level to be "fair" to compare to other places, I guess you could say.
But why is that, how does the elevation make you slower, I know I'm thinking wrong here, but the air is thinner at higher elevations, so wouldn't that make air resistance less, meaning your car should be faster at higher elevation? So where or how am I thinking wrong here?
Thanks.

 

The answer is the thinner air has less Oxygen molecules for a given volume. Sort of the opposite of a Supercharger which crams "more air (oxygen)" in a given volume. Same with Ambient Air temp. The cooler the incoming air, the more oxygen for a given volume.

The "correction factor" means that "if you were to properly tune your engine for sea level" then you could expect to run the corrected times.

Which is another key point, IF YOUR WERE PROPERLY TUNED! An engine properly tuned for sea level is seldom properly setup for a higher elevation and vice versa. At higher elevation, your Air Fuel Tables need to change along with your spark advance. Generally, the higher the elevation, the more spark advance you can run.

This is where MAF (used on 3rd Gens) falls on it's face. The MAF sensor used on 3rd Gens makes the "corrections" based on the voltage readings it gets for both Air Temp and Elevation. While it does it "reasonably well" for "day-to-day" driving, it is FAR FROM PERFECT. A MAF car "precisely setup" for sea level, will need to be readjusted for 3,000 feet. And when it returns to sea level, it will need to be set back. Also, you cannot compensate for different spark advances as the MAF car has no "direct method" to determine elevation.

This is where SD has an advantage. While you will STILL need to retune a "perfect" SD car setup for sea level if you wish to run at 3,000 feet - you DON'T have to set it BACK to re-run when you return at sea level. This is because the VE Tables affect a specific Kpa reading which has a DIRECT RELATIONSHIP to elevation. Also, the Spark Advance is directly linked to Kpa (which is linked to elevation). Lastly, you can "tune" for ambient air temp on SD based on the MAT sensor, which you cannot do with MAF.

Don't get me wrong and think MAF cars "run like crap" when operating at a "different elevation/air temp" than what they were originally setup. It's just that they won't run "optimally" and need to be reset. And if you return, you need to reset again.

With SD, once you set it, it will work perfectly all the time. Thus you can develop an "optimal setup" for all elevations and air temps on the same chip without having to constantly reburn them.

This is a primary reason racers prefer SD.

 

Cool, thanks, I wasn't even thinking about there being less oxygen.

 

I'll add - there is less oxygen per volume, cause there is less atmospheric pressure or is the other way around. I'll let you decide

Where I live, it's around 24" @ 6300 feet aver. temp. Sea level being 29.92" aver. temp.

Ron

 

Hey

Is there a formual or anything to figure out the sea level times. I like at 3500 Feet above see level and I want to know what my car does at sea level.... Is there a formula or anything like that.

Thanks
http://camaroz28.cardomain.com/id/56424

 

Also add in a hot day at altitude and you have even less air density=less oxygen molecules for a given volume of air. Just ask a pilot about density altitude......

 

You mean like this?

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

 

Ok

so according to that site, If my car does 15.8 at 3500 feet above sea level then I would take 15.8 x .9575 so my corrected sea level time would be 15.1.... Im not sure about that. I dont think that sea level has that much to do with it. Look at that, thats taking of .7 seconds just because I live at a higher elevation. I think that it would only take of .2 seconds or so, not .7.

What do u guys think...
http://camaroz28.cardomain.com/id/56424

 

As I said in the first part of my post about "if the engine was tuned optimally". Those correction tables mean "if you were to retune your engine to run optimally at sea level". Trust me, a car tuned for 3,500 feet is NOT tuned optimally for sea level - even EFI. I've been burning eproms for over a year just "optimizing" for a variety of elevations and air temperatures.

Re-read my very first post regarding my discussions on "tuning" SD and MAF systems. BOTH need to be retuned when you change elevation for "optimal" performance - but due to the design of SD, you can make it so that it is "optimal" for all elevations on one chip and you can return to a previous elevation "you tuned optimally" without have to "retune the eprom" again. But you still need to tune it initially for a particular elevation to "optimum" performance.

And this is where these correction tables have been derived. After years of gathering data from "professionals" who "tuned" their cars "optimally" at a great range of elevations, they found the relationships in the table existed.

But, as I stated, there are other tables for air temp and humidity which also need to be corrected.

 

PS: In Kamloops, I'm around 1,200 feet. I can definitely notice the difference when I take a trip to the Coast and when I've taken trips through the Rockies.

The difference between Kamloops and the West Coast is enough that I have to pull a couple of degrees of spark advance out of the eprom to avoid detonating even when running 94 Octane.

 

Oh yeah, Calgary is renowned for its miserable "air," as racers like to call it. The density of the air at 3500 ft is a lot less than at sea level. Thicker air means more hp. Just be glad you don't live in Banff.

That's all there is to it.

 

The NHRA has conversion tables for tracks at different altitudes, so you can convert your ET & trap to the sea level equivalent; someone already posted one. There should be separate conversion tables for both altitude (which means air density) and for air temperature. And yes, both make a difference.

HRM routinely uses LACR and it's over 3000' above MSL.... so they have to convert to equivalent sea level et and trap. They also tell you clearly in each article when they do this -- to their credit.

As far as the thread comment about running faster in thinner air (at altitude), it is true that the aerodynamic drag is less. All the men's track sprint and (horizontal) jumping events were broken by large margins in the 1968 Olympics because of the altitude of Mexico City where the games were held. Most of those record stood up for years, because of the level of competition and because of the reduced air friction.

But what works for sprinters (men, women) doesn't work for cars because sprinters don't use breathed oxygen when sprinting. The O2 they use is stored on board (in the blood). The opposite was/is true for the distance races -- they were ALL slower because there was less air density.

Autos, OTOH, need air and fuel, so the performance of the engine always gets worse as the air gets thinner. And the power lost NEVER makes up for the reduction in drag.... so a car racing at altitude is always slower than at sea level. HTH, FYI. - Ken

 

That's why we call it our "altitude attitude", and:

"Mile-High Nationals".

"High-Altitude Bracket-nationals".

And why the flat-landers, when they join us for these events, are taking their engines apart after the first time trial session, trying to figure out why they lost a second and 8 mph.

Unless they know, the rest of the story...

 

hey

my buddy has a 1990 cavalier and it does 16.3. we live in calgary alberta. are u trying to tell me that at sea level his car will do 15s. I dont think so.

 

Are those ACTUAL track times, or G-Tech? I have difficulty believing he runs 16.3 at Calgary at the track.

But, IF those are his actual track times...then yes, he'd probably run 15s (per the NHRA Conversion tables) at Sea Level IF he properly tuned his engine to run optimally at sea level. That means the eprom.

Again, those tables are based on "optimal tuning" through years of experience with the NHRA. A car "tuned" for sea level will always need to be "retuned" for 3,500 feet and a car tuned to run "optimally" for 3,500 feet will need to be retuned for sea level to run optimally.

Also, at higher elevations issues like wheelspin are less of a problem as it is at sea level. This is a problem a lot of guys have that always raced at higher elevations. When they go to "sea level", the extra power now makes it more difficult to launch and find their 60' times worsen.

 

well if there set for proper tuning then u will never know what ur car runs at sea level unless u go to a track at sea level. My girlfriends dad races at race city all the time and he says that u will only lose like .2 seconds of ur time. Come on losing .7 seconds that a load of crap.

 

Well, go tell the NHRA they are full of crap and ALL the people that are posting "corrected times" they are full of crap. I personally have NOTHING to do with it and, frankly, I could care less. My bag is "tuning", not whether the NHRA correction times are "full of crap or not".

BTW, you never mentioned if that buddy with the Cavalier was a "track time" or "G-Tech time"...or is "just crap"?

 

its a track time. There was 3 other guys with him. a celica that ran 18s and some other car. So my car runs 15.4 in calgary bone stock 305 TPI, except a chip. so that means that it will run 14.7 at sea level. I dont think so

 

Again, tell NHRA...it's their correction tables. Let us know what they say.

 

I have raced at two different tracks, Atco,NJ @ 500" & Maple Grove, PA @ 1500". Both my nephews & I have noticed 3-4 tenths difference consistently between the two tracks.

 

iroc_cragg,

It seems that you have an attitude problem--NOT an altitude problem. You ask for help in understanding a problem and then tell those who know of what they speak that they are "full of crap." :nono:

This is not a healthy way to carry on social intercourse with those taking time out of their life to help you out. You are not paying anyone here to help you, so treat everyone else with a little more respect.

It is irrelevant whether you approve of there being a 7/10s of a second difference in ETs between Calgary and Vancouver. It is simply a well established scientific fact. Your OPINION is worthless in this matter.

Hey, just lighten up a bit. We all like helping you :sillylol:

 

iroc_cragg... Why can't you under stand this? I talked to a guy from Texas, we converse on camaroz28.com a bit, so one day we started calling people from across the country. We talked about the normal raceing stuff and what not. I found out why he won't post track times for his mildly modded LT1. Do you wanna know why? He said he runs low 15's to very high 14's. He is at an elevation somewhere over 3000 feet. I can't remember. (I wanna say 3900 ft.)

So what is there not to see here? Don't you understand the physics of less dense air due to elevation? Lets put it this way, try breathing through a straw... can't get enough oxygen in can you? Neither can a car at 24"Hg.

lol .2 difference?! I get that on 2 different runs.

 

*ucking 'A' bubba. I run out of breath going up the stairs up here.

Even our house furnaces have to use smaller gas jets, and more sensitive pressure switches.

Ron

 

The "standard" atmospheric pressure at sea level is 14.7 pounds per square inch. Right now where I work, at 6092 feet elevation, per calibrated instrumentation, the atmospheric pressure is 11.577 psi.

Do you think 3+ psi of boost would make a difference in how a car runs? You'd better believe it does! Same difference occurs due to atmospheric pressure.

The successful bracket racer keeps track of air density (typically expressed as altitude equivalent - a combination of atmospheric pressure, temp, and humidity) vs times because having that database and knowing the density before a run equates to what you should dial for that run - a few hundred feet elevation equivalent makes a quantifiable difference.

When I first put the 396 in the '57, I was a little disappointed that it would barely chirp the tires here. I took it to Nebraska for a high school reunion, and "discovered" that it would turn the tires all the way through 1st gear if you let it. The altitude there is 1800 feet - a 4000 foot difference from Bandimere.

Glenn has a point - setup will have to be different. I have no doubt I'd have to do something about traction, as well as tuning, to turn the times I quote as "corrected". I'd be happy to do those things, though...

 

To correct times, you really need to know the density altitude for the given time you run. Here in Minnesota, the track is ~1000ft, but corrected density altitude varies from a few hundred feet to over 5000 ft (changes of over 1000 ft can occur in just a few hours).

You'll need a weather station for that. We use the BG sportsman station (~400). Anything else is just a guess unless you know the temp, humidity and barametric pressure and then how to convert and correct for it.

Miles