Density Altitude / Speed

[bak189]

Boy, all this info. is to much for this old mans brain to absorb.........but this I do know......we ran our sidecar (back in 1991) at Bonneville at max.
164mph. without a passenger (using a KZ .Kawa Turbo).... put it in the trailer.....drove to New York.......put the trailer on the ship.......picked the whole mess up in Rotterdam.....took it to a Speed Trial (100 feet level)......same gearing, same boost, same fuel, same everything,...this time with a passenger.....ran 187mph......on PAVEMENT.......
I have always assumed  it was traction that made the diff.  May have been a combination of all
conditions......certainly humidity in the air would have made a diff.   

[RidgeRunner]

     A few table scraps for thought.

     I was an bystander at an interesting discussion as 2 air density meters [same brand and model] lay side by side on the salt in early '70's with 2 very different readings.  The 2 owners said they had gotten readings very close to each others at Lions.........   Some heavy hitters present, photos taken, no conclusions arrived at that I remember or heard of afterward.

     I have often wondered how much difference in the air composition in the first few feet off the surface of the salt under different conditions.  Height of water table/salt surface condition and air conditions/composition at higher elevations.  Is the air coming into an intake a foot or so off the surface enough better [more moisture/dense] than one off the top of a roadster hood enough better for a bit of free HP lunch?

     Overheard a comment by an experienced [50 years or so in motorsports of many forms] observer [guesstimate on site at both venues for runs numbering well into the 5 figures total over the years] that as general rule of thumb vehicles ran 80% of their B'ville speed at Maxton.
     
                                                                                                Ed Purinton

[Freud]

Use the blower and run at Bonneville unless you have a bigger blower and run in South America at 10,000 feet. You just won't have enough horsepower to walk to the car and back to the push truck.
FREUD

[Flyboy]

We seem to be getting off topic with blowers. The question deals with naturally aspirated engines.  In my best guestimation I say one loses 5-7% top speed by running in the salts as compared to sea level with the differences in density altitude. Therefore a 200 mph speed at Maxton would run around 187 mph at Bonneville and a 200 mph run at Bonneville would be approximately 212 mph at sea level.

Comments or opinions?

[JackD]

Density of the tuner/builder and altitude of the operator have a lot to do with the results in any condition
.
"The  Wise Old Fox is still going to eat the scientifically bread chicken."

"One variable does not a total result make."

[Sumner]

Therefore a 200 mph speed at Maxton would run around 187 mph at Bonneville and a 200 mph run at Bonneville would be approximately 212 mph at sea level.

Comments or opinions?

Isn't that what I said up above  .

But like the others have said there are too many varaibles to do what you are trying to do.  Best thing is to run at both.

Here is info I posted last Aug. that might give you an idea of the changing conditions:

Day....Time......Humidity..Density Altitude...Temp.

8-12...1:07pm.....21%.........6820 ft.............81 deg     
8-12...5:54pm.....13%.........7407 ft.............90 deg
8-13...5:43pm.....13%.........8160 ft.............83 deg
8-14...3:02pm.....16%.........7977 ft.............89 deg
8-15...11:59am...17%.........6867 ft.............84 deg
8-16...10:32am...13%.........6350 ft.............76 deg
8-17...7:17 am....26%.........5707 ft.............64 deg
8-17...2:24 pm....13%.........6711 ft.............84 deg
8-17...4:57 pm....11%.........6794 ft.............85 deg

You can find all of the rest here:

http://www.landracing.com/forum/index.php/topic,1506.msg16410.html#msg16410

Hope you go back an read it.  Took me 20 minutes to find it ,

Sum

[Flyboy]

Sum--

Thank you for your effort but I realize the DA changes hour to hour and it's hard to compare apples with apples. That's why I mentioned a typical average DA on the opening notation. Maxton 1,928 ft. DA and Bonneville 6,739 ft. DA. which through research and guestimation showed a typical reading in both locations at roughly the same time of the day.

In summation, running at Bonneville does not show the true top speed numbers of our vehicles as compared to running at sea level. And I am not referring to turbo charged vehicles.

[interested bystander]

I'm thinking there may be more to the D/A thing that meets the eye.

Whyzit that the bicycle people going for speed records race at Battle Mountain, Nevada at somewhere between 4000 and 4500 feet and not below sea level at Death Valley on a nice spring  day?

Could it be the reduction in AERO DRAG offsets the reduced horsepower being generated by the HUMAN powerplants that propel them?

And why didn't the unlimited air racers not fly as fast when they raced at Hamilton Field on S.F. Bay (or was it San Pablo Bay?) (sea level)  as they do at RENO (abt. 4000 ft.)?

Point is, the performance difference MAY not be just the difference in breathing (AND, of course, traction available).

Any comments Rex? PorkPie? Bernoulli? Newton?  Railton? Kelly Johnson?

[tortoise]

Whyzit that the bicycle people going for speed records race at Battle Mountain, Nevada at somewhere between 4000 and 4500 feet and not below sea level at Death Valley on a nice spring  day?

Could it be the reduction in AERO DRAG offsets the reduced horsepower being generated by the HUMAN powerplants that propel them?

Read ack's post. The HPV motors, aka leg muscles, are more like turbocharged motors than naturally aspirated. The limiting factor is not the lungs, but the heart and muscles. For short bursts, muscles also work anaerobically, using oxidants stored in the muscles. By the way, the optimum altitude for bike records is apparently higher than Battle Mountain. Eddy Merckx set the one hour record for bicycles at a velodrome in Mexico City at about 7500 ft.

[Flyboy]

From my limited knowledge they go to Battle Mountain because 1) the air is thin offering less resistance and 2) The hills block the wind. I also understand they train months in advance at high altitudes (10,000 feet +) just like marathon runners, to enlarge their lungs so when they drop down to altitude they will have better "blowers". (there is no sexual meanings here- think air/fuel ratio)

Death Valley is located on the edge of Owens Valley which has some of the strongest winds in the country. Many airplane and sailplane drivers go to this area to set altitude records because of the updrafts. When it doesn't blow it's 120 degrees and I'm sure quite a high DA.

The unlimited planes go faster at Reno/Stead airport 5550 ft (5,050 ft plus 500 feet racing altitude) because they're supercharged.

[Dean Los Angeles]

The unlimited planes go faster at Reno/Stead airport 5550 ft (5,050 ft plus 500 feet racing altitude) because they're supercharged.

Are you sure? It LOOKS like 5,051 feet when you are standing there watching.


Check out Dolan's new car:

[JackD]

That is the old car powered by processed pinto beans and hard boiled eggs.
I convinced Kent to hold the match.
The new one is motivated by corned beef and cabbage in honor of St. Pattie's day.
Because Kent was no longer available, Freud stepped up.
The DA was remarkable.
We call it the "Plopster".

[Dynoroom]

I prefer it closer to the ground. 

[interested bystander]

We're probly getting way off the subject, or are we? (This horse could be dead).

My query a post or two back was intended to get some positive data -love yer tag, dynoroom- that density altitude is not the ONLY indicator to one's increased (or decreased) performance at differing altitudes.

I understand somewhat anerobics re- athlete performance, but think its more like stored energy (batteries) than "turbocharging".

And I KNOW that unlimited airplanes (worked on a couple) are supercharged at Reno- they were at Hamilton Field, also.DUH.

Death Valley was only in the 70's today.

Why do they hit lots of homers at Coors Field? Can it be the anerobic condition of the ballplayers. Doubtful, as all they do is stand around, spit and scratch like at every ballpark on the planet. Probably not the supercharging effect of Coors, either. 

Maybe it's the thinner air!

THAT'S THE POINT MY POSTS HAVE BEEN TRYING TO ESTABLISH!

With DATA, not BS, whoops, I meant opinions.ANYBODY?

[tortoise]

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