Dyno-Facts or Fiction?

[Herr-Kuhn]

Here is an interesting read on dynos and the variability in the results obtained based on the type.

http://www.germanmotorcars.com/Dyno_load%20vs%20inertia_1.htm

Happy reading

[Danglerb]

Gtech FTW

[rhjames]

suggest you re-read the paragraph where the author talks about altitude....

"the engine doesn't care what altitude it's tested at"

probably, and the author goes on to say that (28. whatever) barometric pressures at sea level are the same at 4000 ft up.

true again.

then the author says that when on the track, the car makes much less power at high altitude than at sea level.

why is this? BECAUSE THERE IS LESS OXYGEN IN HIGH ALTITUDE THAN AT SEA LEVEL-- -IN THE SAME VOLUME OF AIR.


that's why you can't run the same amount of fuel at high altitude as you can at sea level in a race engine (or any other engine for that matter) and expect to get the same power and performance.


the author seems to have trouble in grasping this concept in the relationship with dyno's......


interesting, but not quite there---


---rhj

[Herr-Kuhn]

RH...What he said was the engine dyno attempts to correct to spit out a sea level corrected number...it is in there you just have to search for it. His statements about altitude were qualified by stating that if barometric pressure was equal at two different altitudes the end result is the same.

The amount mass per unit volume is not a function of altitude, but barometric pressure. Barometric pressure is a function of altitude.

I've done some reading on Dynojet vs. Mustang load units...it seems as though the Mustang units generally report back a number which is 10% lower than Dynojet. Good news for me since my torque is already at 460+ ft-lbs on the 32V car out of the Mustang dyno on a low 8 psig.

Oh, did I mention that turbochargers will seek the same basic boost level regardless of the altitude?

[rhjames]

try again--

barometric pressures are not a function of altitude, as you can have the same pressures at sea level and at Denver (el" 5280 ft).

if you were correct in your statement, you would only have tornados in coastal areas, not the high plains of Texas up through the Midwest------think about it.

ask the ProStock guys what size jets they run in their cabs at sea level, and then what they run at Mile High in Denver......

you will find that to make the same HP in both arenas, they must use some sort of supercharger (illegal in ProStock) to compensate for the "thinner air" at high altitude.

how do they make their cars work at Mile High? cut back on the jet size. smaller jets equals less fuel. less fuel/air equals less hp. altitude makes no difference.

I confess I didn't read the entire article, but the part that caught my eye was the one I am discussed in my previous post.

[rhjames]

Correction:

altitude makes no difference except when running naturally aspirated engines.

higher altitude equals less oxygen per liter of volume. less oxygen, less power.

its that simple, as stated in my first post on this subject...

[T_MaX]

I have seen this argument before!

Trust me when I say, "Dyno Results are only as true as the operator wants them to be"!

A chassis dyno is a very good tool, but unless all tests are preformed under strict uniform conditions that include machine calibration as per the manual and a controlled atmosphere, the measurements taken should only be considered “Ball-Park figures”, IMHO.

[Herr-Kuhn]

RH....A turbo car will make slightly less power at altitude as compared to sea level...this is because the pressure ratio is higher when running the same boost at altitude. The turbo pumped up the same level, but it had to work harder to do so, thus higher PR and more heat from compression. It would not be near to the losses a NA car experiences under the same conditions though. This is why turbo cars are popular in high altitude areas, like Denver.

[Herr-Kuhn]

http://www.hi-tm.com/Documents/Calib-boil.html

Some information on barometric pressure changes as a function of altitude (all other factors equal)...

[Danglerb]

Carl's Pikes Peak thread has some good comments about turbo power at altitude.

Both of my turbo cars were a real pleasure to drive at higher altitudes, and all of my NA did some huffing and puffing.

[Red Baron]

Good reading, thx for sharing that.

[rhjames]

Herr---

it's because the air is thinner (less O2 as well), not that the barometric pressure is different (higher or lower).

t/s charged engines (at high altitude) work better because of the pressurization of the intake charge. N/A engines are the ones that suffer......


sorry, try again.....

[Mule]

So is there some difference of opinion as to whether lower atmospheric pressure results in thinner air?

[Danglerb]

Originally posted by Mule
So is there some difference of opinion as to whether lower atmospheric pressure results in thinner air?

Depends on the temperature.

[Mule]

And the rotational variance of the planet divided by the hyper-gauss of the Van Allen radiation belt minus the deterioration of the ozone layer as described by Al Gore.

[rhjames]

give it a rest mule....

your non-over simplification of what's going on is, well, just tiring.

if you really want to debate theory, that's fine. Go back to engineering school and get after it.

you and your teacher can have years and years of discussing why VE has anything to do with turbo charging, or the helmholtz theory and why the pressure differentials at the intake valve do or do not create pressure waves causing the intake to be pressurized.....etc.

The theory is OK, but you can't put a gauge on it and measure it at speed.

Helmholtz didn't put a gauge on it, neither did Larry Morgan or any other prostock racer you referred to....

it's just theory.

to use your argument, give me some factual numbers for your assertions and theories. then we'll talk.

until then, try again.

------

[rhjames]

the tables in the above referenced article are interesting, but my question is this?

why are they using different barometric pressures at each altitude, as opposed to the same barometric pressures across the board.

in other words:

at sea level the barometric pressure is say 29 in,

at 500 ft above sea level, again the barometric pressure is 29 in.

etc.

etc.

you will notice that the pressures are constantly changing as the altitude goes up, causing the boiling point to differ from the last.

So using that theory, if you kept the barometric pressures the same for each altitude, what would the expected change in boiling point temp be?

for all of you physics geeks, let's see where you go with this one.....

[Herr-Kuhn]

RH...The altitude plays a huge role in the air's density. It is a simple Pv=nRT relationship. Density is directly proportional to mass...Density=mass/volume. Barometric pressure does vary with altitude...this is precisely how an altimeter works. Yes, pressures do change...this is why you always set your altimeter when you are going you pre-flight inspection....the altimeter is then set to the pressure of that day and measures the pressure difference to give an altitude reading. Move into another pressuze zone due to variations in weather and re-calibrate your altimeter before you land to get an accurate altitude reading.

Here is a good article on the subject:

http://wahiduddin.net/calc/density_altitude.htm

[Mule]

Precisely Kuhn.

Rh, sorry if my attempt to further "articulate" the point didn't help you. Call one of your pro-stock buddies & explain to them that the air "runs in" when the valve opens (we just need faster air) and that if they believe the myth of port tuning they are idiots then get back with me.

[rhjames]

I wasn't going to prolong the death of this thread, but here it is.....

I've read the theories, run the same theories on the discussed intakes, ad nauseum.....

What isn't said here, or in the theory papers, is cold hard facts.

What also is not said, is that the engine vacuum overcomes and pressurization of the intake due to positive pressure waves.

Theories are fine. Sometimes they withstand the test of time.

Even Stephen Hawking's theories are now in serous question.

Your assertion about atmospheres relating to horsepower improvement (multiplication) was off, and I gave you the numbers to prove it.

Put an end to this non-sense, or open up your own research lab and publish a paper describing your theories and research for all of us to pick apart.

Until then, as jimmy123 said, its all talk.......

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