question

[Ankf00]

combustion homework right...

problem statement involving rahal's '87 Cosworth DFX, the statement says 48" mercury gage boost pressure, is that correct? I thought CART pressures were measured absolute.

correcting the hillbilly's not quite finished book earns me pts which I need, so I ask

thanks.

(at least the prof's got extraneous info like chassis and cosworth DFX history in there, so he gets some cool points)

[gjc2]

As far as I remember they always expressed boost pressure in inches of mercury.

George

[pfc_m_drake]

combustion homework right...

problem statement involving rahal's '87 Cosworth DFX, the statement says 48" mercury gage boost pressure, is that correct? I thought CART pressures were measured absolute.

correcting the hillbilly's not quite finished book earns me pts which I need, so I ask

thanks.

(at least the prof's got extraneous info like chassis and cosworth DFX history in there, so he gets some cool points)
I believe you are correct - inches of mercury absolute.

[Madmaxfan2]

Warning, Madmaxfan2 is a degreed Mechanical Engineer, so I actually have some knowledge of fluid dynamics ( yes, air is technically a fluid ). Absolute pressure is the total amount of pressure available with a complete vacuum being 0 inches of whatever pressure as the reference. The earth's atmosphere have an absolute pressure of 14.7 psi at sea level. Most common pressure measurement instruments can only measure the added pressure of whatever mechanical device produces ( in this case a turbocharger). Therfore, any boost pressure limitation is only technically correct when stated in gage pressure ( the difference between total absolute pressure and available atmospheric pressure). Atmospheric pressure is variable with elevation and weather being the major factors. Yes, totol available pressure is a major factor in engine output, that is why cool dense weather is good for engine HP and places like Dever sap engine power output. The rules are the same for turbocharged engines, it's just that high boost engines produce so much added pressure that atmospheric effects become neglible. In summary, absolute pressure is an uncontrolable, but gage pressure ( the added pressure by a mechanical device) is controlable and therfore can be regulated. Hope you still are awake here. :)

[pfc_m_drake]

Madmaxfan2:

That's great, but you missed the entire point.

The question is the following; was the boost limit on the '87 Cosworth DXF:

1) 48 inHg gage = 77.9295 inHg absolute OR
2) 48 inHg absolute = 18.0705 inHg gage

(both assuming 14.7psi atmospheric)

And I'm pretty sure that the correct answer is #2.

Edit: And one of the reasons I say that is because I'm pretty sure if you look at the current CART rules (and I have no way of checking them at the moment) but they specify the boost limit in inHG absolute.

[Wolverine]

And one of the reasons I say that is because I'm pretty sure if you look at the current CART rules (and I have no way of checking them at the moment) but they specify the boost limit in inHG absolute.

You are correct. In fact, paragraph 9.5.4A.1 of the 2004 Champ Car rule book reads as follows:

"The allowable intake manifold pressure shall be limited to a maximum pressure of forty-one and a half (41.5) inches of mercury absolute [emphasis added] for road and street course events for the 2004 season. The allowable intake manifold pressure shall be limited to a maximum pressure of thirty-nine (39) inches of mercury absolute for oval events for the 2004 season."

[Ankf00]

sweetness.

thanks all!

[Wheel-Nut]

combustion homework right...

. . . . .

correcting the hillbilly's not quite finished book earns me pts which I need, so I ask

. . . . .


Beats mowing his lawn or dating his ugly daughter!

[JLMannin]

Folks,

p.s.i. and inches of Hg are not the same!!!!!

Yes, sea level pressure is 14.7 psi (that's pounds per square inch). Inches of Hg is measured with a manometer. A mercury manometer is basically an evacuated clodes-end tube immersed in a pool of mercury (over-simplification). Atmospeheric pressure pushes the mercury up into the tube, counter-balancing the force of gravity. At STP (standard temperature and pressure, ie, sea level, 273 Kelvin), the column of mercury will be 760 mm tall. The unit of mm of Hg is defined as a torr, by the way. Converting to inches, this comes out to 29.92 inches.

The meterological term for a mercury manometer is a barometer.

Since the pressures stated in the rules are absolute, the pop-off valves need to be adjusted each day according to what the barometric pressure is. This is how Foyt was always able to pick up 4 mph on pole day every year.

[Nosuchsoul]

You guys are cool.

[RichK]

Folks,

...manometer.


Isn't that a Muppets song? (http://www.poppyfields.net/poppy/mahna.html) :)

[Madmaxfan2]

So, if absolute is the standard, the boost limiter would have to be readjusted every day. Anybody close to the techincal inspection processes used by CART can confirm the above stated assumptions in this thread ?

[rosawendel]

is that using with the flux capacitor, or the dylithium crystals? :laugh:

[pchall]

Slightly off topic:

When did Americans start regularly spelling "gauge" as "gage"?

I've got a note for this mispelling in Autoweek in 1994 and a reply from the writer that he always spelled it that way.

If we get enough evidence we can get the members of Off Camber recognized as contributors to some future edition of the Oxford English Dictionary for recognizing a shift from British to American spelling.

Not that it would be worth anything except for bragging rights at bars where English professors hang out.

:p

[Turn7]

PCH...funny you bought that up. I was doing a spell check the other day and it wanted to change gauge to gage. I said :confused: WTF? I had to go to my old dictionary to make sure I wasn't going el loco.

[pinniped]

so MadmaxFan2, are you saying that the effects on a turbocharged engine are just as great as they are for a normally aspirated one? I'm not saying that is wrong - just that what one continuously reads in automotive magazines is that the turbo negates that by simply packing air (ahem, fluid) into the combustion chamber until the same pressure is acheived...so it really does have the same affect, but just that the affect is less noticeable with a high pressure system like a turbo engine as compared to normally aspirated? (hopefully question makes sense)

[Nosuchsoul]

Since a gas is also a fluid. Does that mean when you Fart you can always say you let loose a wet one?

Thank you folks, I'll be here all week. Please remember to tip your waitress!

[Turn7]

Ok, Here is another kink in this that may or may not be relevant since I am not any sort of mechanical guru.

If they are measuring the pressure inside of the intake manifold, how much variance is there from the 14.7 psi, since an intake manifold on a normally aspirated motor is under vaccum? Preceivably it would be a lower reading than what is measured outside of the intake.

[RARules]

Hey, this sounds really simple to me. ;)

OK, it's absolute pressure, that is, compared to a vacuum. So that implies several things:

The pop-off valve measures relative pressure, and therefore should be recalibrated for each venue, and perhaps for changes in weather. Of course, even an error in this pressure still provides the same absolute pressure for all cars (although it's possible to design things between manufacturers to make the difference in absolute pressure make a relative difference in performance between manufacturers' engines - remember spacergate?). This is a secondary or tertiary effect, though. Therefore:
The absolute manifold pressure is the same in Denver as it is in Miami.
The amount of charge that is injected into the cylinder (all other things being equal) will also be equal.
This should really make the altitude difference irrelevant from an engine performance standpoint (still not so for wing adjustments, of course!).

[JT265]

Hey, this sounds really simple to me. ;)

OK, it's absolute pressure, that is, compared to a vacuum. So that implies several things:

The pop-off valve measures relative pressure, and therefore should be recalibrated for each venue, and perhaps for changes in weather. Of course, even an error in this pressure still provides the same absolute pressure for all cars (although it's possible to design things between manufacturers to make the difference in absolute pressure make a relative difference in performance between manufacturers' engines - remember spacergate?). This is a secondary or tertiary effect, though. Therefore:
The absolute manifold pressure is the same in Denver as it is in Miami.
The amount of charge that is injected into the cylinder (all other things being equal) will also be equal.
This should really make the altitude difference irrelevant from an engine performance standpoint (still not so for wing adjustments, of course!).



Good points.

BUT!

Would this not have an adverse effect on the space/time continuem?


:D

[lone_groover]

Have you guys taken the heat of the meat into account?

:gomer:

[RARules]

Hey, where's Obi-Wan?...

[Robstar]

Good points.

BUT!

Would this not have an adverse effect on the space/time continuem?


:D

& do we need any modifications to the flux capacitor ?

[RTKar]

Warning, Madmaxfan2 is a degreed Mechanical Engineer, so I actually have some knowledge of fluid dynamics ( yes, air is technically a fluid ). Absolute pressure is the total amount of pressure available with a complete vacuum being 0 inches of whatever pressure as the reference. The earth's atmosphere have an absolute pressure of 14.7 psi at sea level. Most common pressure measurement instruments can only measure the added pressure of whatever mechanical device produces ( in this case a turbocharger). Therfore, any boost pressure limitation is only technically correct when stated in gage pressure ( the difference between total absolute pressure and available atmospheric pressure). Atmospheric pressure is variable with elevation and weather being the major factors. Yes, totol available pressure is a major factor in engine output, that is why cool dense weather is good for engine HP and places like Dever sap engine power output. The rules are the same for turbocharged engines, it's just that high boost engines produce so much added pressure that atmospheric effects become neglible. In summary, absolute pressure is an uncontrolable, but gage pressure ( the added pressure by a mechanical device) is controlable and therfore can be regulated. Hope you still are awake here. :)

Maybe that's why the gomers didn't like pop-off valves....they weren't smart enough to understand them...

[nz_climber]

Hey, this sounds really simple to me. ;)
This should really make the altitude difference irrelevant from an engine performance standpoint (still not so for wing adjustments, of course!).
[/list]

There is less oxygen at the higher attitude - hence less performance (the pressure could be the same but the oxygen ratio in the air would be less?)

Correct me if im wrong?

[lone_groover]

Good point 'climber. But you also need to factor-in the angle of the dangle.

:)

[nz_climber]

Good point 'climber. But you also need to factor-in the angle of the dangle.

:)

o yeah forgot to add every thing should be multiplied by 42 (being the current meaning of life ) :D

[RARules]

o yeah forgot to add every thing should be multiplied by 42 (being the current meaning of life ) :D

But what's the question? ;)

Seriously, I once met Douglas Adams (RIP...) in person at a conference and asked him why he chose the number 42, and whether it had any special meaning to him.

Of course, he indicated that it was a totally random choice - no meaning at all.

[Ankf00]

Slightly off topic:

When did Americans start regularly spelling "gauge" as "gage"?

I've got a note for this mispelling in Autoweek in 1994 and a reply from the writer that he always spelled it that way.

If we get enough evidence we can get the members of Off Camber recognized as contributors to some future edition of the Oxford English Dictionary for recognizing a shift from British to American spelling.

Not that it would be worth anything except for bragging rights at bars where English professors hang out.

:p

not that I'm not all for bagging rights w/ the English professors ;)

but gauge I understand to mean a size or a method of measurement or a measuring device itself or to measure something

gage I understand to mean pressure relative to atmospheric pressure only

[Ankf00]

Ok, Here is another kink in this that may or may not be relevant since I am not any sort of mechanical guru.

If they are measuring the pressure inside of the intake manifold, how much variance is there from the 14.7 psi, since an intake manifold on a normally aspirated motor is under vaccum? Preceivably it would be a lower reading than what is measured outside of the intake.

manifold air pressures can drop to as low as 4.7 psi when the throttle's closed, and as you open the throttle gradually increasing the engine load all the way to wide open throttle, you get closer and closer to atmospheric pressure at 14.7 psi

[JLMannin]

There is less oxygen at the higher attitude - hence less performance (the pressure could be the same but the oxygen ratio in the air would be less?)

Correct me if im wrong?

The composituion of the atmosphere (in the trophosphere, anyway) does not change. The ambient pressure decreases with altitude, as the air is less dense; but that less dense air has the same composition as more dense sea level air. Yes, there is less oxygen per unit volume, but there is less nitrogen (and all other gases) per unit volume as well.

[nz_climber]

The composituion of the atmosphere (in the trophosphere, anyway) does not change. The ambient pressure decreases with altitude, as the air is less dense; but that less dense air has the same composition as more dense sea level air. Yes, there is less oxygen per unit volume, but there is less nitrogen (and all other gases) per unit volume as well.

Ok thanks for that, I knew it sounded to simple for me to understand ;)

[pinniped]

But wait, does this mean that one is to fart at high altitude, that the fart molecules would be further apart than at sea level? And if so, does that not mean that the fart smell would be less concentrated around "ground zero". Please advise, I'm going skiing this weekend.

[Turn7]

Theoretically yes. However, being that you will be going from to a higher atmosphere, the pressure inside your body must equalize by increasing the expulsion of pressure. Therefore, what you lack in concentration, you'll make up for in volume.

[pinniped]

Will this have any affect on the pounds of thrust available?

[Robstar]

Depends where you're going skiing... ;)

[Madmaxfan2]

RARULES is correct. The biggest factor in engine HP is airflow. An naturally aspirated engine does product a vaccum as compared to atmosperic pressure. The pistons moving provide a pumping action, therefore "pumping loss" describes the paristic effect of drawing in the air. Turbos negate this loss. You can bet the top F1 engines have as little pumping loss as possible.
"turbogate" was all about how Honda and Ford used creative engineering to tap the low static pressure region of the plenum to get more boost. Toyota bitched about this and we all know what happened. This incident proved that Kirk Russell was not only a bad cheif steward, but also a marginal chief technical inspector, since he aprove all the plenum designs and where the pressure taps were located. Lee Dystra was an excellent choice for his replacement and had he been in charge all along, maybe Honda would have stayed.I guess we will never know. I doubt the Brain Barnhart is smart than Russell, and a former incarnation of IMSA also suffered badly due to a bad technical call.

[TravelGal]

I can't believe I read the whole thing. (so far) :rolleyes: