GlenL

The balloon goes backwards!

This is because it is lighter than the surrounding air. The air is being accelerated towards the rear (decellerated towards the front) and this causes a pressure gradient with higher pressure towards the windshield. The balloon, having less mass, gets forced to the rear by this.

What do I win?

ErnestSw

This thread is an enormous mental circle jerk!!

m21sniper

Quite simply, no one on earth knows. For that matter, there isn't even universal agreement in the scientific community on the big bang theory anymore.

So, the answer..........who knows?

Not us(and yes, that includes you too Mark, lol).

mark kibort

go back to my values post! i have the torque /hp to the wheels throught the gears at every shift point. this is not basic drag racing gearing. we are talking about a rear end change that exactly matches the gear spacing. cant you see this???? the ONLY benefit is the sub-1st gear, the rest of the gears are near identical. BUT the fact that they are not that identical in the final gear for a drag to 115mph in a 1/4mile, tells any D student in physics that there is lower hp applied (lower final gear ratio torque) to the finish line that counter acts the gains in the sub-1st gear. (of 12.5:1 vs the stock 1st of the 2.2 of 8.9:1)
dont you get the fact that all we want to do is maximize the hp to the wheels over the entire speed range.

its force x distance = work. OK???? HP is the rate of which work is done (how fast the car can accelerate) the fastest a 300hp engine could accelerate is if it would be applied to the wheels over the entire distance. (thats where gears come in) HP x Time is the energy used, or the Kilowatt hours used. Ive said HP seconds, which is a unit of work or energy, not HP (power.)

power = dWork/dtime = F ddistance/dtime = F x veolcity

in acceleration in drag racing,the acceleraton rate is going down, speed is going up and force is going down. ALL dictated by the HP applied to the rear wheels. at any speed, give me a hp number the the engine is running at and you can calculate torque at the wheels. maximize hp at the wheels at all speed ranges, you get the fastest acceleration.

Open your mind to the trade offs. the 3.09 is an EASY example of this. because its only a shift of the gears down a full ratio. the gears are not closer together . again, you gain 26% more torque/hp to the wheels up to 39mph and thats agreed right (not the 140% that the gear ratio change would indicate to guys like MSniper and 6.0) after that, there are a series of gear ratio trade offs vs HP available. iin the end, mathamatically, assmuming same driver skill, no traction variables, etc, the power to the wheels will be very similar to the end of that 1/4 mile drag..

what folks do with drag racers is what i would do if i went from 400hp to 600hp with a 928. id go to a rear end ratio that gave me max rpm at the finish line . (if i couldn't change the internal ratios of the gear box. ie made them closer) if i continued in hp, i would evntually go back to the original gear box as i would be fully using the next gear (ie going from 115mph at the finish would require a 2.2 box, going 155mph at the finish would also require a 2.2 box) anything in between could use a different final drive gear box. the 3.09 doesnt change anything. actually, its fine tuning and there would be a case for it to a top speed of 120mph vs 115mph.

thats just the physics of it. Please, look at the torque values. its pretty simple vs the time spent in those gears. it shows the torque/hp to the wheels over the gear shifts and gives the net power available to accelerate the mass (vehicle)

Mk

m21sniper

Hey, whatever it takes!

mark kibort

good answer Sniper! thats right.

Mk

mark kibort

No, glen has it right (Glen you were supposed to wait for all the non physics types to chime in) I always ask this question when interviewing new engineers

the balloon moves backward when you press on the brakes and moves forward when you punch it. MSniper, care to explain why, or do you doubt this.

think about it!

MK

m21sniper

"Refresher".........LOL, your arrogance knows no bounds.

I would be highly amused to watch you take your condescending tone to a man with more engineering experience than you will acrue in 10 lifetimes.

You can find him here: http://forum.a-10.org/

He posts under the screen name "Mr. Mudd". Feel free to run your "2.2 is as good for drag racing as 3.09" by him.

The fact is, unless there's another 928 there you couldn't even FIND a 2.2 car at any dragstrip. To a drag racer, anything under a 3.23 is a highway gear, and cause for immediate replacement, lol.

m21sniper

Glen already answered it.

Does that apply to helium balloons only(or i suppose hydrogen too, lol), or air filled ballons also?

mark kibort

Just stating facts.. Ive had this conversation with many engineers only to agree after they recall some of the basics here. its not as easy as it seems. many have forgotten much of the basics. I use this stuff in my work every single day. most do not.

you keep on talking about 2.2 this, and 3.09 that ,and 4.45,....... it doesnt matter what the final drive ratio. im sure i can make a 2.2 rear end with the exact same gears as anyone (barring mechanical size limitations) bottomline, if you fail to recognize the gear system is what you need to talk about and gear spacing, you miss the target by a long shot (and i thought you of all folks would want to hit the target!)

a lot of my teachers and coaches were arrogant, and god love them for standing their high ground in classroom arguments like this!! heck, i wouldnt have learned a thing if they werent! if arrogant means (i know something) then yes, about this topic, i am arrogant

MK

mark kibort

what do you think??? Glen, no help here.

(Im not asking to be condesending, im asking to make a point as it carries over to that entire acceleration discussion)

Mk

m21sniper

I think it would only apply to a balloon that was filled with a LTA gas.

A balloon filled with air should 'go forward', one with helium or hydrogen, backwards.

James-man

The balloon experiment proves nothing in the context of drag racing.

Generalizing here: what is key for drag racing is having the highest speed at the earliest portions of the track as all of the gains from there, as you work through the gears, are cumulative.

You are citing theories that are really groovy. But there are assumptions being made that probably offer significant variance. +/- 1/4 second? +/- 1/8 second? Either way, that is winning or losing a drag race.

If a set of drag racer dudes indicate that common knowledge is that XYZ rear end ALWAYS outperforms ZYX rear end, you just hafta wonder if there isn't empirical evidence of something that is meaningful. A true scientist would go back to theory and ask, hmmmm, what have I missed if theory doesn't fit observation?

The real question is, what is common knowledge in drag racing and why is it contradictory to theory?

I am afraid that theory has conveniently assumed away critical hard to measure components such as launch etc. that are so easily and readily bucketed as driver skill & consistency issues.

What has the world seen and have to say? After that is done, pull out the theoreticals to explain it.

James-man

Braking is not applicable in drag racing which is the context of this whole thread isn't it? If I recall, we are splitting hairs on what actually happens during upshifting. We know that you miss out on a fraction of a second of acceleration during an upshift. How much time it eats up on the 1/4 is an even smaller fraction of a second. I don't believe that a car loses much velocity on a shift until you start getting into double digit speeds. So in the context of stockish 928 drag racing, I still have to wonder if improved launch control offers greater benefit that the time lost having an extra shift.

m21sniper

"you keep on talking about 2.2 this, and 3.09 that ,and 4.45,....... it doesnt matter what the final drive ratio. im sure i can make a 2.2 rear end with the exact same gears as anyone (barring mechanical size limitations) bottomline, if you fail to recognize the gear system is what you need to talk about and gear spacing, you miss the target by a long shot (and i thought you of all folks would want to hit the target!)"

We have already stated that our transmission gears were constant for the purposes of this discussion, all that's changing is the ring and pinion.

I'm sure you COULD make a 2.2 ring and pinion behave as an otherwise identical car witha 3.09 IF you changed the transmission gears to mimic the ratios of the 3.09 box..........BUT WE'RE NOT DOING THAT HERE!

The fact is that the 3.09 car being discussed here will have a mechanical advantadge of 26%(59 effective HP) until 39mph(all your figures).

In that time the 3.09 car- with equal traction- will open approxomately a 2 car lead(about .2 seconds). The whole rest of the race the 2.2 car will be trying to make up those 2 car lengths, but be doing it against a car that from 2d gear on is identically geared.

IOW, it ain't happening.

The only time the 2.2 car will have any advantadge at all is during the extra shift the 3.09 car will have to make, but assuming an A/T, you are talking no more than a few hundreths of a second- far less than what would be required to make up for the advantadge the 3.09 car gained at the launch.

Compare them side by side, the 3.09 car opens it's two car lead by 37mph(again your figure), then shifts into it's second- or the 2.2 cars first.

The 2.2 car is still in first, so there is no gearing advantadge for either car. At the exact same speed the 2.2 car shifts to second the 3.09 car will **** to third, and both will have the exact same gearing. Since the 3.09 car's third is the same as the 2.2 car's second, again, the 2.2 car will have no gearing advantadge....and will make up no lost ground.

Finally, the 3.09 car will shift to fourth at the exact same speed as the 2.2 car shifts to third, and both will be operating at the exact same gearing rate, so again, the 2.2 car will hold no gearing advantadge, and will not be able to overtake the 3.09 car.

The 3.09 car will cross the traps at around redline in 4th, the 2.2 car at about redline in 3d, with the 3.09 car approx. 2 lengths ahead.

We could do it 1000 times in a row, and given equal traction, state of tune, shift speed, and R/T, the 3.09 car would win every time.