If what you say is correct, there is an error in my previous math. Where is it? Knowing HP without knowing the weight of the car does you no good. When should I expect delivery? God I hope its not black.................... But you did not answer why the car V and car F accelerate at different rates even though they have the same HP; invalidating your claim.
It is you who are confused. But it looks more and more like you are EFWUN, are you? Are you capable of reading? Are you capable of cliking of the old thread "tell me about driving around at high RPMs" and reading it, and actually getting to the conclusion? And then understanding? No, probably not. Sigh!
Ive been on quite a few car boards, and I think every time this topic has come up, the same conclusion was reached! If you have to ask what the conclusion is, well, you just answered your own question!
An object does not need any more energy to accelrate from 200-220mph then from 0 to 20mph. If there is no frictional losses it takes the same energy. When an astronaught is sitting in his space ship moving at 18,000 miles per hour (which is quite a bit of kinetic energy) it doesn't take him any more effort to throw a banana to one of his comaraddes then it does here on earth. If what you said was true it would be many times harder to accelerate the banana in space then on earth. THe same can be said for the flight attending pushing a 200lb cart down an airplane isle. It doesn't take her any more effort to accelerate the cart at a dead stop then it does cruising at 500 knots. Now hp = (tq * rpm) /5252 There is no exception this how hp is calculated. THat is why on every dyno torque and horsepower are exactly the same at 5252rpm. Torque is what accelerates the vehicle not hp. HP is simply a made up way to interpolate how much potential work the engine can make when the torque is multipled by the transmision. You see peak acceleration is always at peak torque for any given gear. This is fact there is no iffs ands or butts . The only slight curve ball in this is if the peak torque happens late in the power band in an environment with friction increases with speed. Since the vehicle is traveling at a higher speed at the end of the powerband it faces more air drag restriction which means it takes even more torque to accelerate the vehicle so in other words if you had an engine with a flat 400ft/lbs from 2000 to 8000rpm you will see the acceleration fall off as the vehicle builds speed due to the increased force of air friction. Anyway air friction aside we can talk about 1st or 2nd gear where air friction is not very substantial. In those gears you will definately feel the most throw back acceleration force on you during the peak torque of the power band. What you feel is the torque curve not the horsepower curve. Now here is the deal where most people get confused. lets say we have two made up engines. Both engines make 300ft/lbs of torque and both make it tottaly flat from idle on. However engine A blows apart after 3000rpm so it only has a 3000rpm redline but the other engine (Engine B) can sustain that torque to 11,000rpm redline. WHen we plug the formula we find that engine A only makes 171hp while engine B makes 628hp. Now we will take both engines and stick them into a umm Modena lets say with identicals transmision. Now remember all that a transmision is is a torque multiplier. That is its function it sacrafices shaft speed in order to increase torque. So we put Engine A and B in the modena and take it to the drag strip. We'll pretend we have the worlds stickiest tires (never slip) and that both cars launch identical. Lets say that engine A will top out 1st gear at 15mph and since the gear ratio is the same engine B will top it out at 55mph. Both cars will accelerate with exactly the same rate and concequently the same g-force throw back up to 15mph. Both the 600hp engine and the 170hp engine will both throw you back just the same in the modenas first gear. This is a mathamatical certainty as the torque curves (or in our case a flat line) are identical. Now both cars are going 15mph and got there at the same time however now comes the kicker we are out of Rev's to convert to higher rear wheel torque in Engine A we have to shift to a higher gear. Upon shifting to 2nd gear we are increasing the engines torque to the wheels less then we were in 1st gear. Our Modena with Engine A is now accelerating slower from 15mph on then Modena B. Lets say Modena Engine A tops out 2nd gear at 30mph we have to shift again and again we are going to a gear with even less torque multiplication then the previous gear. So now in 3rd gear it is accelerating even slower (not to mention that air drag is building). So lets take the Modena A to the top of 3rd gear lets say top of 3rd gear comes at 50mph. Well Modena A now has to shift to 4th which lets say is a 1:1 ratio so now there is only 300ft/lbs of torque available to accelerate the modena from 50mph. Well when Modena B crossed the 50mph mark it was still in 1st gear and it was still putting down 3000ft/lbs of rwtq or whatever since it had the revs to stay in the lower gear for much longer. Thus it sustained a higher acceleration for longer thanks to how wide the powerband is. Ultimately in a drag race the 600hp MOdena B will obviously woop Modena A because it will stay in the lower gears for much much longer. Again both engines are capable of producing the same amount of instantaneous power but since engine B can sustain the power for much longer it can perform much more work. Hence we have found a way to describe this extra work that engine B can do and we called it Horsepower. I hope this brings some clarification to this post.
Yes I think it would, but gee, I really hope that I am too old to drive (and happy about that ...) before I have to buy and drive a CVT car. I cannot but imagine how boring it would be. Pete
My next observation is this..... If any given engine will provide the fastest acceleration at the torque peak, then why does every CVT transmission hold revs at the power peak during acceleration and not at the torque peak?
PSK, I think with the F1 trans already widely accepted and now the new "Zero Shift" coming into play we are rapidly moving toward that scenario. Maintaning rpm at or near peak horsepower is the goal and that's the way things are heading. Less driver involvement. I remember over twenty years ago Gilles Villenueve saying he wished F1 cars had front engines and skinny tires so he could have more fun using his inherent skills rather than the machinery and tires to kick peoples a%^es. What would he say about auto-shifting and traction control?
teak360, Okay I need clarification on this challenge, ie: This to me reads you want to see the calculated maximum acceleration figure a Ferrari Modena can ever attain, just using Torque and NO power figures. Answer: Thus the maximum acceleration will occur in 1st gear thanks to the maximum torque multiplication, thus: Specs from Ferrari for F360 Modena: Max Tq - 275.0 ft lbs (note I have excluded what rpm it is generated at ... because I do not care). Rear Tyres - 275/40 ZR 18 (thus approx 670mm dia.) Weight - 1390 kg (= 3064.43 lbs) Ratio for 1st 3.29:1 including diff (4.44:1) = 14.6076:1 overall. Thus at peek torque we have 275 ft lbs x 14.6076 = 4017.1 ft lbs at the rear wheels. Thus the force applied by the wheel is = 4017.1/1.11 = 3616.1 lbs to the road via the wheel. Thus as we are in first gear, air and rolling resistence will be negligible, thus acceleration will be = 3616.1 / 3064.43 = 1.18 ft/s^2 It will never be higher due to the fact that peak torque produces the most force at the rear wheels and any higher gears have LESS torque multiplication. Thus I have calculated a Ferrari 360 Modena's peak acceleration figure using Ferraris figures for Torque, weight and 1st gear and diff ratios. I have not used power anyway. I'd retract your challenge if I was you ... as a physicist is only going to do it better than me, or prove that I am close enough to be right. Pete
Who says they do? ... other than teak360 (and EFWUN). I believe that they will hold revs at peak torque if they are a genuine CVT transmission. Z06Kal analysis is a very good one and shows very clearly that torque rules in peak acceleration games ... but to maintain the acceleration you need revs. A CVT does not need to continue to rev higher as it can constantly change up, er, move up ... Pete
Okay I am not aware that Audi have created a REAL CVT?. I do know that they have the 2 clutch thingy with toggle changes. I will have to ask my Mother who works for an Audi service dealership. The 2 clutch thingy is NOT a CVT. Please point me to something that indicates that Audi has created a REAL CVT. Pete EDIT: Just went to www.audi.com and had a look to see if they have produced a CVT yet. Unless their own internet site is behind the times, Audi have NOT produces a CVT yet, instead they have produced the DSG direct-shift gearbox: Thus this gearbox STILL HAS GEARS and thus as we have already explained until my fingers have gone numb. If you have gears you rev passed peak torque so that when you change up the next gear is at or above peak torque to maximise overall acceleration. Thus a REAL CVT will sit at peak torque, not peak HP. Incorrect statement ... ... as it is a computer controlled NORMAL gearbox, not a CVT.
The units ft/s^2 should be Gs. The weight of the car is 3064 pounds for every 1 Gs of gravitational acceleration or 3064 lb/Gs. Now that we are in the right units; = 3616.1 lb / ( 3064 lb/Gs ) = 1.18 Gs Which is right at the limit of the best streetable tires today.
Thanks Mitch. I was confused what to do with the lbs in converting to mass. With kgs I usually times by 9.81G ... but I do not know what to do with lbs. Pete
Lets explain a REAL CVT because I think it is required. A REAL CVT will maintain constant engine rpm whatever the vehicles road speed. Naturally for peak acceleration you need to sit the engine at the rpm that results in peak force at the tyres. With a REAL CVT you would be ideal acceleration as it would maintain the engine at peak torque ... but how boring, the engine would just sit there at x rpm humming away!!! I believe DAF created a REAL CVT transmission many years ago using a special belt running in cone shaped pulleys that moved to change the working radius. Pete
one of the very important reasons why I am a big fan of Ferrari is because of the Ferrari's high-rev engines and the sound it produces. The high-rev ability of its engine is what distinguishes Ferraris from the rest. Nowadays, even a NSX or Civic Type R can rev up to 8000rpm. Torque is no doubt important but I wouldn't not want to improve the torque at the expense of rpm on a Ferrari.
Ok, I dredged up my old HP versus TQ data. I present two graphs at this time. Both graphs have one axis as speed and one axis of thrust; transmission, differential and tire rolling radius has been included; transmissioin losses have not been included, nor has air resistance. The first graph has the thrust profile of the F355, the second that of a non Z06 C5. To both graphs I added a line where acceleration is constant at the max power of that engine. This line has the shape of 1/V and a scale that puts it at max engine HP at all points in time like a CVT could. The vette is faster because the thrust profile through the gears is closer to the line of max HP that the stair stepped F355 profile. This is the argument of the area under the curve.Judge for yourself:
Gilera's parent company Piaggio have been rumoured to be developing the biggest scooter to date by marrying together their existing 850cc, 90 degree v-twin bike engine and a Suzuki Burgman type CVT automatic gearbox. Getting back to that gearbox, Gilera has been rather coy about exactly what technology they're using, and in his presentation, Lucio Masut, director of R&D, mentioned a full-CVT automatic mode. CVT (Continuously Variable Transmission) provides, as the name implies, an infinite number of ratios, often through belts and cone shaped pulleys, to perfectly match the engine speed to the throttle position, bike speed, etc. In theory, to get maximum performance, you just have to hold the throttle all the way open and the engine revs to the........ exact point of maximum power and stays there while the CVT runs through its infinite ratios. No pauses for manual gear changes, just continuous maximum power to the rear wheel. In practice, problems with torque capacity and internal inefficiencies mean CVT systems have so far been unable to match the performance of manual gearboxes. It looks as if we'll have to wait to see exactly what they have up their sleeve for the Gilera Ferro
Okay I have done a little bit more investigation and I have found reference on the net that Audi do indeed offer a REAL CVT transmission (strange that this is not mentioned on their own site). This CVT is by a belt/chain method so no gears. My reference: http://www.ebroadcast.com.au/ecars/A.hints/CVT.html I also found this comment (from same site) about torque interesting: Not how this statement clearly infers that TORQUE pushes a vehicle along and how above maximum-torque the car will SLOW down ... and as the car slows towards peak torque it will speed up ... Pete
Why did you leave this part out of the same article? On the same page no less: "Maximum acceleration at a given speed is attained by having the engine operating at maximum power." You also left this out, on the same page again!: "So, if you are into racing, particularly Formula One racing, you want an engine with the highest possible power output" You notice they didn't say "torque output".
Because we have already discussed that ... remember F1 cars have gears, and there are huge advantages in being able to hold that gear to much higher rpm. To be able to do this the engine must produce good power, ie. continue to be able to generate good torque as the rpm rises. Glad to see you CAN read Pete
And this sentance shows exactly why a big TQ engine is easier to drive around town. As the vehicle slows down the available TQ increases, whereas the small TQ Ferrari engine has the property that as the vehicle slows down the available TQ remains rather constant. [QOUTE=teak360] Why did you leave this part out of the same article? On the same page no less: "Maximum acceleration at a given speed is attained by having the engine operating at maximum power."[/QUOTE] This statement is true for CVT drivelines and not true for gear driven transmsiions. Since the cars we are talking about are the later, the sentance is not relevent to the discussion at hand.
