mark kibort

Classic, that you are still able to find errors in spelling, but never in the logic here. CLASSIC!!

mk

Veloce Raptor

That isn't spelling, my gladiator-loving friend.

That is basic grammar that most of us learned in the third grade.

Way to demolish the remains of yoru credibility!







Professional Racing and Driving Coach

mark kibort

I think we (most) all understand acceleration being the 1st derivative of velocity and the second of distance. thats not the argument. you want to understand acceleration of two vehicles over a speed range, we can talk in hp-seconds or ft-lb-seconds. integeration of the HP or torque curves wont do it, as there is different times spent at the end or the beginning of each gear shift.

power is the rate of change of kinetic energy. regardless of engine torque numbers. Just go back and look at the curves I posted. I think its pretty clear which one will generate more F at the rear tires at ANY vehicle speed!

The only way a lower torque engine would cause any less acceleration at ANY vehicle speed, is if it had less HP available at that moment. If it did then it would not generate the same torque at the rear tires. This is the ONLY way that a lower torque engine can acceleratate less than a higher torque engine at any vehicle speed.

I find it amazing that im quoting a law of physics and there is even a debate. I understand curiosity to understand it better to fit any circumstance, but to call it wrong, is really silly.

Acceleration= power/(mass x velocity) Or, Acceleration = power/ momentium

Its the law! not my law, newton's .

15 years at making my living at this stuff says its true!

mk

mark kibort

Kettle????

By the way it may look like grammar to you , but
"you're" missing a 'e is typing like that little cute manic typing cartoon you posted. Oh look, you did the same thing.

"remains of credability". Hmmm, no attacking on your side. Also, NO ONE has challenged the facts Ive posted.
Its always amazing to me how those who dont get it, or dont want to learn, always try to derail a discussion to live in "ignorance is bliss" mode.

Also, a famous saying comes to mind. and please correct me if Im wrong here. go to your local college, give ANY of my posts, descriptions, graphs, equations to a physics instructor, or someone knowledgable, and see what they say. The saying is: "People always mock what they dont understand. Hmmm , sound familiar?"

mk

Veloce Raptor

it was a JOKE, Mark.

By the way, I am not familiar with the word "creditability". Please explain. Use at least 400 words.







Professional Racing and Driving Coach

sjfehr

OK, this is easy enough to prove; this data is readily available. Let's assume an 09 C4S, 385hp, 3400lbs. (287kW, 1542kg). I think we're all familiar with cars in this general performance category Let's ignore torque, ignore drag (only a small factor at these speeds with this car) and simply compute by kinetic energy:


HP*t=Ek=1/2mv^2

By HP and mass:
0-30mph (13.4m/s) in 0.48 seconds
0-45mph (20.1 m/s) in 1.1 seconds
0-60mph (26.8m/s) in 1.92 seconds
0-75mph (33.5m/s) in 3.0 seconds
0-110mph (49.1m/s) in 6.47 seconds
[Half the hp @ 192hp = twice the time to each speed.]

Actual (manual transmission):
0 - 30 (sec): 1.5
0 - 45 (sec): 2.8
0 - 60 (sec): 4.2
0 - 75 (sec): 6.2
1/4 Mile (sec @ mph): 12.5 @ 110.9



Now, I used engine horsepower which I know is wrong; I didn't expect to have to literally half that HP to the wheels to get the plots to match, though! In the end, though, I think I proved myself wrong. I was expecting to see the actual acceleration as the near-arrow-straight line to around 120mph that I recall from my owners manual, while knowing that the actual Ek chart is parabolic. I'm enough of a scientist to admit when the data has disproved my hypothesis, though. You're right; the data matches a pure and simple kinetic energy plot. It also shows that the C4S was considerably slower to 30mph than the numbers would otherwise indicate, which is, I imagine, a direct result of poor gear ratio when starting from a stop.

Not when both engines are running the same gearing at 4000rpm they won't! Which was my point. Unfortunately, it doesn't really add anything to the debate since HP are drastically different between the two engines in this example, so I'll let this one lie.

2BWise

I'm going to give one more try, but to do so this is going to be long so that I can attempt to cover one entire long thought. Bare with me.

F=ma -> At the rear wheels the largest force at the contact patch will provide the greatest acceleration. It is a function of the torque and rolling radius. If we assume the same rolling radius, the vehicle with the larger rear wheel torque will produce the greater force. Note that this is rear wheel torque and is directly proportional to the engine torque and the overall gear reduction. Therefore, for two different vehicles to produce the same rear wheel torque at the same vehicle speed the engine torque, gear reduction, RPM, and rolling radius have to be manipulated for a theoretical comparison to be valid and there are a lot of iterations plausible.

So as we exit a corner if we consider the vehicle at constant throttle, i.e. steady state, at the instant we attempt to add throttle the force at the contact patch is defined and the one with the greater force at this moment will accelerate off the corner quicker. Now, this will only continue down the next straight if that vehicle continues to produce the greater force the entire straight. It is now that we have to either keep up the torque or increase the revs. This is horsepower the measure of work over a period of time.

To do this we can do one of two things. High torque, low rpm or low torque high rpm. For a high engine torque, lower RPM motor we have a gear ratio of X (this is final reduction including primary, gearbox, final), now for a low engine torque, high rpm motor, we will need a gear ratio of >X to get the same rear wheel torque. Here will see a lot of compromises because to A)keep the vehicle in the power band and B)reach reasonable vehicle speeds. This is where this discussion has really been thin. Gearbox optimization for the low rpm vs high rpm motor will be sustaintially different. The low rpm motor needs ratio X, the high rpm >X, and therefore the low rpm motor to see the same vehicle speed with see a smaller torque multiplication through the gearbox where the high rpm motor for the same vehicle speed will end up with a larger torque multiplication.

When it comes to the design standpoint the goals should be to have
A) the largest possible torque near the lower end of the used rpm band. We gear the car properly as to maximize our torque output at this point to maximize the acceleration off the corner as well as to maximize our area under the TQ curve.
B) to keep that torque nearly as high for the entirety until the shift point (redline), to maximize HP thru the usable rev range to get us down the straight
C)the range of B needs to be in a range so that we have the maximum area under the curve. If we assume the same operating rpm range then maximizing the area under the HP curve means maximizing the area curve the TQ curve.

The above links design of two major components the engine and drivetrain. Now most companies are going to design the engine first and driveline second since it is easier to optimize the driveline to fit the engine's characteristics than the converse. This is why this theoretical case is hard to conceptualize. You take two vehicles making similar numbers and ask which would I prefer the one with the higher HP or TQ. There is not going to be any defined rule which is better since from a dyno curve only we can't make a truly informed decision. We get a picture of the overall performance. If we then look up the gear ratios and calculate out torque vs vehicle speed and vehicle speed vs rpm we can finally get a clue as to which will be better off the corner and which will be better down the straight.

Thanks for baring with me through that and I don't think I screwed up my thoughts too bad. Please note that my standpoint is as follows; The engine is defined, but we have the possibility to move the peaks/area by defining the ancilleries. Once these are defined the rev range can be nailed down and the driveline can be designed to match. And because these threads are always better with pics.

Enjoy

mark kibort

Great, Im glad you got it. You had me going there for a second when I was trying to figure out the graphs. AND where did you come up with those equations?? Really!!?

as far as your last sentence, its part of the issue I have with many others in this type of discussion, until they find out what you obviously know, that when you use one gear and the same rpms, you get ironious results, due to the fact that the HP at any speed now is very different, which is the entire point of the discussion.

remember as far as kinetic energy goes. If we didnt have air resistance and friction, i could get a 3400lb car to 60mph eventually, with only 1 hp.

rate of change of kinetic energy is the key. it equals power! Its how rolling dynos work for the most part.

mk

mark kibort

you start out right and then get into area under the torque curve, which is never the case. You need to maximize time spent in the highest values of the HP curve possible. Its not really area under the HP curve, its at least an average, and at best HP-seconds. (time spent at the highest HP levels posible) this maximizes the rear end torque found after gear multiplication at the wheels and thus force to the ground.

as far as the set up of the problem is concerned, my graph for Dez's hypotetical car with equal HP yet different torque, can yeild the same, greater or less rear wheel torque. The graph posted is one possibility. the shape of the hp curve will dictate what is found at the rear wheels for a same peak HP engine comparison. (with greatly different engine torque values). You talk about the car with the greatest force at the rear wheels applied over a straight, curve, etc, will accelerate the fastest and this is exactly right. This is determined by HP not engine numerical torque values as you speak to in the beginning of your post.

Now, you end up off a little saying that you cant determine acceleration due to gearing, etc, with regards to knowing the hp. this is not true. a hp curve will absolutely determine the torque at the rear wheels at any speed. remember we are talking about same car with proportionally different final gear ratios. (same difference in the rear end or final gear ratio, as the redline of the two engines) Gear spacing is assumed to be the same. this is an easy one, as most street sport cars have a 27% RPM drop per shift, and even if there is a variance there, its not that much of a factor unless we are talking close ratio gear boxes.

For example, Ironically enough, my car has a very broad HP curve. this means in racing, i almost have the effects of an infinitely variable gear box, because I always have at least 350rwhp to the rear tires at any racing acceleration speed. a peakier HP engine, might even have more HP , but less average HP or (hp seconds) and will have less force to the wheels in the lower RPM areas. Hence the point of VRs preference of high torque engines. usually, that is the case, but the point of this is, not always.

Remember, in the design considerations , you gear for maximizing HP over a rpm range. (not torque) . YOU can see from my engine plots, that if i designed gearing to maximize torque, average (or HP seconds ) would be extremely compromised. There are a lot of guys at the track that still think this way when they drive. they leave a lot of time on the table short shifting.

mark kibort

Ill use less than 40. And yes, mine was a joke too.

Credibility= saying something and being able to back it up with known, provable fact.

B.S. = Saying something is true without being able to prove it by fact, experience or accepted knowledge. Belief in this "truth", even though it has been disproved by someone creditable.

Bull

That is 47...

Veloce Raptor

That's great, Mark. Note the bolded word. My experience proves my point. Your experience, on the other hand, has you claiming that slicks are no quicker than Toyos.

Folks can make up their own minds about credibility...or "creditability"...or what has been "proved" or "disproved".







Professional Racing and Driving Coach

mark kibort

You are being plain silly now VR. You have no experience in all the possiblities of equal hp power plants with different torque values.

Tires?????? com'mon, Ive already said, slicks are the fastest, NO QUESTION there, it was Bryan that said that slicks would be slower than DOTs (hoosiers) on the first 2 laps. (On another thread)

Take a look at the Dez graph that i modeled after his own criteria. you would still pick the higher torque engine of the same HP??? If so, there goes your creditability! If not, why dont you finish this thread off by giving one logical reason why you would choose one of them over the other. So far you Creditability is nil, due to you just joking around being stubborn and arguing like a 7 year old. (and I mean that in the most constructive way possible )
Geez, where have I heard that before? All you do is tell us, from your HUGE experience data bank, that a high torque equal HP engines will out perform on a race track. You base this on what? the one time you drove a caddy and a M5 and saw 10mph down the straight difference and had NO idea what the hp and torque levels were of each. (not to mention the countless other factors)

mk

Veloce Raptor

..

ew928

I predict MK will get the last word in.

Don't think a 30 page corral will be big enough for this spill.