Torque vs. HP

[Racebred]

Re: Torque vs. HP

i cant spot the pun...

 

[TripleM]

Re: Torque vs. HP

Yup... I enjoy this kinda thread. Especially when it enables me to (hopefully!) close the gap on track with the Spec C...

It should be the other way round....kekeke...

piggy
the 520d auto has 3.23 FD vs 530i 3.64

 

[goggomobil]

Re: Torque vs. HP

If you shift at peak torque or a little after peak torque to try and maximize area under the torque curve, then you end up with highest average crank torque, but when you factor in the gear ratios, your average wheel torque is lower (based on average petrol engine torque/power curves and average gearing gaps) so acceleration is not optimized.

If you shift beyond peak power or at redline in situations where peak power is close to redline, or where power does not fall sharply off beyond peak power, then you maximize area under the power curve and you have the highest average wheel torque. Acceleration is optimized.

You can work the shift points by power based or force based calculations and both in the end are the same, just mathematically different. You can also do it graphically by looking at power curves and knowing gearing gaps, maximize area under the power curve. The general rule though, and almost without exception with modern petrol otto cycle engines, is to shift at redline to maximize acceleration. This is just due to the shape of the curves and the gearing gaps.

CVT requires different strategy but we can leave that out since the system isn't perfected yet and not widely used, and also because the electronics do all the ratio changing automatically and the driver is no longer involved in shifting.



This is true, but often the ideal shift point is past redline. Often we run into redline before we would like to shift, and longevity taking precedence, we are forced to shift at redline.


It's not a myth, in fact it is almost a rule with modern petrol engines - especially so with sportier engines.

There are very few modern exceptions to this rule. For every 1 example to the contrary that is found, another 10 can be found in support of it. Pick any production car, with dyno chart, whose gear ratios are published, and it can be shown mathematically.




This has little to do with hp and torque and much more to do with mass, speed, frontal area, chassis strength.


Unless the torque fall off is very sharp, there is no reason to shift early. If it is unclear, it is easy enough to calculate the shift point.


What's important is the shape of the curves. It doesn't matter as much what the actual value is talking strictly in terms of determining shift points. As long as the curves are proportional and accurate, it doesn't matter if they are translated up or down along the Y axis.



Disagree. If you're doing force based calculation then you have to look not only at resulting crank torque after shift, but consider the new gear ratio you're now in as well to arrive at wheel torque.

It is very common not even to see peak torque RPM on an engine driven for performance - especially racing engines. And racing engines are engines that generally have torque peak closer to power peak, which underlines the point about how maximizing area under the power curve and shifting at redline is as close to a rule as you'll get to in shift point selection, and not shifting at peak torque, or shortly after peak torque.

========

I think it is easier to work a real example than to get lost in the fog. I'm sure you'll find most cars favour shifting at redline. Pick a production car that has lots of data published on it and crunch your numbers.... you'll see..

Right. For absolute optimum acceleration plot the torque at the driven wheels vs road speed for each gear ratio and use the curves to determine the best exact RPM to change gears.

For optimisation of acceleration in the real world, don't have to be so anal, depend on butt feel and experience with your vehicle to know when to shift.

Realistically, (leaving out the racing engines where power continues to rise well into the detonation zone), for a "sporty" normally aspirated engine (say M54) where torque curve is pretty flat and power doesn't drop off until close to or at the rev limiter, then change gear just before the limiter cuts in and you will find yourself in a fat part of the torque curve anyway (if the designer has done his job revs will not be too far off max torque).

 

[Shaun]

Re: Torque vs. HP

For optimisation of acceleration in the real world, don't have to be so anal, depend on butt feel and experience with your vehicle to know when to shift.

I don't think there's anything anal about spending 10 minutes to figure it out once and then sticking to it in in the future. Human feel is not sensitive enough, so the chances of repeatedly shifting wrong while thinking you're doing it right, are high. Quick quantification beats long and wrong intuition.

racing engines where power continues to rise well into the detonation zone

Detonation zones in race engines are in the bottom 50-60% of the engine speed range. High 5 digit engine speeds and higher RPM race engines, this percentage shrinks to the bottom 20-30%. All these ranges are below peak power, so the upper areas cannot be defined as a detonation zone.

The main requirement for detonation to occur is time. Time at required conditions - temperature, hence pressure indirectly. At higher engine speeds there is not enough time spent at those conditions and even if there is, the primary and intended flame front originating from the spark is right in the end gas zone and burning by the time In a race engines where engine speeds go into 5 digits, the det zone almost doesn't exist up high because cylnder is not getting charged very hard and because there is no time for detonation to occur. At 6000 RPM you have half the time at 3000 RPM, and at 9000 RPM, 1/3 the time. 12,000 RPM, 1/4 the time, and so on.

Modified street turbo engines are slightly different, but the general rule still applies, but with slightly higher engine speed percentages due to lack or charge at low engine speed and lower compression ratios, whilst the low-mid to mid range gets a real slug from decently sized turbos and sometimes too much ignition advance from overzealous tuners.

In all cases, detonation should be differentiated from pre-ignition which is not affected by the time factor, hence independent of engine speed.

for a "sporty" normally aspirated engine (say M54) where torque curve is pretty flat and power doesn't drop off until close to or at the rev limiter, then change gear just before the limiter cuts in and you will find yourself in a fat part of the torque curve anyway (if the designer has done his job revs will not be too far off max torque).

As you continue to shift at redline in the upper 2 or 3 gears, you will find that the operating range is moved away from peak torque because the gearing gaps get narrower (as they always do as gear number rises).

We must not confuse a desginer's desire for refined low and wide power with his targets for a shift strategy. It is easy to create low and wide power. The lower and wider your power spread is (table top torque curve), the higher your chances of ending up at peak torque or near peak torque right after a shift, even if you shift at random anywhere in the upper 40% of the engine speed range - a huge window.

Peak torque is never a reference point for selecting gears or shift points

 

[goggomobil]

Re: Torque vs. HP

The general rule though, and almost without exception with modern petrol otto cycle engines, is to shift at redline to maximize acceleration. This is just due to the shape of the curves and the gearing gaps.

An over generalisation, there are still many engines around that are have rather agricultural characteristics, but let's just assume that with the "sporty engines" that you mention this applies, so we should shift at redline in each gear. No disagreement here.

I don't think there's anything anal about spending 10 minutes to figure it out once and then sticking to it in in the future.

Now to truly optimise acceleration supose we spend the 10 minutes to work out the actual revs we should shift at in each gear (to the nearest rpm, since we are being rigorous) and we find that the best rpm to shift in each gear varies because torque curves are not absolutely flat and gear ratio spacing varies. Now what? We don't shift at redline any more but try to shift at the optimum revs for each gearchange (which will be close to the redline anyway by earlier arguments) let's say 6862rpm, 6927rpm etc etc. How close to these exact revs can we achieve, how accurately can we even read the tacho to do this? This is going beyond the point where it is practically useful, and therefore an_l.

Human feel is not sensitive enough, so the chances of repeatedly shifting wrong while thinking you're doing it right, are high. Quick quantification beats long and wrong intuition.

Don't underestimate human feel.

"the chances of repeatedly shifting wrong while thinking you're doing it right, are high". Hey!!!! don't underestimate us humans. Let's put Schummi in a car and don't tell him the optimum shift revs, let him drive around for a while, bet he works them out and gets real close pretty quick. Bet he even does it without a rev counter. OK extreme example but we all have the capability to learn (learning not the same as intuition), we are not Schummis but we will get pretty close to optimum for the vehicle we are familiar with, question is, will we (or can Schummi) do any better by tacho watching? I think not.



Ambiguous use of "detonation".

What I meant when I said "leaving out the racing engines where power continues to rise well into the detonation zone" was power being produced well into revs where the mechanical limits have been exceeded and the engine is in danger of going kaboom, and was clearly not a reference to detonation in the combustion chamber at lower revs. I should have said "self-destruction zone".


But never mind, we got an interesting and detailed explanation on the difference between detonation and pre-ignition.


cheers

goggo

 

[axl]

Re: Torque vs. HP

Keep it up guys... I'm sure the rest of the non-techies (like myself) appreciate this insightful discussion.

 

[ho2786]

Re: Torque vs. HP

Machine torque
Torque is part of the basic specification of an engine: the power output of an engine is expressed as its torque multiplied by its rotational speed. Internal-combustion engines produce useful torque only over a limited range of rotational speeds (typically from around 1,000–6,000 rpm for a small car). The varying torque output over that range can be measured with a dynamometer, and shown as a torque curve. The peak of that torque curve usually occurs somewhat below the overall power peak. The torque peak cannot, by definition, appear at higher rpm than the power peak.
Understanding the relationship between torque, power and engine speed is vital in automotive engineering, concerned as it is with transmitting power from the engine through the drive train to the wheels. Typically power is a function of torque and engine speed. The gearing of the drive train must be chosen appropriately to make the most of the motor's torque characteristics.
Steam engines and electric motors tend to produce maximum torque close to zero rpm, with the torque diminishing as rotational speed rises (due to increasing friction and other constraints). Therefore, these types of engines usually have quite different types of drivetrains from internal combustion engines.
Torque is also the easiest way to explain mechanical advantage in just about every simple machine.
http://www.bmw-sg.com/forums/
[edit] Relationship between torque, power and energy

If a force is allowed to act through a distance, it is doing mechanical work. Similarly, if torque is allowed to act through a rotational distance, it is doing work. Power is the work per unit time. However, time and rotational distance are related by the angular speed where each revolution results in the circumference of the circle being travelled by the force that is generating the torque. This means that torque that is causing the angular speed to increase is doing work and the generated power may be calculated as:

On the right hand side, this is a scalar product of two vectors, giving a scalar on the left hand side of the equation. Mathematically, the equation may be rearranged to compute torque for a given power output. However in practice there is no direct way to measure power whereas torque and angular speed can be measured directly.
In practice, this relationship can be observed in power stations which are connected to a large electrical power grid. In such an arrangement, the generator's angular speed is fixed by the grid's frequency, and the power output of the plant is determined by the torque applied to the generator's axis of rotation.
Consistent units must be used. For metric SI units power is watts, torque is newton-metres and angular speed is radians per second (not rpm and not revolutions per second).
Also, the unit newton-metre is dimensionally equivalent to the joule, which is the unit of energy. However, in the case of torque, the unit is assigned to a vector, whereas for energy, it is assigned to a scalar.

 

[titanic]

Re: Torque vs. HP

Am I correct to say that in order to get better 0-100km time, I should really be looking for higher torque over a high RPM range, rather than just higher peak torque? In addition 20" wheels should give me better 0-100km time than say 18" wheels (forget about weight first) because for the same RPM, I am covering more distance. Correct?

 

[Shaun]

Re: Torque vs. HP

An over generalisation, there are still many engines around that are have rather agricultural characteristics,

You have to get to very weirdly speced engines or low cost engines where the only reason the upper engine speed range exists is for some form of decent cruise speed. Like I said, there are almost no exceptions to the rule - especially in the context of the type of cars and drivers in this forum, or any other decently built marque.

Now to truly optimise acceleration supose we spend the 10 minutes to work out the actual revs we should shift at in each gear (to the nearest rpm, since we are being rigorous) and we find that the best rpm to shift in each gear varies because torque curves are not absolutely flat and gear ratio spacing varies. Now what? We don't shift at redline any more but try to shift at the optimum revs for each gearchange (which will be close to the redline anyway by earlier arguments) let's say 6862rpm, 6927rpm etc etc. How close to these exact revs can we achieve, how accurately can we even read the tacho to do this? This is going beyond the point where it is practically useful, and therefore an_l.

No driver-controlled shifting (street or race) in thie world is to the nearest RPM. The human and the tach don't work to the last RPM. You are setting your own unreasonable definition of data application and then calling it anal. Using human feel you miss by far more than single digits, more like triple digit engine speeds at least. Your references to peak torque and fat torque, etc. .....these points relative to peak power, redline are 4 digit engine speeds apart. So when I suggest you do the math and find out, I mean more precision than you inaccurate feel, and your inaccurate theory about shifting to land at peak torque or near it. All this is missing by hundreds and thousands of RPM, which can be easily cut down.

Don't underestimate human feel.

"the chances of repeatedly shifting wrong while thinking you're doing it right, are high". Hey!!!! don't underestimate us humans. Let's put Schummi in a car and don't tell him the optimum shift revs, let him drive around for a while, bet he works them out and gets real close pretty quick. Bet he even does it without a rev counter.

You are making assumptions again. It has been found that the human body is poor at sensing speed and acceleration (second derivative). It is really only is sensitive to jerk (3rd derivative) . People involved in production car ride and handling, or race driver development know this.

OK extreme example but we all have the capability to learn (learning not the same as intuition), we are not Schummis but we will get pretty close to optimum for the vehicle we are familiar with, question is, will we (or can Schummi) do any better by tacho watching? I think not.

See para 1

What I meant when I said "leaving out the racing engines where power continues to rise well into the detonation zone" was power being produced well into revs where the mechanical limits have been exceeded and the engine is in danger of going kaboom, and was clearly not a reference to detonation in the combustion chamber at lower revs. I should have said "self-destruction zone".

Within design limits and street level margin of safety, the engine is in no greater danger of destroying itself at upper engine speeds. Surely you aren't going to label your mid range engine speed a self-destruction zone, referencing it to low engine speeds just a little over idling?

But never mind, we got an interesting and detailed explanation on the difference between detonation and pre-ignition.

I didn't say anything about pre-ignition except that it is not time dependent. I didn't even characterize detonation except explain one of its largest factors - time.

====

Titanic, larger rolling circumference almost always slow you down acceleration wise. You're effectively gearing up your car.

I should really be looking for higher torque over a high RPM range, rather than just higher peak torque?

Yes! Note also that high torque at high RPM, equals high power. They are mathematically inseparable.

 

[TripleM]

Re: Torque vs. HP

Am I correct to say that in order to get better 0-100km time, I should really be looking for higher torque over a high RPM range, rather than just higher peak torque? In addition 20" wheels should give me better 0-100km time than say 18" wheels (forget about weight first) because for the same RPM, I am covering more distance. Correct?

I think u r correct on the first one..
U can also play with FD ratio for quicker acceleration but there are "side effects" to comprehend. For eg, u will lose your top end speed, you will have louder engine noise, your fuel consumption may go up, you will have to shift more....

now regarding the 20in vs 18in argument..
Basic physics apply here

Conventionally speaking, larger wheel is faster but the smaller wheel allows quicker acceleration. This is because the smaller wheels hv less inertia to overcome and larger wheels have a higher road speed for the same rotational speed.

Several factors that contribute to larger wheels being less rolling resistant:
1. They won't drop as much into a smaller hole vs a smaller wheel
2. They hv higher leverage for lifting teh wheels over bumps
3. They have less deformation of the tires at the contact patch on the ground
4. Smaller wheels typically require faster chain speeds which mean they will induce higher frictional losses

Now, having said all those....differences that can be experienced may not be like heaven and earth. Generally speaking, smaller wheels should make sense for short standing sprints on tracks or autocross but in most applications, the rolling resistance of larger wheels should win.

Hope I made some sense here

 

[SubZero]

Re: Torque vs. HP

Conventionally speaking, larger wheel is faster but the smaller wheel allows quicker acceleration. This is because the smaller wheels hv less inertia to overcome and larger wheels have a higher road speed for the same rotational speed.

Generally, a wheel with a 20" rim and one with a 18" rim should have the same rolling diameter if the proper inch up practice is followed. Therefore, both wheels would have the same road speed for the same rotational speed.

Here's a different reasoning to larger wheel diameters:

If one is to assume that the 20" rim wheel is bigger, the force transmitted to the ground will be lower than a smaller wheel for the same torque at the wheel by a percentage proportional to the difference in diameters. Torque = Force x Distance, distance here being the radius of the wheel. Lower force will mean lower acceleration by this percentage. But this wheel will indeed have a higher road speed for the same rotational speed by the same percentage. So, in the end it is a zero-sum game.

Is this reasoning correct? or something is amiss?

But what you said about the smaller wheel having a lower inertia would eventually be a criteria in differentiating acceleration, and of course wheel weight between the 2 different wheel types.

 

[goggomobil]

Re: Torque vs. HP

Like I said, there are almost no exceptions to the rule - especially in the context of the type of cars

and drivers in this forum, or any other decently built marque.

I think you have just told us that there are exceptions and and have even tried to define them.

No driver-controlled shifting (street or race) in the world is to the nearest RPM. The human and the tach don't

work to the last RPM.

Exactly. It was the point I was trying to make. So when does Schummi decide when to shift? At the redline? or exactly at

the calculated optimum shift revs? or when he decides to based on his real world driving inputs?

You are setting your own unreasonable definition of data application and then calling it anal.

No. It is application of data beyond what can be applied practically.

You have missed the point. I was generally agreeing with your earlier statement; "The general rule though, and almost

without exception with modern petrol otto cycle engines, is to shift at redline to maximize acceleration" (except that I

thought it was over generalising - see first point above).

so to simplify;

1. Shift at redline (agreed)

2. To optimise acceleration work out the best RPM shift points with the curves. (also agreed, read earlier post).

3. (2) is not going to be exactly at (1) but will be a little way above or below. Won't be too far off assuming what you

have been saying about these engines is true.

4. It is not practical for me to shift at exactly the calculated rpm, because I don't have time to watch the tacho, I can't

read it to that resolution anyway, and there are other factors in real world driving.

5. so do I try to shift at redline? or calculated optimum rpm?

6. Working out that optimum shift was just some tens of rpm off redline (for example only) was a good exercise but I can't

apply it.

7. anal

Using human feel you miss by far more than single digits, more like triple digit engine speeds at least.

Sounds like about as close as we can get by reading the tacho (bear in mind I have to do many other things while driving like

keeping my eyes on the road), and we won't even get into the subject of tachometer accuracy under dynamic conditions let

alone reading accuracy here.

You are making assumptions again.

What assumptions are you referring to, that humans should not be underestimated or that Schummi will find the best shift

points (or close) without having to calculate it no problem?

It has been found that the human body is poor at sensing speed and acceleration (second derivative). It is

really only is sensitive to jerk (3rd derivative) . People involved in production car ride and handling, or race driver

development know this.

Wait a minute. How is "poor" defined, under what test conditions, and in which study has this been found? Just saying

"People involved in production car ride and handling, or race driver development know this", is not sufficient to

substantiate your sweeping statement.

Close your eyes you may not know your speed but acceleration and rate of change of acceleration the human body can certainly

sense (and although the derivative of acceleration is called "jerk" this is misleading to the layperson as it implies a sharp

or step change, prefer to use rate of change of acceleration in this context). This ability to sense acceleration and its

rate of change is exactly why we can feel of how our vehicle acceleration changes, and with experience is an important input

into deciding when to shift.

By the same argument, when we go around corners, do we sense lateral accelerations, listen to the sound of the tyres etc. (so

we judge when we are losing grip) and drive accordingly or do we calculate it from the radius of the curve and coefficient of

friction between tyre and road etc. and drive to that? Sure we can work out the theoretical ultimate cornering speed under

ideal conditions but do we then corner by watching the speedometer (since by your definition our butts are so poor at sensing

speed and acceleration)? Surely not.

Within design limits and street level margin of safety, the engine is in no greater danger of destroying itself

at upper engine speeds. Surely you aren't going to label your mid range engine speed a self-destruction zone, referencing it

to low engine speeds just a little over idling?

Certainly not. Please read again, I was talking about race engines being capable of revving themselves to destruction

(meaning excessively high revs beyond design limits, ok no rev limiter etc.). You are choosing to dwell on "detonation" in

the combustion chamber.

 

[Shaun]

Re: Torque vs. HP

Exactly. It was the point I was trying to make. So when does Schummi decide when to shift? At the redline? or exactly at
the calculated optimum shift revs? or when he decides to based on his real world driving inputs?

Race drivers, F1, sub F1, and above low level formulae, have progressive shift lights come on at different rates depending on gear, which max out at the calculated optimum shift point (dependent on gear ratio), though this is always redline talking strictly in terms of acceleration.

So actual shift points are very close to optimum, not many hundreds or thousands of RPM away from optimum.

No. It is application of data beyond what can be applied practically.

I have described practical application. Many others apply it practically, using both visual and aural cues. In taller geared, large speed range cars, no aids are necessary because engine speed is rising slow enough to watch.

Just because you consider it impractical, doesn't mean it is so.

4. It is not practical for me to shift at exactly the calculated rpm, because I don't have time to watch the tacho, I can't read it to that resolution anyway, and there are other factors in real world driving.

5. so do I try to shift at redline? or calculated optimum rpm?

4. You can read and react to your tacho in your street car better than a resolution of 250 RPM. You can miss a shift point by 2000 RPM (factor of 8) if you go by intuition and feel (which is not accurate)

5. Common sense dictates that it depends on he difference between optimum and redline (IF it isn't redline or past redline). If optimum is 6489 and redline is 6500, then you can't make out that difference and it's up to you to try, but even if you shift at redline you're off by 11 RPM, not much at all. If optimum is 6000 and redline is 6500, then obviously you aim for optimum. If optimum is anything beyond redline, then you still shift at redline for longevity concerns.

6. Working out that optimum shift was just some tens of rpm off redline (for example only) was a good exercise but I can't

apply it.

7. anal

You are the only one who has suggested mandatory shifting within tens of RPM of optimal, and then you have gone ahead and labelled it anal. So this anal creation is all yours.

Sounds like about as close as we can get by reading the tacho (bear in mind I have to do many other things while driving like keeping my eyes on the road), and we won't even get into the subject of tachometer accuracy under dynamic conditions let alone reading accuracy here.

If you have no time to glance at the tacho when conditions for performance driving exist, then I'm not sure you're much of a driver. Street car engine speed changes are not too quick and in general, as they get quicker, so does the quality of the tach (less damping, quicker response), so either way it is going to be close under dynamic conditions.

What assumptions are you referring to, that humans should not be underestimated or that Schummi will find the best shift points (or close) without having to calculate it no problem?

You assume it will be simpler to feel your way to it, but it won't be.

How is "poor" defined, under what test conditions, and in which study has this been found? Just saying "People involved in production car ride and handling, or race driver development know this", is not sufficient to substantiate your sweeping statement.

Poor defined as bad, as inaccurate under common accelerations. I don't know the study. I know the concept has been confirmed by a range of sources, including a senior RH and NVH engineer for Ford who has worked for Lotus and Jaguar as well, a combat pilot and combat pilot trainer, the inventor and designer of a head restraint system set to rival HANS, my own race team's race engineer, driver development coach and race driver, and an R&D and technical director for F1 with over 20 years experience.

Never once have I heard that a race driver or other human can accurately determine acceleration, or best shift points by feel.

Close your eyes you may not know your speed but acceleration...the human body can certainly sense... This ability to sense acceleration and its rate of change is exactly why we can feel of how our vehicle acceleration changes, and with experience is an important input
into deciding when to shift.

No, when you drive you have visual input like scroll speed. There are also aural inputs but you are not actually sensing acceleration though feel. In the higher speed ranges and with a lack of markers or nearby objects for scroll, you rapidly lose all ability to sense speed and acceleration. Even at low speeds, the visual input is very poor resolution and does not correlate well to acceleration.

You are really only sensitive to change in tension in your neck muscles which is directly related to change in accel. - jerk. Pressure sensing via the back and back of your head is present, but poor, not enough "resolution" to determine best accel.

By the same argument, when we go around corners, do we sense lateral accelerations, listen to the sound of the tyres etc. (so we judge when we are losing grip) and drive accordingly or do we calculate it from the radius of the curve and coefficient of
friction between tyre and road etc. and drive to that? Sure we can work out the theoretical ultimate cornering speed under ideal conditions but do we then corner by watching the speedometer (since by your definition our butts are so poor at sensing speed and acceleration)? Surely not.

Cornering is not the same as picking shift points because when you are cornering as quick as you can and reach the limit, the vehicle will let the driver know by yaw acceleration changing quickly and obviously (again, this is jerk). Longitudinal acceleration has no obvious signs indicating poor acceleration, or best acceleration.. there is no stepping over the limit in most street car long. accel. , but there is with lat. accel, even with the cheapest, slowest cars you can buy.

Also, the calculation for optimal corner speeds involves dynamics and calculation at the masters and doctorate levels, since tire dynamics that are still not completely understood are involved, so the models are still somewhat inaccurate. On the other hand, picking best shift points for best accel. involves only primary school math.

Certainly not. Please read again, I was talking about race engines being capable of revving themselves to destruction (meaning excessively high revs beyond design limits, ok no rev limiter etc.). You are choosing to dwell on "detonation" in the combustion chamber.

In my last post to you I did not refer to CC detonation in any way.

Any engine is capable of revving itself to destruction without a rev limiter and beyond design limits. I dare say all modern production EFI engines have a rev limiter. I don't see the point in drawing up unreasonable situations that do not exist.

In any case, remember that your original statement was "leaving out the racing engines where power continues to rise well into the detonation zone". Now in your latest statements you are defining your wrongly terms "detonation zone" as "meaning excessively high revs beyond design limits". You are confusing yourself because nearly all engines have power falling before redline, and it only continues to fall past redline. If an engine has peak power at redline, then it has not been designed right. This applies to both street and race engines. Power does not continue to rise well into the revs that are beyond design limit. In fact, if the area beyond the design limit is not mapped properly or at all, and assuming there is no rev limit like you have suggested, then power will not only be dropping off, but plain fall flat on its face to negative power at the crank because all that's left is friction - and that those engine speeds, friction is huge, so expect a large negative power number because engine speed falls back into mapped range. This is assuming the engine has even survived mechanically..

 

[titanic]

Re: Torque vs. HP

Generally, a wheel with a 20" rim and one with a 18" rim should have the same rolling diameter if the proper inch up practice is followed. Therefore, both wheels would have the same road speed for the same rotational speed.

Good point, the rolling diameter would be the same with proper inching up. But if the 20" wheel also have wider track width, would that give me better acceleration?

 

[Shaun]

Re: Torque vs. HP

Good point, the rolling diameter would be the same with proper inching up. But if the 20" wheel also have wider track width, would that give me better acceleration?

Wider track helps longitudinal accel. under lateral accel. (mixed accel). by reducing lateral weight transfer.

If you are referring to wider tires themselves helping acceleration, it depends heavily on tire construction. Unlike say a solid steamroller wheel where doubling width at similar diameter, doubles contact patch, tires are elastic and assuming inflation pressures stay the same, as width increases (area increase), deformation at ground-tire interface decreases because there is less unit load per area. What you end up with is a contact patch that is wider, but shorter longitudinally. This reduces slip angle required to reach peak lateral force in the tire, making for more direct steering response. What low profile tires allow you to do is run lower pressures to increase contact patch area yet not have the tire squirm around on its sidewalls under lateral loads, since the sidewalls are inherently shorter and stiffer.

So it is all positive as long as the tire is contructed to allow reduction in inflation pressure and still end up with sufficiently stiff sidewalls, or as long as at a similar pressure, the tire is constructed less stiff radially to allow it to deform more and yield larger contact patch, and yet at that reduced radial stiffness, maintain or raise its lateral stiffness. Performance tire manufacturers often achieve these goals and together with superior compounds, is how wide performance tires allow better acceleration in all directions at higher responsiveness.

 

[goggomobil]

Re: Torque vs. HP

Race drivers, F1, sub F1, and above low level formulae, have progressive shift lights come on at

different rates depending on gear, which max out at the calculated optimum shift point (dependent on gear ratio), though this
is always redline talking strictly in terms of acceleration.
So actual shift points are very close to optimum, not many hundreds or thousands of RPM away from optimum.

OK agree redline and optimum very close perhaps few hundred or even tens of rpm from redline, so shift at redline

I have described practical application. Many others apply it practically, using both visual and aural cues.

Glad you brought up Visual and aural cues - both human senses, contribute towards "feel". Are you recognising the importance

of sensory input now?

4. You can read and react to your tacho in your street car better than a resolution of 250 RPM. You can miss a
shift point by 2000 RPM (factor of if you go by intuition and feel (which is not accurate)

Did I say take the tacho out of the car or avoid looking at it? Point (1) in my previous post; agree - shift at redline (use

tacho).

5. Common sense dictates that it depends on he difference between optimum and redline (IF it isn't redline or
past redline). If optimum is 6489 and redline is 6500, then you can't make out that difference and it's up to you to try, but
even if you shift at redline you're off by 11 RPM, not much at all. If optimum is 6000 and redline is 6500, then obviously
you aim for optimum. If optimum is anything beyond redline, then you still shift at redline for longevity concerns.

Difference between optimum and redline small by your arguments, so shift at redline, especially on sporty or racing engine.

I guess there's a myth out there that changing gears at redline get the best acceleration of the car.

It's not a myth, in fact it is almost a rule with modern petrol engines - especially so with sportier

engines.

agree again shift at redline

You are the only one who has suggested mandatory shifting within tens of RPM of optimal, and then you have gone
ahead and labelled it anal. So this anal creation is all yours.

No I did not, I have agreed with all your statements above - which is to shift at redline. I suggested that trying to shift

at the optimum which is close to but not actually at the redline and which is at different rpm for each gear ratio is anal.

If you have no time to glance at the tacho when conditions for performance driving exist, then I'm not sure
you're much of a driver.

Did I say no time to glance at the tacho? I meant to sufficiently accurately read the tacho to get close to the optimum

points you will need to more than just glance at your perfectly accurate tacho.
Ouch!! I'm sure you are a fantastic driver.

Poor defined as bad, as inaccurate under common accelerations. I don't know the study. I know the concept has

been confirmed
by a range of sources, including a senior RH and NVH engineer for Ford who has worked for Lotus and Jaguar as well, a combat
pilot and combat pilot trainer, the inventor and designer of a head restraint system set to rival HANS, my own race team's
race engineer, driver development coach and race driver, and an R&D and technical director for F1 with over 20 years
experience. Never once have I heard that a race driver or other human can accurately determine acceleration, or best shift
points by feel.

2 separate points,
1. I'm convinced, shift at redline so not much point in using optimum shift points (see above)
2. Your sweeping statement about human feel. Don't underestimate humans. If Schummi (sorry got to use him again) loses

his rev counter in the middle of a race, is he still going to be quick or is he going to slow down drastically (which he

should be if going by your arguments he may shift thousands of revs off optimum). Of course his visual, aural and sensing of

vibration levels, experience of the car and circuit etc also comes in, no one has restricted the definition of human feel to

sensing acceleration only.
You say poor, bad inaccurate, how much accuracy is actually required?? Any names or numbers from the study, or a reference?

Should be an interesting read.

Cornering is not the same as picking shift points because when you are cornering as quick as you can and reach

the limit, the
vehicle will let the driver know by yaw acceleration changing quickly and obviously (again, this is jerk).

Disagree, yaw acceleration at the limit can change quickly or not so quickly depending on the vehicle, tyres suspension
design, conditions etc. By the same token, if longitudinal acceleration changes this is also jerk. If you insist that

humans can only sense
quick and obvious changes in acceleration, you will have to quantify quick and obvious, and define poor, bad, inaccurate. If

a proper study has been done, then there will be some quantifiable conclusions eg. the average human can sense jerk of x

magnitude. You cannot just say it is known to be poor, and apply it to your specific situation, just because these engineers

and pilots and whoever said it. This is not doing justice to the people who actually did the study and who no doubt put

numbers to their findings.

Also, the calculation for optimal corner speeds involves dynamics and calculation at the masters and doctorate
levels, since tire dynamics that are still not completely understood are involved, so the models are still somewhat
inaccurate. On the other hand, picking best shift points for best accel. involves only primary school math.

Your primary school math syllabus is way ahead of mine.

OK now quoting what you said earlier

It is very common not even to see peak torque RPM on an engine driven for performance - especially racing

engines.

Now if we don't see peak torque RPM peak torque must occur above
redline revs.

You are confusing yourself because nearly all engines have power falling before redline, and it only continues

to fall past redline. If an engine has peak power at redline, then it has not been designed right. This applies to both

street and race engines. Power does not continue to rise well into the revs that are beyond design limit.

Contradiction?

 

[louis]

Re: Torque vs. HP

hmm, ok, may i ask, if torque is mathematically linked to HP, why do some engines have high peak torque and lower peak HP whereas others have high HP but low torque?

 

[gasterus]

Re: Torque vs. HP

HP: how fast your engine can run
TQ: how strong your engine can run

 

[Crufty Dusty]

Re: Torque vs. HP

hmm, ok, may i ask, if torque is mathematically linked to HP, why do some engines have high peak torque and lower peak HP whereas others have high HP but low torque?

It's very simple. Refer to the equation, and Shaun's earlier posting. High torque at high RPM = high HP. This is what is ideal for a performance engine, because you can make use of gearing.

For a street car, people prefer higher torque at lower RPM so you don't have to rev the nuts off the engine just to overtake. Meaning longer engine life and "quicker" perceived response, ceteris paribus.

 

[Crufty Dusty]

Re: Torque vs. HP

HP: how fast your engine can run
TQ: how strong your engine can run

You didn't read the earlier posting. :yikess: