Well done you race cars. You are forgetting that on a race/rally engine they have been tuned to the maximum potential, most likely costing of high lift cams and the like, thus shifting the power and torque bands further up the rev range meaning high rpm gear changes are better suited in this situation.

We are talking about a run of the mill factory standard road car which has economy in mind when it was produced.

Sorry? Are we talking about the Fabia 1.4TDi or the vRS as the run of the mill standard road car that was produced with economy in mind?

I don't think Skoda's engineers gave a monkey's about economy when they shoehorned the biggest engine that would fit into the Furby's engine bay. I certainly don't recall any of the car reviews pointing out how it was a great Prius competitor?

And we are talking about the fastest way to accelerate a Fabia vRS. If you only rev to 3000rpm then you need 3 gear changes to hit 60mph. That's not the fastest acceleration. It's well slow. And please feel free to educate me as to why, on the Octavia CR170 vRS, a car which is sold with sporty credentials, the gearbox is programmed to change up at the red line in S mode, not to short shift even though the gear changes are so blisteringly fast it would make sense to?

Perhaps this wonderful CR170 diesel with dsg gearbox is still in the powerband at the redline, but I doubt it.

Your first arsey/know all comment was about the standard pd130 though, your just going on about different engines now cause you know your wrong.

The majority of turbo diesels are faster accelerating by staying in the high torque power band, try it.

If your ever lucky enough to drive a V8 M3 with circa 400bhp/400lb ft you will find that the power band on those is massive, and your never out of it.

The easy way to think of it is a car with higher torque figure than peak bhp accelerates faster in the high torque band,

A car with a higher bhp than torque accelarates faster keeping it as near to peak bhp point as possible.

Do people talk about power to weight ratio, or torque to weight ratio? :think:

 

Some good ideas about the physics here from 'Stingray' on page 1.

 

Edit:  my favourite bit of what he says,

 

" In a given gear, the instantaneous acceleration is highest at the torque peak. At a given speed, a vehicle allowed to select any gear ratio will have the highest instantaneous acceleration at the power peak. If that sounds contradictory, try reading it a couple of times. The first condition has you choose a gear and vary speed. In the second, you fix speed and vary the gear ratio"

 

[my emphasis].

 

That's an interesting quote from that thread, the whole post (that you pulled your quote from) also says;

 

Despite this, it is common practice for engines to be advertised only in terms of their peak torque and peak power. The engine speeds where those conditions may be found are also usually given. The peak power is very important for reasons I'll get to later, but the peak torque is essentially useless all by itself. The reason is that the gearbox can multiply the torque to (essentially) any amount whatsoever at an appropriate speed. But an ideal gearbox cannot change the power.

 

So, if you can change gears then peak torque is not that important.

 

 

Staying with the ideal case, the maximum forward force that a car can produce is entirely determined by the power its engine is producing and the car's overall speed. So fixing speed, maximum acceleration is always reached by maximizing the engine's power output. It is the job of the transmission (and driver) to use the gearbox to keep the revs as close to the engine's power peak as possible if full acceleration is desired.

 

So the driver has to keep the engine speed as close to peak power as possible, not peak torque.

 

Modern transmissions have many closely-spaced ratios, so except at very low speeds (at the bottom of 1st gear), an engine may be kept close to its power peak for as long as desired. That means that a well-designed car that is driven well may produce a force F∼P peak /v  . This depends only on the peak power (and velocity), and explains why the power-to-weight ratio is such a good predictor of acceleration performance.

 

Again, keep the engine as close to peak power as possible.

 

Having said that, the torque peak is not completely irrelevant. Its position relative to the power peak is usually a good indicator of the size of the car's "powerband." Essentially, how high do you have to rev it in a given gear before the engine really gets going? Having a wide powerband is extremely important in everyday (or moderately aggressive) driving where you're not going to redline in every gear. It makes the car feel much more powerful even if the maximum performance is the same. Of course, a wide powerband is also useful if your have a poor transmission or don't want to shift as much.

 

So the high torque low down makes the engine flexible and FEEL powerful. But note that the caveat is that you are not going to redline in every gear. To go fastest, you redline in every gear.

Perhaps this wonderful CR170 diesel with dsg gearbox is still in the powerband at the redline, but I doubt it.

Your first arsey/know all comment was about the standard pd130 though, your just going on about different engines now cause you know your wrong.

The majority of turbo diesels are faster accelerating by staying in the high torque power band, try it.

If your ever lucky enough to drive a V8 M3 with circa 400bhp/400lb ft you will find that the power band on those is massive, and your never out of it.

The easy way to think of it is a car with higher torque figure than peak bhp accelerates faster in the high torque band,

A car with a higher bhp than torque accelarates faster keeping it as near to peak bhp point as possible.

 

But it's not just the CR170. I just used that as an example because it's low-revving torquey engine where the speed of gear changing isn't a factor because the DSG gearbox takes care of that for you. Consistently. And the CR170 originally had a higher-revving, LOWER torque but higher power petrol equivalent that beat it in acceleration. And the newer petrols have the SAME torque as the CR170 (350Nm) but all these cars are still programmed by VAG to change up at the red line. Because that's fastest.

 

I've been VERY lucky in terms of my cars. I had a Lamborghini Gallardo LP570 Superleggera as my previous company car and I can assure you, you're always in what you call the powerband but it still accelerates fastest at the power peak and the recommended shift point in all gears for maximum performance is maximum revs.

 

The Fabia vRS is no different to any other car, petrol or diesel. It always accelerates fastest at peak power, not peak torque and you will always go faster by revving it harder. I know it doesn't feel like it, but it's true. 

 

Plus it's good for the engine to use the full rev range.

It's very simple wja, if you look at the dyno graph of a standard PD130 you will note that torque peaks at about 2000 rpm and power peaks at about 4000 rpm after which it tails off.

If you rev the engine past peak power before changing gear you will be going slower.

If you don't rev the engine enough and the revs drop below peak torque after the gear change then you will be going slower.

 

As long as you're using the gearbox to keep the engine accelerating between peak torque and peak power then that will give the best acceleration.

 

Why do you think weak clutches start slipping when you hit peak torque, it's because this is when the tractive force available is at its greatest and rather than accelerate the car the clutch slips.

 

As for remapping DSG gearboxes I can only imagine that this is only necessary if the engine has been modified to shift peak torque and peak power further up the rev range.

Power at the wheels is the pertinent figure. Produce a graph showing power vs speed for each of the gears and overlay them. Where they overlap, try to pick the biggest numbers.

It's very simple wja, if you look at the dyno graph of a standard PD130 you will note that torque peaks at about 2000 rpm and power peaks at about 4000 rpm after which it tails off.

If you rev the engine past peak power before changing gear you will be going slower.

If you don't rev the engine enough and the revs drop below peak torque after the gear change then you will be going slower.

As long as you're using the gearbox to keep the engine accelerating between peak torque and peak power then that will give the best acceleration.

Why do you think weak clutches start slipping when you hit peak torque, it's because this is when the tractive force available is at its greatest and rather than accelerate the car the clutch slips.

As for remapping DSG gearboxes I can only imagine that this is only necessary if the engine has been modified to shift peak torque and peak power further up the rev range.

Sorry, but you've veered away from what coskev said originally which was that there is no point revving the vRS beyond 3000 rpm because after that all the torque was gone. You are now saying that by accelerating beyond peak power to change up I will be going slower. Not so, I'm accelerating slower, but I'm still accelerating until I run out of revs. Maximum acceleration happens at peak power. If you change up before peak power you will never achieve maximum acceleration. By changing up at the maximum revs you put the engine speed AFTER the gear change where the manufacturer designed it to be for maximum acceleration. And that's near peak power, above peak torque.

That's why I'm a driver and I wouldn't employ you as any kind of engineer.

Power at the wheels is the pertinent figure. Produce a graph showing power vs speed for each of the gears and overlay them. Where they overlap, try to pick the biggest numbers.

I'm not sure I understand. Are you suggesting that somehow the power figure (measured at the wheels) moves up and down the rev range in the different gears?

I'm glad my reference to 'Stingray's' words was useful wja96, even if the quote I picked isn't the clearest! However many times I read it, it still seems contradictory.

 

The bits you quote make it much clearer that you're right on this issue. Why some people can change what they're saying in the direction of what you said from the start, whilst maintaining that they're right and you're wrong is a bit of a mystery to me... :think:

Sorry, but you can't be right. Maximum acceleration happens at peak power. If you change up before peak power you will never achieve maximum acceleration. By changing up at the maximum revs you put the engine speed after the gear change where the manufacturer designed it to be for maximum acceleration. And that's near peak power, above peak torque.

That's why I'm a driver and I don't employ you as an engineer.

 

Ok, suit yourself, I'm not going to bother arguing with you, you've had the information and if you were to choose to absorb it you will become a quicker driver.

I'm glad my reference to 'Stingray's' words was useful wja96, even if the quote I picked isn't the clearest! However many times I read it, it still seems contradictory.

 

The bits you quote make it much clearer that you're right on this issue. Why some people can change what they're saying in the direction of what you said from the start, whilst maintaining that they're right and you're wrong is a bit of a mystery to me... :think:

Thank you for posting the link. It was far more eloquent at describing what I wanted to say that I would have been.

Sadly, despite others trying to argue that every car manufacturer and racing driver in the world is wrong, I still feel that at least two people will still be encouraging Fabia vRS drivers to short-shift because it's somehow faster. Which it just can't be.

Ok, suit yourself, I'm not going to bother arguing with you, you've had the information and if you were to choose to absorb it you will become a quicker driver.

The problem with your 'information' is that it won't make me a quicker driver.

I would just like you (or anyone else) to explain WHY, if what coskev originally said was correct, and you asserted was correct too, do all car manufacturers that fit automatic gearboxes with performance or sports modes program those modes to Rev to the red line rather than peak torque, which you and coskev both assert is as much as you need for maximum acceleration?

The problem with your 'information' is that it won't make me a quicker driver.

 

That's nothing to do with science and everything to do with stubbornness, did you try plugging some figures into that equation I posted a link for?

 

 

I would just like you (or anyone else) to explain WHY, if what coskev originally said was correct, and you asserted was correct too, do all car manufacturers that fit automatic gearboxes with performance or sports modes program those modes to Rev to the red line rather than peak torque, which you and coskev both assert is as much as you need for maximum acceleration?

 

Look, it really depends on the spread of torque available, as long as the gearbox ratios suit that spread then all will be well, no amount of remapping will change the ratios or the final drive of a DSG gearbox, a DSG gearbox is simply an electronically actuated manual gearbox with the ability to pre select gears to enhance shift speeds, it doesn't have a fluid torque converter like true automatics do, a fluid torque converter is simply a slipping clutch that can't burn out (although the fluid does get hot as a result).

 

A CVT transmission which is often fitted to smaller cars is different again, it mechanically varies the gear ratio dynamically to allow the engine to operate at it's best efficiency, these transmissions often have electronic 'steps' programmed into the computer control system even though it doesn't need them because they reduce efficiency, they are put there because most drivers find it disconcerting to hear an engine maintaining constant revs as it accelerates.

 

Sports modes are part of this illusion, they allow the engine to rev on past it's peak efficiency because it is often more useful to hang onto a particular gear for longer when cornering enthusiastically because changing gear during hard cornering unbalances the car and can even cause an accident.

 

I would imagine that your Lambo had launch control, this system is designed to make it easier to launch the car without bogging the engine through too few revs or excessive wheelspin through too many. I also imagine that the actual gear changing part was down to you using the paddles to actuate the E-gear shift although there was probably a full auto mode where you could simply floor the pedal and the gearbox upshifted for you, I would also imagine that with the Lambo being German under the skin that the full auto mode would be optimised for best acceleration. Depending on which model you had, the V10 engine has quite a narrow powerband due to the high state of tune, nonetheless I would imagine that upshifts occurred at peak power, not after.

 

Turbodiesels also have quite a narrow powerband which is why they have close ratio six-speed gearboxes, I maintain that as long as you shift up at or before peak power and as long as the revs do not drop below peak torque then the car cannot accelerate any faster.

I'm not sure I understand. Are you suggesting that somehow the power figure (measured at the wheels) moves up and down the rev range in the different gears?

 

No, not that. The power curve is mapped onto speed using each gear ratio. You end up with a series of power curves with peaks. They overlap each other. Changing gear where they cross is supposed to be the ideal change point.

 

B*gger, I'm gonna have to do this now, aren't I? :(

No, not that. The power curve is mapped onto speed using each gear ratio. You end up with a series of power curves with peaks. They overlap each other. Changing gear where they cross is supposed to be the ideal change point.

 

B*gger, I'm gonna have to do this now, aren't I? :(

I'm 99.9% certain you don't have to because Skoda have already tuned the gearbox to the engine, so if you change up at the red line you should find the revs at the optimum place to keep the car accelerating as hard as possible. But please, don't let me stop you.

Tried and failed.... Actually, I feel it's a driving Excel failure than owt else.

Is it not straightforward to put an accelerometer app on a phone and directly measure what's happening as you experiment with different shift points? (Best if it's a passenger doing the phone thing, obviously. )

Is it not straightforward to put an accelerometer app on a phone and directly measure what's happening as you experiment with different shift points? (Best if it's a passenger doing the phone thing, obviously. )

I've got a RaceLogic vBox. I just need to get back to Norfolk and then find out when I can use the Old Buckenham runway for a couple of hours while I mess about getting the logs right.

But it's not just the CR170. I just used that as an example because it's low-revving torquey engine where the speed of gear changing isn't a factor because the DSG gearbox takes care of that for you. Consistently. And the CR170 originally had a higher-revving, LOWER torque but higher power petrol equivalent that beat it in acceleration. And the newer petrols have the SAME torque as the CR170 (350Nm) but all these cars are still programmed by VAG to change up at the red line. Because that's fastest.

 

I've been VERY lucky in terms of my cars. I had a Lamborghini Gallardo LP570 Superleggera as my previous company car and I can assure you, you're always in what you call the powerband but it still accelerates fastest at the power peak and the recommended shift point in all gears for maximum performance is maximum revs.

 

The Fabia vRS is no different to any other car, petrol or diesel. It always accelerates fastest at peak power, not peak torque and you will always go faster by revving it harder. I know it doesn't feel like it, but it's true. 

 

Plus it's good for the engine to use the full rev range.

fabia peak power at 3500rpm right? so past 4k its pretty useless

fabia peak power at 3500rpm right? so past 4k its pretty useless

Peak power (131PS) is at 4000rpm on both the ASZ and BLT engines.