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Author Topic: What does "more torque" do to a car's performance?  (Read 44953 times)

Nizzle

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Hi,

Next week, i'll be "eco-chipping" my car. I'll have experts rewrite my motor management software to make it more fuel efficient, with a 5-10% increase in range with a full gastank by optimizing valve timings in the 1500 - 2500 rpm range. They will also make my acceleration pedal feel more like the "old mechanical systems" instead of the current "drive by wire", and they will also increase my torque from 350 to 400 Nm, but my BHP/kW will remain the same (since increasing BHP without informing the taxation authorities is illegal here).

So my question is: "What performance differences can I expect with this Torque increase while my maximum Power stays the same?"

peppercorn

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Re: What does "more torque" do to a car's performance?
« Reply #1 on: 23/03/2012 15:45:31 »
An increase in torque, or turning force, ought to translate (w.r.t a vehicle) to an increase in acceleration. When a figure for torque is listed by a manufacturer it is actually the engine's peak torque they are quoting and it normally is stated for particular engine revs.

I'm interested to hear the explanation of how increasing torque is going to make for a more economical vehicle.  It may be that, by remapping, the tuners are actually changing where the torque curve reaches it's peak, so that it has a more suitable range for non-performance driving.
Remember car companies want to make sure the motoring journalists will describe their latest model as 'exciting' or 'responsive'. They are selling an image not an everyday tool for going from A to B.  Some mod'ers install taller gear ratios (especially for 'Top') to allow the engine to operate at lower revs for an ideal cruise speed, but this usually lowers acceleration as well.

Geezer

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Re: What does "more torque" do to a car's performance?
« Reply #2 on: 24/03/2012 08:08:35 »
It could be better, it could be worse, or it might not make any difference. It's not really meaningful to talk about "more torque" without specifying the relationship between speed and torque in the form of a graph.
 
To illustrate the point, I might produce an engine that can produce a lot of torque between 3000 and 3050 rpm, but outside of that speed range it hardly produces any torque at all. If I had a transmission with a lot of gear ratios, or an infinite number of ratios, I could probably still use that engine as long as the engine speed was kept in that tight band when I wanted to accelerate.
 
The engine's torque characteristic has to be carefully matched to the transmission's capabilities.
 
 
 

Lmnre

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Re: What does "more torque" do to a car's performance?
« Reply #3 on: 25/03/2012 13:30:55 »



Here's a very nice representation of power, torque and fuel consumption. The torque curve is generally flat over the useful rpm range (shown above by the line of short dashes, which is somewhat "humped"). The power curve is generally ramping over the useful rpm range (shown above by the line of long and short dashes). The fuel consumption curve is generally bathtub-shaped over the useful rpm range (shown above by the solid line).

Power is torque times rpm (along with a conversion factor), so you see now that a flat torque curve (ie, torque = constant) produces a ramping power curve. Only when the engine dramatically loses torque in the high end (high rpm), does the peak/flatten and drop off.

Torque is force acting on a lever arm, and just as your leg pushes on a bike's pedal, the engine's pistons push on their cranks, producing torque. If you weigh 150 lbs and stand with one foot on a pedal on a ˝-foot crank that's parallel with the ground (and thus, perpendicular to your weight vector), you are producing 75 ft-lbs of torque (150 lbs × ˝ ft = 75 ft-lbs). At the wheel, the torque acting through the tire's radius (from center to tread) produces a corresponding push (thrust). So, torque translates into thrust. A moving car produces "drag" (aerodynamic and rolling friction), which counters the thrust. Any thrust not opposed by drag will accelerate the car. The car will accelerate until the drag equals the thrust.

Power is torque times rpm, which translates into force times speed. One power measurement is ft-lb/sec, or in terms of force times speed, lb × ft/sec (same thing). The power peak in the diagram above occurs at about 6,000 rpm at WOT ("wide open throttle", aka pedal to the floor).

The fuel consumption graph shows the low/economical consumption in about the 2,500 to 4,500 rpm range. Below and above this range, the engine is less efficient for a variety of reasons. For these and other reasons, most driving occurs in this range.

Your eco-chipping will increase the torque throughout your useful rpm range (you essentially said your peak torque would increase from 350 to 400 Nm), which will also increase your power in that range (because power equals torque times rpm). However, bumping up the power in that range (only) won't affect your maximum power, which is in the high end. Probably the real reason why your maximum power doesn't change is because the top end (high rpm) performance of your engine has nothing to do with economy. The convenience of not having to inform your taxation authorities is just a benefit or assurance for you that they haven't made your car "illegal" and forced you to pay higher taxes. However, to be sure, the experts probably ensured that their tweaking did not affect your high rpms. If these experts were "hotrodding" your car, they would probably be increasing your maximum power.

So, the performance difference that you ask about is that your car will have a little more "spunk" in the low rpm range (more thrust), which is where you do some/most of your driving. And as you said about economical performance, it will increase by 5 to 10%. This means that your fuel consumption curve will drop by a similar amount in your usual rpm range.

Nizzle

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Re: What does "more torque" do to a car's performance?
« Reply #4 on: 26/03/2012 05:00:14 »
I'm interested to hear the explanation of how increasing torque is going to make for a more economical vehicle.

Me too :)
I'm not sure if this is a consequence of their fuel efficiency procedure or something "extra" that they do...
I know the main procedure will be valve timing adjustments. Maybe optimizing them creates extra torque? I will ask them as many questions as possible. Apparently these guys love to explain stuff to their customers according to the reviews of previous customers.
I like this graph Lmnre, and I'm hoping to get one with my test results before and after, and if I do, I'll make sure to scan it and post it here :)

Lmnre

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Re: What does "more torque" do to a car's performance?
« Reply #5 on: 31/03/2012 00:33:56 »
I'm interested to hear the explanation of how increasing torque is going to make for a more economical vehicle.
What happens is this. They say it'll increase torque from 350 to 400 Nm. A generic claim (ie, no rpm mentioned) means that they're probably talking about increasing the maximum torque (for example, in my diagram, torque peaks at about 4500 rpm). That torque curve is at the optimum throttle position (for maximum torque), and for the sake of simplicity, let's say that the optimum throttle position throughout all rpm is WOT (wide open throttle). Also for simplicity sake, let's say the eco-chipping elevates the whole torque curve by 14% (the increase from 350 to 400 Nm), except that eco-chipping effect tapers off toward the high end so it doesn't effect maximum power.

Let's talk about driving a steady 60 mph on the highway. You'll still drive 60 mph in high gear, and so, the engine rpm will be the same. Before the eco-chipping, you were driving a steady 60 mph at POT (partial open throttle). And after the eco-chipping, you will drive a steady 60 mph at a POT that's less than before. This means burning less gasoline.

I wonder why the car maker didn't do this originally from the factory, and boast a higher mpg. Maybe it causes the engine to run hotter, or have higher chamber pressures, causes the spark plugs to foul, increases pollution emissions, etc. I'm guessing there's some adverse side-effect that these eco-chippers aren't telling you.

Geezer

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Re: What does "more torque" do to a car's performance?
« Reply #6 on: 31/03/2012 01:29:27 »

You'll still drive 60 mph in high gear, and so, the engine rpm will be the same. Before the eco-chipping, you were driving a steady 60 mph at POT (partial open throttle). And after the eco-chipping, you will drive a steady 60 mph at a POT that's less than before. This means burning less gasoline.
 

I'm afraid it does not. If the throttle is "less open" the pumping losses will be greater which means the engine could be less efficient.
 
One of the reasons that diesel engines have a higher thermal efficiency than petrol engines is because they don't have a throttle.

syhprum

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Re: What does "more torque" do to a car's performance?
« Reply #7 on: 31/03/2012 07:14:38 »
To quote Nizzle
"I know the main procedure will be valve timing adjustments"
Are there any engines where valve timing is under electronic control ?, my BMW has variable valve timing but I understood it was a purely mechanial arrangement.

Geezer

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Re: What does "more torque" do to a car's performance?
« Reply #8 on: 31/03/2012 07:45:03 »
To quote Nizzle
"I know the main procedure will be valve timing adjustments"
Are there any engines where valve timing is under electronic control ?, my BMW has variable valve timing but I understood it was a purely mechanial arrangement.

I think there are some fancy arrangements to control the timing electro-mechanically, but AFAIK the actuation is ultimately mechanical-hydraulic. It takes a wicked amount of force to compress those springs!
 
It might be possible to eliminate camshafts entirely and use purely hydraulic actuators, but I suspect that would end up consuming more energy than it saved. The other problem is that a minor problem could easily result in the ever popular "valve goes through piston and wrecks entire engine" problem.
 
My hemi uses a simpler solution. It turns off four of the cylinders when it doesn't need them! It actually prevents the valves from opening at all, but I'm really not sure how it does it (and I'm not about to rip it apart to find out.)
« Last Edit: 31/03/2012 07:47:30 by Geezer »

Lmnre

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Re: What does "more torque" do to a car's performance?
« Reply #9 on: 31/03/2012 13:18:37 »
With 14% more torque all throttle positions, less air flowing into the cylinders at the same fuel-air mixture would result in less fuel burned for the same torque. No?

SeanB

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Re: What does "more torque" do to a car's performance?
« Reply #10 on: 31/03/2012 17:51:18 »
Most of the fuel economy comes from the new map being more concerned with the low end of the rev range. If you can get higher torque at lower revs, where the motor will be running most of the time, or can get higher power at a speed consistent for motorway use, then you use less fuel to drive at that speed.

Of course the biggest economy gain comes from the driver, years ago my father had an experienced German driver out from MB to do driver training for new trucks, and a few of his drivers could turn in similar fuel consumption figures in city and long distance driving, much to the MB trainer's surprise. One, a long time driver, could consistently better him, from long experience of local conditions and changing traffic patterns. Not bad for a driver who only had an education up to 16 before starting to work.

Geezer

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Re: What does "more torque" do to a car's performance?
« Reply #11 on: 31/03/2012 18:18:03 »
With 14% more torque all throttle positions, less air flowing into the cylinders at the same fuel-air mixture would result in less fuel burned for the same torque. No?

It would if that were to actually happen, but it can't happen.
 
The power output of the engine has to remain the same to move the vehicle at a certain speed against wind resistance on a level surface and, unless something amazing happens to dramatically improve the efficiency of the engine, it still has to burn fuel at the same rate to produce the same amount of power, and that means it needs the same mass flow of air to burn the fuel.
 
If the mass flow of the air is the same, but the throttle opening is reduced, the air velocity through the throttle has to increase, and that increases the pumping loss.
 
Torque is interesting, but it doesn't tell you anything about energy conversion unless you multiply it by speed, which makes it a measure of power. The only reason a change in the torque curve of an engine might improve fuel economy is if it allows the engine to operate for longer periods at its most efficient speed, but if that's the case it suggests the vehicle's gearing could be more apppropriate. It also explains why the automobile industry keeps increasing the number of gear ratios in transmissions.
 
 

Nizzle

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Re: What does "more torque" do to a car's performance?
« Reply #12 on: 02/04/2012 05:53:08 »
Hi guys,
I'm back from the remapping (chipping) and have some answers. Unfortunately I can't produce a graph, since putting my car on the test bench would've set me back an extra 100€ and I found that quite expensive for just a graph. But I did ask how the graph would roughly look like with a 'before' and 'after' Torque line drawn on it, and they told me this:

The peak of the 'after' Torque would be higher than 'before' and would be around 400 Nm instead of 350. This 'after' peak would be around 1750-2000 rpm instead of the 'before' peak being around 2250-2500 rpm.
The 'after' Torque would also consistently be higher than 'before' Torque starting at 1000 rpm and both lines would converge again at about 3000 rpm. At 3000+ the lines would be the roughly the same, to avoid the increase in max horse power.
The exact parameters of the ECU (Electronic Control Unit) that were adjusted was a company secret (understandable) but they were willing to say that they modified throttle input/feedback, valve timings, turbo boost controller and fuel pump pressure.

Now, how does this translate in my driving experience: The throttle lag is gone. If I just lightly push in my throttle, the car responds immediately by accelerating a little bit. Acceleration greatly improved in the lower rev (<2000rpm) and slightly improved in the higher rev (>2000rpm). My 0-100 Km/h acceleration went from ~9.5 to ~7 seconds. I haven't done the 400m test before remapping, so I didn't test it afterwards either..

Fuel economy results will need to wait until my tank is empty :)

EDIT FYI: Didn't mention this before: The engine worked on is a 2199cc Turbo Diesel i-DTEC Honda engine.
i-DTEC is an acronym to say that it's a Diesel version of i-VTEC, and i-VTEC stands for intelligent-Variable Valve Timing and Lift Electronic Control. Japanese build great engines, but not great acronyms :)
« Last Edit: 02/04/2012 07:06:13 by Nizzle »

Geezer

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Re: What does "more torque" do to a car's performance?
« Reply #13 on: 02/04/2012 06:27:13 »
Should be interesting! I hope you have a lot of pre-tweaking fuel consumption data for comparison.
 
A problem with these things is that it's extremely difficult to get a real "apples with apples" comparison. My dark suspicion is that they have improved your acceleration at the expense of your fuel economy. You will like the increased acceleration, who wouldn't (I confess that I sometimes employ all 350 of my horses when Mrs G isn't on-board) but how will you know that is not influencing your assessment?

Nizzle

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Re: What does "more torque" do to a car's performance?
« Reply #14 on: 02/04/2012 06:49:00 »
Well, on my first full tank, I will do my utter best to reproduce driving style compared to before. I'm doing 150km daily on highway commute. I've done a test before remapping, always gearing up at 2000rpm with maximum use of cruise control in highest gear at speed limit of 120Km/h which gave me 985Km when the "fuel low" light came on, at which point I've used 55L of my 65L tank according to my car's manual.
So I'm hoping that on this tank, no accidents are happening on my route that would result in me being a lot more in traffic jams that would affect my fuel economy results. There will always be a difference in traffic circumstances and indeed you can't get an 'apples with apples' comparison because I haven't emptied an entire tank on a test bench before the remap, but hopefully I'll see a decrease in gas station visit frequency over the long haul. In my bank account history I can easily check how many gas station visits I did over the last years..

peppercorn

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Re: What does "more torque" do to a car's performance?
« Reply #15 on: 02/04/2012 12:35:27 »
Though I'm still somewhat doubtful that an increase in rated torque, whether or not the peak of the torque curve has closer to the more idealised rev-range for economical driving, has the capability to make for better fuel economy - L//100km (or mpg for us imperialists).

Geezer mentioned that Horsepower (or kW) is proportional to the instantaneous torque multiplied by RPM, so perhaps that's how the 'trick' works. If it's possible by adjusting valve timing to lower the revs at which a the engine's rated HP is available the max torque would be slightly higher (keeping the ratio the same).

Another possible avenue to investigate, Nizzle, is to see whether having a lower peaking torque curve might make your engine more suitable for 'pulse & glide' type driving. - I won;t go into the details of how the principle of P&G operation is known to improve F.E., but there is lots of info on it's (careful) use on the internet.

Lmnre

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Re: What does "more torque" do to a car's performance?
« Reply #16 on: 02/04/2012 13:16:21 »
Can changes in various operating characteristics make an engine more (or less) fuel efficient by increasing (or decreasing) the amount of torque produced for a certain amount of fuel consumed? I'm certain that the answer is that they can.

What I'm saying is that tweaking certain characteristics can increase the torque produced from the same amount of fuel consumed. I'm also thinking that, if such a thing was possible — all other things staying the same — the car makers would have probably incorporated it into their engines' computers.

So, what I'm saying is that there may be some adverse effects that the eco-chippers don't advertise — for example, higher chamber pressures (and thus, a greater possibility of a blown gasket), higher operating temperatures (and thus, faster deteriorating lubricant requiring more frequent oil changes), etc.

Nizzle

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Re: What does "more torque" do to a car's performance?
« Reply #17 on: 02/04/2012 13:25:28 »
Geezer mentioned that Horsepower (or kW) is proportional to the instantaneous torque multiplied by RPM,

Geezer also mentioned that for a given constant speed, your engine needs a given constant power output, so if my torque is higher, I need less revs for the same power output, and less revs means less fuel consumption, no?

Can changes in various operating characteristics make an engine more (or less) fuel efficient by increasing (or decreasing) the amount of torque produced for a certain amount of fuel consumed? I'm certain that the answer is that they can.

What I'm saying is that tweaking certain characteristics can increase the torque produced from the same amount of fuel consumed. I'm also thinking that, if such a thing was possible — all other things staying the same — the car makers would have probably incorporated it into their engines' computers.

So, what I'm saying is that there may be some adverse effects that the eco-chippers don't advertise — for example, higher chamber pressures (and thus, a greater possibility of a blown gasket), higher operating temperatures (and thus, faster deteriorating lubricant requiring more frequent oil changes), etc.

Yes perhaps, but they told me they are staying well within safety margins (which are maybe too big off-factory for dealing with drivers who abuse their engines) and they're giving a 3-year warranty on the engine with their product, so I'm not that worried. Also, my driving style is not about taking the engine to it's extremes...

« Last Edit: 02/04/2012 13:36:58 by Nizzle »

peppercorn

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Re: What does "more torque" do to a car's performance?
« Reply #18 on: 02/04/2012 16:48:56 »
Geezer mentioned that Horsepower (or kW) is proportional to the instantaneous torque multiplied by RPM,
Geezer also mentioned that for a given constant speed, your engine needs a given constant power output, so if my torque is higher, I need less revs for the same power output, and less revs means less fuel consumption, no?

Not necessarily.
Yes, many drivers claim to experience a 'gut feeling' that keeping an engine's revs low and short-shifting translates into improved F.E. but obviously there is a limit to which this is true - that is, there is a curve as revs get lower; one that ends at the 'cliff-edge' as the engine stalls.
It is wrong however to assume that engines are happiest in the lower part of their rev-range (only 10% above stall, say), especially when modern electronic control is factored in.  There are many influences on at what revs an engine is making the best work for the fuel consumed; breathing plays a part, as does thermal efficiency, as does atomisation, timing and a whole host of effects.
The best and easiest way to start to get attuned to your engine and work out under what conditions it will give you the best efficiencies is to look up its BSFC chart.

Geezer

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Re: What does "more torque" do to a car's performance?
« Reply #19 on: 02/04/2012 21:17:43 »
He he! Tis a trixy subject, and it has a lot to do with type of traffic.
 
The simplest case is cruising at constant speed on the level, and it's probably the only case that we can be reasonably confident about in terms of fuel economy. At constant speed the engine is running at constant speed (or should be!) and it is producing a certain amount of power which is also constant. The power is balanced by the resistances the vehicle has to overcome (otherwise the vehicle would be accelerating) like wind, rolling, losses in the transmission.
 
If the power output is constant, that means the engine is producing constant torque (because power is the product of speed and force - in this case a torque). So, the only way the torque could be any different under these conditions would be if the transmission ratio was different. Increasing the engine's maximum torque is obviously not going to make any difference in this particular case because the engine is only producing a fraction of the maximum.
 
If the dominant use case is cruising on motorways, I can't see how altering the torque is going to make much difference to the economy. However, if the vehicle does a lot of accelerating, I suppose it might, but the only reason I can think of is that it somehow allows the engine to operate more efficiently during acceleration - which is a clever trick if it works!
 

peppercorn

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Re: What does "more torque" do to a car's performance?
« Reply #20 on: 03/04/2012 16:04:00 »
If the dominant use case is cruising on motorways, I can't see how altering the torque is going to make much difference to the economy. However, if the vehicle does a lot of accelerating, I suppose it might, but the only reason I can think of is that it somehow allows the engine to operate more efficiently during acceleration - which is a clever trick if it works!

Three words:  Pulse and glide! 8D

Lmnre

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Re: What does "more torque" do to a car's performance?
« Reply #21 on: 03/04/2012 17:46:00 »
Hmm, let me describe my position in different terms.

At any given constant speed (and no wind, grade, etc), the thrust counters the drag. This thrust results from a torque applied to the road through the radius of the driving wheels. When the engine produces this torque with less fuel consumption, it results in better gas mileage; when the engine produces this torque with more fuel consumption, it results in worse gas mileage.

What's described by "eco-chipping" as increasing the torque (while keeping the fuel consumption constant) is, conversely, decreasing the fuel consumption (while keeping the torque constant).

Does this description make more sense?

Geezer

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Re: What does "more torque" do to a car's performance?
« Reply #22 on: 03/04/2012 19:37:19 »
Hmm, let me describe my position in different terms.

At any given constant speed (and no wind, grade, etc), the thrust counters the drag. This thrust results from a torque applied to the road through the radius of the driving wheels. When the engine produces this torque with less fuel consumption, it results in better gas mileage; when the engine produces this torque with more fuel consumption, it results in worse gas mileage.

What's described by "eco-chipping" as increasing the torque (while keeping the fuel consumption constant) is, conversely, decreasing the fuel consumption (while keeping the torque constant).

Does this description make more sense?

Yes, I think that's all correct. The problem is that torque is just another way of expressing power at a particular speed, so what we are really talking about here is reducing the fuel consumption rate for a particular amount of power.
 
When you express it those terms it sounds a lot more dodgy! (Which I think explains why they like to talk about torque - or am I being too cynical?)
 
The efficiency of an engine varies to some extent with its speed, but in this case, the speed has not changed, so that would not account for the improved economy. I'm not sure exactly what dials they have to play with to adjust things here, but I suspect they can only alter the fuel/air ratio. If that's true, the bit that I find contradictory is that, to increase torque, you usually have to increase the fuel per air which would take the economy in the wrong direction.
 
I rather think there is a high bullpucky coefficient on this one   :)
 

Nizzle

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Re: What does "more torque" do to a car's performance?
« Reply #23 on: 04/04/2012 06:48:03 »
The efficiency of an engine varies to some extent with its speed, but in this case, the speed has not changed, so that would not account for the improved economy. I'm not sure exactly what dials they have to play with to adjust things here, but I suspect they can only alter the fuel/air ratio. If that's true, the bit that I find contradictory is that, to increase torque, you usually have to increase the fuel per air which would take the economy in the wrong direction.

Could they perhaps achieve more torque not by altering fuel/air ratio but by altering fuel and air pressure in combination with using less fuel in the mixture?
PS: This is a sincere question, I don't know anything about the workings of an engine :-s

Geezer

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Re: What does "more torque" do to a car's performance?
« Reply #24 on: 04/04/2012 18:36:44 »
The efficiency of an engine varies to some extent with its speed, but in this case, the speed has not changed, so that would not account for the improved economy. I'm not sure exactly what dials they have to play with to adjust things here, but I suspect they can only alter the fuel/air ratio. If that's true, the bit that I find contradictory is that, to increase torque, you usually have to increase the fuel per air which would take the economy in the wrong direction.

Could they perhaps achieve more torque not by altering fuel/air ratio but by altering fuel and air pressure in combination with using less fuel in the mixture?
PS: This is a sincere question, I don't know anything about the workings of an engine :-s

There are not too many variables.  The throttle position (accelerator position) controls a flap that determines the mass of air that gets sucked into the engine, so what you are really controlling with your foot is the mass of air flowing through the engine.
 
The fuel system measures that mass and mixes the appropriate amount of fuel with it to achieve "proper" combustion. It has a little bit of wiggle room about the "proper" amount, but not much. If the mixture is not right, it can cause pollution problems and issues that can accelerate engine wear because of higher combustion temperatures.
 
They can't alter pressures or combustion chamber design without mechanically altering the combustion chambers. They might be able to do something with valve timing, but only if the engine has a mechanism to do that, so I think they can only be modifying the fuel/air ratio “map”.

The vehicle manufacturer would have extensive data on the mapping they decided on, and I'd be surprised if their emphasis was not on economy which is why I'm a bit skeptical, but maybe the “chipper” knows something they didn't know, or maybe they are just making some tradeoffs that take things a bit closer to boundary conditions than the manufacturer was prepared to.
 
EDIT: I forgot about timing. They can probably adjust the ignition timing too so that the fuel/air mixture starts to burn a bit earlier or later, and that can also influence torque. Again, they have to be careful that they don't create other problems if they deviate too much from the norm.
 
The mixture takes time to burn, so the trick is to start it burning so that the heat expands the gases in a way that extracts the maximum amount of work as they push on the piston, and because the engine speed is variable, the timing of the spark has to be adjusted. There are probably some compromises made to accomodate variations in fuel and other conditions, so that might give them a bit more room to optimize around a less general case.
« Last Edit: 04/04/2012 20:25:25 by Geezer »

 

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