Keep in mind, its ONLY hp that determines the acceleration potential. torque is just a number. without an RPM attached to it, its meaningless.


so, if both cars have the same hp, they will accelerate at the same rate at any same speed range. the generalization is that with a greater torque value, you get a broader HP curve, so possibly better acceleration post shift.
acceleration = power/ (mass x velocity) so, acceleration is proportional to power.

 

Sorry to go all OT on this, but is this the general summary of this relationship that I've been looking for?

I've always (totally mis-)understood that there is some relationship between hp and torque, but I've never seen a good analogy. Perhaps the fact that AM likes to provide tune variations to otherwise identical cars makes for a good place to understand the damn thing.

So the higher hp from the same engine in virtually the same car gives you what? Faster 0 - 60? I've always associated higher torque with faster acceleration but I know I'm wrong.

 

dont worry, its the most misunderstood concept not only in automotive, but in physics in general. the Power vs force debate!

in a nutshell. torque, which is just rotational force, is what causes the acceleration...... at any speed. BUT, what almost everyone forgets, is that its not engine torque, its the torque at the wheels that is multiplied through the gear box...... so, in a nutshell, because torque is a component of HP, and HP also incorporates speed or RPM, it just has MORE information . its better to use, because it tells you more. So, you either use HP to compare two cars, or you go through all the calculations of engine torque, to get what the actual accelerative force is at the wheels THROUGH the gear box and what the force is at the tires at any vehicle speed. Why not just see what the two car's HP is at any speed and which ever has more, will accelerate faster.

so, if you have more HP and can always keep your car in that greater HP range, you will be quicker, faster, etc. this is the reason for close ratio gears, to keep you in the max hp range when you are accelerating. 7speeds do a great job of this. a 12 cylinder engine, generally has a wide HP range , so each gear will and can be in this narrow range to maximize the HP it can use. regardless of what he engine torque value is, its all about the HP.

Now, if you want to accelerate from idle to some speed, and have it feel fast, (that torquey feeling) engines with greater torque will do this, BUT, if you use the right gear, the engine torque value becomes a non issue /factor, and HP is the easier comparative value.

the net net is look at the engine HP curve. If you keep the RPM in that range and you have more average HP than another car, you will always out accelerate, at any speed, on any drag strip, out of any corner, regardless of its Max torque engine values.

 

Thanks.
And this points to a larger issue. Who gives a crap about max any of this? I realize that they have to give some number and Max is better than something random, but from the hp and torque graphs I've seen, a car with a Max hp of X can suck to drive and feel less quick than another car with a Max hp of X-Y.

What I want is a metric for the feeling of power. Don't really care about the actual max since on the streets, I just don't drive like that (and pretty much no one else does).

So is it fair to say that for actual street driving, where you are looking for power from 1000rpm, more torque will provide a greater feeling of power than more hp?

 

yes, the around town feeling will be as you say. pure acceleration is in the max HP range and that is in the high RPM range. but that feeling you speak of around down is enhanced with greater engine torque numbers.

You got it!

 

Three words: Variable Valve Timing.

The new v12 enging is totally different than the last in that it finally now has variable valve timing. that's why the old V12s and new V12s differ in torque.

The reason the new DB9 (aka Virage 2.0) has same torque but much less power is Aston is up to their usual sandbagging tricks by intentionally detuning it, so they give you all the bottom end but on the top end they just intentional taper off the power to a much lower level. Vanquish also has some more free flowing intake & exhaust side mods.

Basically they identical otherwise

 

As stated earlier, HP and torque values without their associated RPM values don't tell the whole story. Although both V12 engines have the same peak (maximum) torque (457 lb-ft at 5500 RPM) at the same RPM, their peak HP values occur at different RPM values. The DB9 develops 510 HP @ 6500 RPM while the Vanquish develops 565 HP @ 6750 RPM - 250 RPM higher; according to the AM website.
The calculated DB9 torque value at 6500 RPM is 412 lb-ft and the calculated Vanquish torque value at 6750 RPM is 440 lb-ft; both values below the maximum.
Without seeing the actual engine performance cures, one can make the inference that the Vanquish engine has a slightly "broader and flatter" torque curve to go along with its increased HP-most likely accomplished by software adjustments to ignition and valve timing and other works of "black magic," as mentioned by others.

 

I have been told that whereas the DB9 & DBS had physical differences on the intake side (one optimized for torque, one for HP) the New Vanquish and the New DB9 are the same physically, only difference being software.

 

Its not the flatter torque curve. its actually a torque cuve that is falling less. the flatter HP curve, is due to a falling torque curve, and the misnomer that a "flatter torque curve" is somehow better, is just that. torque in ft-lbs is always falling and falling fast after 5250rpm. you just want it to fall less.
the reason that the HP curves are better, and greater, is generally do to the engine being able to breath better at the higher RPM. this is due to cam timing, cams, and intake differences (if any) and ECU control (air/fuel, spark timing).

 

Sorry, but you've got it *** backwards. A flat torque curve is good, since it means HP is rising with rpm. A flat HP curve is the result of a falling torque curve, not a flat one.

 

Sorry, I fixed the point I was trying to make. again, torque curves all are falling dramatically after 5250 . what you want is a torque curve that is falling less, or falling at a rate of 1 for 1. (kind of falling at a 45degree angle) this means that HP is flat. that's what you want.


especially in our engines , where the operational range for max acceleration is well after torque starts to fall. Its the flat HP curve you want, or one that allows the engine to operate in the highest level of HP possible. (or highest average HP over one gear range )