Torquing about power

Auto racing began five minutes after the second car was built.

- Henry Ford -

---

---

A few weeks ago, I decided to get the engine and transmission on my four wheel drive tuned. I wrote about it here if you're interested in taking a read and learning the reasons why and what's involved. I've been thinking about doing this for a while and finally decided I'd get it done because I could think of no good reasons why not to, and many good reasons why I should.

I promised I'd put together this post to talk about the result of the tune and, more specifically, the increase in performance.

Torque

The force that acts upon a pivot point with the aid of a lever arm is called torque That's physics. In respect of a vehicle, torque refers to the force which acts upon a vehicle's drive-shaft as it rotates.

It is measured in newton-meters (Nm) and is represented as Force (N) x Lever Arm (m). It can be measured in pound-feet (lb-ft) also, but mine is in Nm so let's stay with that. It can also be called rotational force which is directly linked to that drive-shaft thing mentioned above. Force (N) accelerates things in a straight line and a vehicle's engine torque (and its power) relates directly to the speed in which this force acts, and therefore both torque and power are determined by engine speed.

I hope you're still with me, but if you're asleep, don't let me wake you.

The best use of a combustion engine, with respect to torque, is high torque at low engine speeds (revolutions or revs). Also, that torque should come on or be applied, over the maximum range of the engine speed. This provides better drivability as it leaves the shortest delay between pressing the throttle and the engine responding to it, that's called torque demand.

A lot of torque (high torque) coming in early (at low revs), delivers a lot of certainty to the driver and a better feel to the vehicle; drivability. It also provides rapid forward-motion throughout the rev-range. This is one aspect that was tuned into my vehicle.

Torque: Before and after

• Pre-tune: 601Nm at 2,198 rpm
• Post-tune: 773 Nm at 1,868 rpm
• Percentage gain: 28.62%

Below you can see the torque curve of my vehicle. You'll see that, post-tune, the torque comes in at much lower engine revs (earlier) and is stronger for longer. The blue line shows the after-tune torque. This means the vehicle will be more responsive (sharper and punchier) all the way through the rev-range which makes it more responsive and better to drive. It'll also make a massive difference when I'm towing and off-roading as the vehicle will respond with greater speed and accuracy on torque demand. (The pressing of the throttle pedal).

More torque also relates to better economy if the vehicle is driven smoothly which is how I drive. I'll not have to push the vehicle as hard but will get better performance earlier in the rev range and all the way through it. That basically means less throttle input and that means less fuel goes in. With this increase in torque I should see a marked difference in fuel (diesel) consumption and that means dollar-savings at the pump.

Power

Engine power is measured in kilowatts (kW) which is derived from the formula: power = force x velocity. A single watt (W) stands for one newton-meter per second; it's basically the energy exchanged in a set period of time. Remember the old horsepower (HP) measurement? One HP literally is the power needed to raise 33,000 pounds to a height of one exactly foot in one exactly minute. Simple, but complicated. Anyway, kW is used now.

For performance in a vehicle high torque and high power need to combine.

Power: Before and after

• Pre-tune: 161.7kW at 3,626 rpm
• Post-tune: 176.2kW at 3,626 rpm
• Percentage gain: 8.96%

Below you'll see the old and new power curve and notice the new power curve rises more steeply (earlier) to greater power and stays higher all the way to high revs (rpm). You can see it peaks at 3,626 rpm which, for my twin-turbo V8 vehicle with a six-speed transmission is very high revs. Interestingly though, you can see the power stays well above the old power output curve all the way through to 160kph. That's the gain in power after the tune.

I mention in my last post linked above that a dynamometer (dyno) is used to tune engines, along with a computer and software.

The dyno is a thing the vehicle is driven up onto, rollers basically, where the vehicle is tethered and then run throughout its rev-range and at high speeds without actually going anywhere. As you can see on the graph above, mine was run hard to 160kph. It's faster than I drive on the roads, although when overtaking I've had it up there. With the increased power and torque now it'll get there a lot faster.

This engine and transmission tune will make my vehicle feel a lot better and actually drive a lot better.

I noticed a difference as soon as I began to drive away. The transmission changes gears later and a lot faster in the cog-swap, which keeps revs and power up to maximise efficiency, and makes it sharper. The additional torque and power means I'll use less throttle (torque demand) to get the vehicle to speed, and operate throughout the rev-range, and it's more responsive to the throttle as the lag has been taken out of it. Basically, it means I can drive the vehicle easier but get far more performance from it I got before which equates to fuel savings.

Of course, if (let's just say when), I put my foot into it the vehicle will giddy the fuck up a lot more responsively meaning much faster acceleration all the way to maximum output - This will suck down the fuel though of course, and it's not how I usually drive. It will come in handy when in emergency situations or when overtaking the big vehicles (road trains) which are commonplace in Australia.

I've not had a chance to give it a good run yet and it'll take a while to gather all the data anyway as I'll need to go through low and high-speed running, normal and hard acceleration, towing and off-roading before I get a true picture. Initially though it's bloody brilliant and the mix of hugely increased torque and the power increase together with the transmission tweaks has transformed my vehicle. I feel pretty damned good about it.

---

If you have any questions please feel free to ask but remember I'm not very smart and don't know much about things at all - I'm just a knuckle...I'll answer as best I can though.