The Perfect Rally engine management.

Turbo restrictor tuning - the difference between getting it wrong & getting it optimized. All of the functions & development that make Life Racing engine management the best choice for circuit cars also make them ideal for Rally applications with a couple of extra benefits such as restrictor boost control & 4wd center diff control.

The mandated turbo restrictors for rally use present a special challenge to extract the best power & reliability. The dyno graph clearly illustrates this with a 80hp gain at 7000rpm just by optimizing the boost control. Life Racing's extensive involvement with such setups means their boost control offers extra functionality utilising extra sensors into the boost control system to automatically optimise the ideal boost target. This results in more power & better life from the turbo & engine.

Reading dyno Graphs – what is Power & Torque?

 There are many urban myths out there regarding what power & torque are which cause confusion when trying to take meaning from dyno graphs. We often hear comments like “its all about the torque” or “torque wins races” and  “I need more torque, the horse power is ok” as if the engine makes torque lower in the rpm & then suddenly switches to horsepower at high rpm.

Lets put some of this confusion to rest by having a look at what torque & power actually are.

Torque is the tendency of a force to rotate an object about an axis.

Ok what is a force? A force is any interaction that, when unopposed, will change the motion of an object. In other words, a force can cause an object with mass to accelerate.

One way to visualize force & torque is when you undo a bolt with a spanner you apply a force to the end of the spanner to create a torque on the bolt to undo it. In an engines case the force is created by the heat/pressure on the piston to create a torque at the crank shaft.

Both force & torque are a momentary thing that do not include time. Ie the rate that they are delivered.

So now let’s take a look at what power is

Themechanical horsepower is 550 foot pounds per second (or 33 000 foot pounds per minute). The formula for it is;

So power is torque multiplied by the engine rpm divided by a constant.

The constant 5252 is thevalue of (33,000 ft·lbf/min)/(2? rad/rev) to bring the units right when dealing with an rpm value.

The key thing is that it is a "delivery rate of torque".

So if an engine makes say 100lbft at 4000rpm it will be making 76.16hp. And if it makes 76.16hp at 4000rpm it will be making 100lbft of torque. It does not matter how big or small the engine is, or if it is petrol or diesel, 4-stoke otto, 2-stroke, rotary or electric.

The effects of gearing

This is where things get interesting. For the purpose of making the numbers simpler & clearer we will ignore the losses through the drivetrain (gearbox, diff etc).

We know that when we shift from a higher gear to a lower one the engine rpm increases for the same vehicle speed. The lower gearbox gear multiplies the engine rpm. The diff ratio does a similar thing. However, the gearing also multiplies the engine torque.

For our engine above, if it were operating at 4000rpm making its 100lbft of torque in a 4^th gear of say 1-to-1 and a 2-to-1 diff ratio the driving wheels/tyres would spin at 2000rpm and the torque at the wheels/tyres would be 200lbft.

Lets say we changed the diff ratio to be 4-to-1 and operated our engine at 4000rpm again. Now the wheels are only spinning at 1000rpm but the torque at the wheels has increased to 400lbft.

So what happens to the power in the above examples? In the first example of a 1-to-1 4^th gear & a 2-to-1 diff ratio and the engine operated at 4000rpm the torque at the wheels is 200lbft and the rpm at the wheels is 2000rpm so the power is 76.16hp at the wheels.

And in the second example the torque is 400lbft at the wheels & the rpm at the wheels is 1000rpm resulting in the power at the wheels being 76.16hp.

We can see that the torque becomes very dependent on what gearing is used, where as power is the same because it is the delivery rate of torque & takes rpm into account. So when making comparisons power is a much more useful figure to be working with.

The key thing to be looking at is the area under the power curve.

Two engines may have the same peak power figure but if one has more power at the bottom end &/or mid range of its operating range then it will be faster - period. The torque will be what it will be for this to occur & isn’t really relevant except to know how strong a clutch to fit.

An example

In the two engines below, which one would be faster? Both have the same peak torque value of a bit over 300lbft but engine-B appears to have more area under the torque curve so it would be intuitive to think it is faster?

Here is the resulting POWER curves for the above engines;

There is no doubt that engine-A would be significantly faster than engine-B even though it makes the same peak torque. It does this because the makes that peak torque at twice the rpm resulting in twice the power (the torque is delivered at a higher rate).

If we wanted to improve engine-A we could do modifications to lift the power at 7000rpm (ie bottom end of the power curve) or at 8500rpm (mid range of the power curve).

The above example isn’t to say that a high rpm engine is the only solution (there is more than one way to flip a pancake), but it illustrates the concept very well.

Taking your car to the Dyno

 We have prepared some help full advice regarding having your pride & joy dyno tuned.

Firstly how does the AVR Dynapack dyno work? It is a chassis dynometer known as a hub dyno. What this means is that rather than the car driving a set of rollers with its tyres (with all of the risks & inconsistencies) the wheels are removed & a set of adaptors are bolted up in their place. The dynos control pods then slide onto these adapters, one pod for each driving wheel - our dyno can accommodate 2wd or 4wd vehicles.

What then takes place to tune the car? Through its hydraulic control system the Dynapack can operate in a number of ways. A large proportion of the tuning involves what is called "steady state". Here the engine is held at a constant engine rpm while the dyno operator varies the load on the engine via the throttle. This allows the tuner to tune each point or site in the ecu maps for optimum performance/reliability. The other part of the tuning process involves what is known as "ramp runs" or "power runs". This involves operating the engine from a fixed starting point (say 2000rpm) to its redline under full throttle. The dyno automatically controls the run under a fixed rpm increase rate. This is what is used to generate the dyno graphs everyone is familia with. If the car is turbo charged the tuner will work thier way up from the lowest boost setting to the highest tuning each level.

So what is exactly "tuned" anyway? The two principle parameters are the fuel mixtures & ignition timing. To measure & assess the fuel mixtures a wideband Lambda sensor/unit is used. These are also known as mixture meters or oxygen sensors (O2). Via the ecu tables/maps the tuner can then vary the amount of fuel delivered to the engine & assess the effect on performance. A similar thing takes place with the ignition timing but this time some knock detection equipment is used to ensure that the engine does not operated under dangerous detonation conditions. In both cases the dyno is used to measure changes in power to optimize the tuning. Depending on your particular car other aspects that will be tuned are the boost control, injector timing, variable valve timing, drive by wire throttle setup, acceleration fuel control, etc

So what are the risks? The Dynapack chassis dyno is the safest type of chassis dyno to have your car on. There is a misconception that a dyno is harder on the vehicle than the race track. A power run is set at around the same rate of rpm increase as your car winding up to its redline in 4th gear with breaks in between, where as on the track it is punished for laps on end, so in this sense it is easier on things. It is also under controlled conditions & obviously the vehicle is not moving. The AVR dyno has a powerful cooling fan setup that ensures cooling air for the engine & drivetrain.

What do I need to do to prepare for the dyno?

>< The first thing to consider is that anything that causes a stoppage or interruption to the tuning process will cost you more money in dyno time. So prepare for a dyno tune in the same way you would prepare for a competition event. Make sure there are no fluid leaks, the boost control is working properly & there are no mechanical issues with the car, its engine or drivetrain. 

><  Bring enough fuel of the type that is intended to be used. Usually around 40L would cover it (for ethanol brews bring more!)

>< Ensure you bring any keys for wheel locking nuts and the wheel studs are not striped or damaged.

>< For the measurement of the fuel mixture a Wideband lambda sensor is used. This requires a M18mm x 1.5 threaded boss to be present in the exhaust system. In the case of turbo charged vehicles this is to be after the turbo. It is also important that there are no leaks in the exhaust system prior to or around the sensor as this will make the readings inaccurate. Let us know prior to the tune if your vehicle does not have a suitable boss & we can supply or supply & fit a suitable boss.

>< Bring your vid cam!