The Myths And Truths Of Remapping

Rolling Roads: THE FACTS

Rolling roads are a way to measure the power of a vehicle. However, they can also lead to many an unhappy and confused car owner as results can often be misread due to a general lack of understanding of the limitations, drawbacks and also benefits of a rolling road.

There are a few fundamental things you should know about rolling roads:

  • It is impossible for a rolling road to simulate real world driving. Rolling roads provide linear load on the engine and do so with a slow pull from low RPM’s to redline. It can take up to 45 seconds to reach redline. This amount of time and constant load on an engine and turbo charger will inevitably raise intake temperatures well beyond what the real world driving will see.

  • Raised intake temperatures will cause the ECU to factor the boost / fuel / timing maps to reduce load, thus limiting power. This is a protection feature.

  • It is very common for a car to have less rolling road performance and yet maintain strong power on the tarmac. This can be attributed to several factors.

  • The fan we usually see in front of the vehicle when a vehicle is on the rollers is providing a linear flow of air (constant flow/volume/temp), usually to a small portion of the frontal area of the vehicle. If we were to compare this to real world conditions, we can prove airflow is proportionately increased as speed is increased. This isn't replicated with the airflow on a dyno. This causes the air intake temperature to be well outside of what we would see if we were to log temperature on the road. The higher these temperatures get, the lower power output will be. So from this we can make some assumption that a car will probably make more power on the road than the dyno.

  • The final figure will also be variable with weather. Ever noticed on a cool, damp evening your car seems faster??

 

HEAT SOAK

 

A term used when an engine doesn't get adequate cooling for the given running conditions and the ECU will be forced to compensate for the additional heat. When a car suffers from heat-soak the ECU will typically go into an Exhaust Gas Temperature protection mode; lowering the requested load and increasing the amount of fuel in attempt to cool things down, this results in the curve tailing off much quicker than expected and a lower than realistic power output.

  • The majority of rolling roads will load a vehicle up during a power run in a certain way, this can vastly effect how the car ‘behaves’ on the rolling road as the ECUs are load based. All requests to the engine are calculated based on the feedback the ECU has from the engine and the load it’s under.

  • This doesn't even take into account any potential issues that could be inherent with a car, the amount of heat already in the car before it goes on the rollers, or any inconsistencies between operators and rolling road calibration. For Example: vehicle weight, number of cylinders, transmission type, air temp, air pressure. All factors not entered into the dyno software correctly that can lead to BS figures.

  • Wheel and flywheel figures can be a source of confusion, and there’s a danger of back-calculating flywheel figures from a chassis dyno. Power at the wheels is more meaningful and fairly accurate so long as the ambient and intake temps are reasonable. Certain rolling roads calculate force applied at the rollers, everything from there on is a mathematical equation and as such don’t necessarily give you accurate figures.

  • One of the biggest mistakes people make is to take a figure from a Rolling Road as gospel. There are so many varying factors between different dynos that can affect the output, (as mentioned above), that can differentiate vastly from one rolling road to the next. Realistically, a Rolling road can be a great tool to show differences from the fitment of additional hardware, but in the guise of a rolling road ‘shoot-out’ for a one off reading they are a waste of time.

“A figure or power curve only shows what the car is doing on that dyno, on that day, in those conditions.”

  • Using a Rolling Road to show the difference between cars or show the increase from software can also be unrealistic without correct preparation. If you have two identical cars running the same quality fuel, tyre pressures, etc. you can still have a variable within the ECU due to differing driving styles and conditions the cars see. One car might have been used much more aggressively than the other and have a much larger correctional factor due to adaptation from excessive heat. This can vastly affect the power output of a vehicle. Something else to be aware of is after programming an ECU the car will take a certain period of driving time to adapt (short/long term fuel trim), this period of time is dependent on driving style and conditions.

What is important is a road test and inspection of the vehicle before it's flashed. A full check over of the vehicle to see if there are any issues that need addressing prior to software being installed.

 

PEAK FIGURES

  • The peak numbers you get on a rolling road are typically referred to as ‘Pub Talk’ numbers; who has the most power and torque! In reality the Peak numbers are largely irrelevant; it's the power/torque throughout the rev range and the power delivery that's important, the peak number gives very little indication to how capable a vehicle is or how well it drives. Unfortunately there’s a lack of understanding in the industry and still a requirement to quote peak figures?

At the end of the day peak power and torque figures are all pub talk and mean very little in real world conditions. Peak figures don't give you any indication of drivability or even a true indication of increased performance as they ignore the power/torque curve and can’t tell you how smooth, powerful and efficient the power is delivered.

  • The general consensus is the higher the number the better, numbers sell. A 300hp car sounds much better than a 280hp car! But in reality what can you tell by these numbers?

  • First of all, quoted power and torque numbers are peak figures, they are the highest seen figures on a power or torque curve. They tell you what power and torque a vehicle is making on that dyno but those figures are really only useful for bragging rights. For a true indication of how a vehicle will feel and where the benefits of tuning can be seen you need to assess the power and torque curves, In the below example there are three power curves,

  • Purple is stock

  • Red is stage 1

  • Dashed blue line is hypothetical

 

  • on paper the dashed blue line makes the most power as it peaks nearly 10bhp higher.

  • However from 2400rpm through to 6000rpm the red curve makes a lot more power.

  • At 3500rpm the red curve is 50bhp more than the dashed blue curve.

  • On the road, a car running the red curve (with a lower power output) would be a much quicker car.

This is a good example of how a peak number can be very deceptive and not tell the full story. You can see the difference in the area under the curves and how much more the red curve has gained throughout the rev range in comparison to the dashed blue curve

We don’t go chasing peak numbers but getting the balance between power and drivability is key.

Whilst an understanding of peak figures and power under the curve is important, it’s just as important to understand that rolling road results can and do vary and aren’t always a true representation of what a car will do in the real world.

I HOPE THIS WILL MAKE SENSE, AND YET AGAIN, TAKE OUT MORE LIES FROM THE INTERNET FORUMS.

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