Articles tagged with: Accuracy

Car profile tips part 2 : using gear speeds instead of gear ratios

on Sunday, 05 July 2015. Posted in Using PerfExpert

How to use the new Gearbox feature to set gear specification without knowing their ratio

Car profile tips part 2 : using gear speeds instead of gear ratios

Since PerfExpert for Android version 1.7.0 there is a new Gearbox screen that is intended to help you filling your car profile parameters when you are not able to find any info about your gearbox ratios and your final drive ratio. This provide another way to set the gearbox specifications allowing PerfExpert to calculate the engine rev without any connection to the car. As you already know, PerfExpert calculates the engine rev from the car speed, so why not simply telling to PerfExpert what is the speed of the car when the engine is at a specific rpm value on a given gear ?

Here are some explanation about how to use this feature. Notes that when you choose to edit gears by specifying their related car speed, the Final Drive Ratio parameter and Gear Ratio parameter values are completely ignored by PerfExpert when calculating engine rev.

Case 1 : you know the car speed at 1000rpm

If you know accurately the car speed at 1000 rpm for each gear then you can choose "Edit by speed @ 1000 rpm" and enter the right values. Usually, you will find the speed at 1000 rpm information for your car in repair manuals or on car sheet websites.

Case 2 : you don't know the car speed at 1000rpm

If you can't find neither the speed at 1000 rpm nor the gear ratio value, then you can use a GPS to help you find the right information. The purpose is to measure the exact speed of your car at either 2000 rpm (better for diesel engine) or 3000 rpm (better for gasoline engine) on the given gear.
Let's say we have a gasoline engine and we want to enter the 2nd gear info in PerfExpert. To do so you will have to drive the car at 3000 rpm on the 2nd gear and to stabilize the car speed in order the GPS can provide a fixed speed value for that engine rev. The more accurate the GPS speed will be, the more accurate the calculated engine rev will be. Once you managed to get a fixed speed from the GPS :

  • Go in the Gearbox screen
  • Select "Edit by Speed @ 3000rpm"
  • Touch the 2nd gear speed field. A checkmark button will appear at the top of the screen.
  • Enter the GPS speed value for the 2nd gear
  • Validate this value by touching the "checkmark" button at the top of the screen
  • Validate the new gearbox infos by touching the "OK" button at the top of the screen

Edit gear speed

This technique is an alternative way to have your car profile filled if you can't find info about your car in any documentation. When gear ratio or speed at 1000 rpm values are available, they will give more reliable results than using this GPS technique.

Highlight your PerfExpert vs Chassis Dyno comparison

on Monday, 22 June 2015. Posted in Announcements

Send us your comparisons to better convince the most skeptical ones about PerfExpert accuracy

Highlight your PerfExpert vs Chassis Dyno comparison

Most people find it hard to believe that a smartphone application can measure power and torque with an accuracy very close to chassis dynos, without any connection to the car or without any external measuring equipment. They generally think of a hoax, because they cannot imagine the real potential of the modern phones sensors, especially when they are combined with powerful algorithms and calculations. Thus, providing them the proof with "PerfExpert vs Chassis Dyno" comparisons seems to be the solution.

What could be better than seeing this proof brought by other car enthusiasts who tested PerfExpert by themselves?

If you carried out this kind of tests you can contact us to transmit us your results, by sending us the following elements :

  • A copy of the full report of the chassis dyno result, in other words, the result sheets, perfectly readable, scanned or photographed
  • An Image export of PerfExpert measurement curves, and, if possible, with two PerfExpert tests carried out under the same conditions (same road, same direction, same starting point, same day)
  • The links towards your tests on the Web PerfExpert Network
  • And for the fun, if you agree, a beautiful picture of your car, outside and/or on the chassis dyno! :) We will hide the license plates if they appear.

We will gather them in our Google + collection of PerfExpert vs Chassis Dyno comparisons.

Speaking about PerfExpert around you and showing that it is a reliable application when it is correctly used allows us to keep on improving it and creating new features! As a user, you now know how to answer those who ask you about the application's accuracy and reliability compared to chassis dyno's. In fact, this is often the first question people ask when they discover that the PerfExpert application allows them to measure your car engine’s power and torque using only your smartphone!

Here is an comparison example from our collection :

PerfExpert Car Dyno=> Power : 301cv / Torque : 370Nm

Cartec Chassis Dyno => Power : 300.5cv / Torque : 371Nm

Nissan 350Z

Nissan 350Z chassi dyno result

Nissan 350Z PFX result 


Car profile tips part 1 : weigh your car for more accurate dyno results

on Friday, 03 October 2014. Posted in Using PerfExpert

How to better fill your car profile to obtain realistic results

Car profile tips part 1 : weigh your car for more accurate dyno results

Although PerfExpert can be used to evaluate the mechanical changes of a car by making comparison of measurements before and after modification, PerfExpert can also be used to just check the actual engine horsepower realistically. To do so, not only you must ensure that you perform your tests in the required conditions, but you must also ensure that the car profile parameters you entered are right.

The weight of your car is one of the most important data PerfExpert takes into account when computing dyno test results, as it has a direct effect on the displayed horsepower and torque. In this blog post, we will see how to fill and manage both the 'Car weight' and the 'Additional weight' parameters in the car profile, and how to weigh your car for more accurate dyno results. The other car profile parameters will be covered in future blog posts.

That car used as example here is a Toyota GT86, checkout its PerfExpert Network page here.

Use the 'Car weight' parameter as a contant value

The best way to use this parameter is to consider it's a constant value. That mean you will not alter this value each time you have to test your car.

You don't know exactly how much your car weigh

Ok, don't worry about that, you will be able to start using PerfExpert by considering the advertised curb weight of your car as the 'Car weight' parameter, and later update your test results after weighing up the car.

The curb weight is the "total weight of a vehicle with standard equipment, all necessary operating consumables (e.g., motor oil and coolant), a full tank of fuel, while not loaded with either passengers or cargo" as explained in the Wikipedia definition. This value is provided by the car manufacturer and can be found on the car manual, on car database like, and on the PerfExpert support forum, in the dedicated section.

As mentioned in the Wikipedia article, some countries may have slightly different definitions considering that the fuel tank is filled at 90% for example, or that this weight also include a 75Kg passenger. Also, some manufacturer just advertise a base curb weight, that mean the curb weight of the vehicle with only the base trim features installed, not the optional equipment (sunroof for example), as explained in this interesting post

As you can see, although the advertised curb weight is a good value to start with, it's still uncertain and this affects your test result accuracy. So if you want to get the actual engine horsepower realistically, you will need to weigh your car at some point. Then you will be able to modify the 'car weight' on each of your previously performed test, so PerfExpert can re-compute the horsepower/torque and update them.

You have the opportunity to weigh your car

That's the way to go the get more accurate results ! This can be done at a motorsport garage/club using specific weighing scales.

Black Toyota GT86 weighing

You must ensure that you meet certain conditions when weighing your car :

  • The car must not be loaded with either passengers or cargo (not even the driver)
  • All liquids must be level (engine oil, coolant, brake fluid...)
  • Fuel tank must be full

In other words your car must be in the conditions of a "curb weighing" considering the first definition that we saw above.

Black Toyota GT86 weighing

The measured weight must be entered in the PerfExpert car profile as the 'Car weight' and must not be altered until the car is modified.

Toyota GT86 weight

Here we get 1238Kg for a french 2013 Toyota GT86 that has the following modification :

  • Milltek catback resonated exhaust
  • Cosworth air filter in OEM air filter box

Use the 'Additional weight' parameter as a variable value

Each time you will perform some dyno test, you will have to adjust the total weight of the car at the time of the measurement. To do so, you just have to modify the 'Additional weight' accordingly.

Additional weight = (passengers weight) + (cargos weight) - (missing fuel weight)

Here we are considering that the car has not been modified since the time you entered the 'Car weight' parameter, so no need to alter it. Also we are considering that the engine oil, coolant and other fluids are level.

You have to calculate the missing fuel weight from the fuel tank capacity, the actual amount of fuel at the time of the test and the fuel weight per liter :

  • Gasoline : 0.755 Kg / L
  • Diesel : 0.845 Kg / L

For example, if at the time of the test of a gasoline car that have a fuel tank capacity of 50 Liters, we have inside the car :

  • The driver (75Kg)
  • A passenger (82Kg)
  • A tool box in the boot (15Kg)
  • Fuel tank filled at 45% (so it misses 55% of fuel to fill the fuel tank)

Then Additional weight = 75 + 82 + 15 - (55%*50*0.755) = 151Kg

Hope all these tips will help you get more accurate results !