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.

Leave a comment

Please login to leave a comment. Optional login below.