PerfExpert includes a Gearbox screen that helps you fill in your car profile parameters when you are not able to find any info about your gearbox ratios and your final drive ratio. This provides another way to set the gearbox specifications, allowing PerfExpert to calculate the engine RPM without any connection to the car. As you already know, PerfExpert calculates the engine RPM from the car speed, so why not simply tell PerfExpert what the speed of the car is when the engine is at a specific RPM value on a given gear?
Here are some explanations about how to use this feature. Note that when you choose to edit gears by specifying their related car speed, the Final Drive Ratio and the Gear Ratio values are completely ignored by PerfExpert when calculating engine rpm.
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 spec websites.
Case 2 : you don't know the car speed at 1000rpm
If you can't find either the speed at 1000 rpm or the gear ratio values, 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 engines) or 3000 rpm (better for gasoline engines) on a 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 in 2nd gear and stabilize the car speed so that the GPS can provide a fixed speed value for that engine rpm. The more accurate the GPS speed is, the more accurate the calculated engine rpm will be. Once you have managed to get a fixed speed from the GPS:
- Go to the Gearbox screen
- Select "Edit by Speed @ 3000 rpm"
- 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 info by touching the "OK" button at the top of the screen
This technique is an alternative way to have your car profile filled in 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.