Gear ratio  


quick question I have my Clayton setup for inertia only I’ve set it up by using a car that has been on my friends dyno we set my moi so the car makes the same power etc in my friends , but I find if I set the gear ratio and do my pull in 3rd gear the power figure comes out spot on , but if I sett my gear ratio to 4th gear it makes nearly 50hp more any ideas ? 

Posted : 26/03/2019 8:40 pm

the best way to test a car and get the close flywheel hp readings, is to test using the ratio 1:1 to engine, if you try another gear, it's very likely you get more or less hp. for Wheel hp readings, doesnt matter what gear you use.

Posted : 27/03/2019 11:59 pm

The MOI must be wrong.

You will get different wheel readings due to friction/speed in different gears.  You need to set the MOI so that you get the same flywheel power in two different gears


Posted : 28/03/2019 3:00 pm

Hi I’ve been playing with this today like you say adjust the moi to get the same power in different gears , this is impossible as which ever way I change my moi (up or down ) it just increases or decreases the power reading in. It’s gears 

Posted : 10/05/2019 11:33 pm
Dyno Wizard Moderator

The gearbox is changing the torque and HP is just a function of Torque and RPM.
You need to set it up so MOI is correct in the gear closest to 1:1 Then gear ratio in yourdyno should be close to final drive ratio when you do rpm calibration. Wont be exactly the same since you have a wheel size changing it, but it will be close.

MOI will change with each car, But once you have one dialed in with 1:1 gear ratio its close enough. If you wanted some more accuracy then could have a value for FWD and RWD cars.
At the end of the day your not after a dyno that reads bang on accurate HP, If you did youd get a bench dyno. You want one thats close enough in reading HP but mostly gives a repetable run/readings so you can see what difference changes to the tune make.

Posted : 11/05/2019 5:01 am
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