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 ?
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.