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Effect of final drive and gear ratios on dyno output
Posted: May 26th, 2007, 4:28 pm
by smckeown
Hi Guy,
I wonder if you can share your wisdom on this.
I can not find information on how the change of a final drive changes the RR figures (if at all). I researched this topic on google but can't really find any good source of information.
Can you take time out to give me your opinion.
thank you
sean
Posted: May 26th, 2007, 5:52 pm
by Guy Croft
Sean, hi
I'm not surprised you can't find a straight answer to that interesting question! I'll be honest and say I have never thought about it.
Any RR expert care to give an informed answer? I guess I could figure it out if I had not spent all Bank Holiday Saturday day doing flowbench dev.
GC
Posted: May 27th, 2007, 12:03 am
by ohv
Hi,
From my experience there is no change in dyno results caused by wheel size, gear ratio or final ratio, if dyno run is made on gear that provide enough load and enough logged data points.
E.g two dyno runs on different wheels (winter and summer, different sizes) gives usually identical results. Also dyno runs, made on 4th and 5th gear, gives the same figures (on naturally aspirated cars). On turbo cars the situation is different because of different load, which cause faster or slower boost rise (of course this apply only to inertia dyno)
Everything I wrote above apply to 'engine power' measurements. When measuring only 'power on wheels' there will be difference, caused by different rolling friction losses, which are dependent on vehicle speed, which is different on different gear/final drive ratio.
ohv