[quote author=davelegacy link=topic=9713.msg115660#msg115660 date=1222122431]
[quote author=Cill link=topic=9713.msg115425#msg115425 date=1222090036]
If you're on the rollers or dyno, you can get an exact reading
Dyno is the best method as it is far more acurate
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Actuallly not true and a lot of it depends on dyno make and also on dyno operator.......
dyno's are not gospel by a very long shot..............
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Have a gander around youtube Dave, there is a video out there showing an m3 on a dyno with low pressure tyres and then high pressure tyres, makes 30hp in the difference
Dyno is pure physics, the measuring device is connected straight to the hubs instead of having the vairable caused by wheels and tyres... there is no argument here, physics is physics! Tyres have slip and wheels can be unbalanced and cause a variable, with the dyno, these things don;t matter and I can see no reason the operator of the dyno would have any effect, again, physics is physics. The operator on rollers however can have a big effect and the jerking of the car on the rollers is also causing a measurement difference, again, not so on the dyno
Sorry for the rant, I just believe in the dyno, mechanical power connect directly to the measuring devise...
For the second point and I am very open to correction, I believe that companies choose rollers over dyno's for their cost... I have talked to TDP about his dyno before and the cost of it was massive ( and his skyline wouldn't be able to be mapped in rollers as it would just spin the variable tyres, I'm sure everyone has seen people sitting on the boots of cars to keep them down on a rollers run... looks very professional in my opinion
)... I can;t see the rollers coming anywhere near that cost. I would also be a believer in "you get what you pay for"
Anywho, with the dyno, you can get an acurate engine power reading and the dyno calculates exactly how much power is being lost through the drive train and has no variables like tyres and wheels