You don't always need to use a 1:1 ratio, that is usually to minimise losses in the gearbox, but the diff is always there at its own ratio, and the higher the road speed, the more losses you have through the tyres.
Quite a few dynos stick to 3rd or 4th gear to keep road speeds down, and to avoid the roller drums shaking themselves to pieces.
Top road speed in 5th gear on an M3 is about 170mph, and can exceed the rated tyre speed
Ok thanks for that.one question which is the best gear for autos?.my e36 328i was done in topgear,rollers showed speed of 152mph.lewy-t was done at 165mph does it make any difference?
Top gear isn't ideal, at most auto have an overdrive 5th gear, and 1:1 in 4th.
Either way, the torque at the wheels may change, but the power at the wheels should be similar.
If you were in 5th in your 2.8 autobox, it would have revved on to maybe 180+mph
Yes Gazdan happy with my results and that there accurate (as they can be) like you say will all got similar results to prove it was working right.
Just the other graphs on here got me thinking
different dynos give out different bhp figures.
isnt the rule you deduct 15% if your car is FWD from FWBHP to WHP 20% if its RWD and 25% if its 4x4?
Yea, I was wondering the same in regards with the huge tranny losses in some of the graphs. Anyway, FW figures are always the last ones I'm looking at, it's the WHP which counts.
Although, those can be altered too, if the dyno operator wants to, via temp sensors.
Take this one here for ex: 130whp and 200bhp. 70bhp loss through the transmission.. really..
Xmak 330d (24-07-2011)
Was looking into this all a bit more the other day when the froum was down.
Good I sound sad!
As The End has said the result can be so easily affected by the type of dyno. More specifically one using 2 small rollers that pinch the Tyres slightly and ones using one large roller like the one I went on. Further difference can then occur from the width of Tyres on the car and the pressures they run at.
With my car only having 225 width rears and they where pumped up well the losses of energy through them on the single roller dyno would be very small, hence why mine came back with such a small power loss.
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