Hope I don't start any arguments but I'm looking for a general viewpoint and experience of the different people who use rolling roads or know science.
The 2.1 made 206bhp at the wheels...and Saxon said thus 218bhp at the flywheel.
Thats a 6% transmission loss. Is that even possible to have that low of a loss?? I hear a lot about anything up to a 15% loss?
Input/discuss!
Won't be 6% , just re do the flywheel power based on 10-15% losses and will be more accurate... Would be interesting to take it to another dyno and compare also as they tend to vary akot !
Just looked at my dyno sheet, my car was 150 at the fly and 120 at the wheels so that's about 20% lose
Mine pulled 182.1ATF and 165ATW unsure what percentage loss that is?
(25-10-2014, 07:13 AM)Matt-Rallye Wrote: [ -> ]Mine pulled 182.1ATF and 165ATW unsure what percentage loss that is?
About 12%...
Which is what I would expect tbh
9% transmission loss on yours matt
(25-10-2014, 07:19 AM)306Dan Wrote: [ -> ]9% transmission loss on yours matt
I calculated it from both figures and got about 12%?!
How did i do that...
Ive just done a different calculation and 165 at the wheels is 90.6% of the ATF figure...random...so yeah, about 9%!?
The way i look at it, no dyno is accurate. but it gives an even spread between the cars there on the day
so whatever mine is piggy yours is at least 40bhp more
Hmmm.
I like to look at the torque more anyway to be honest
Ugh people seem to get confused with accurate vs correct...
The dyno is highly accurate... The problem lies with the correction of HP atf and atw... If our stupid country wasn't obsessed with flywheel figures, we would be fine!!!
The figure at the wheels is pretty much comparable with every other dyno, end of the day it's measuring torque which is simply the force applied at a foot away... Hardly a complicated calculation... Why don't we all just compare our at the wheels figures... That we we'd actually know what sort of power each persons car is making...
Depends how they've done the coastdown losses tbh, they can be buggered up fairly easy if the ramp down is much faster (i.e, they don't let it slow the same amount of time for lower revving cars as the high ones, etc)
(25-10-2014, 08:18 AM)Ruan Wrote: [ -> ]Why don't we all just compare our at the wheels figures... That we we'd actually know what sort of power each persons car is making...
Because most people see a higher figure and think oh that sounds better and because of that, everyone follows.
End of the day, it just doesn't matter. Its all well and good having shit loads of power but if the delivery of that power is awful, chances are your not going to be as quick as you hope!
Trying to calculate coastdown losses is like trying to calculate power by licking your finger and putting it in the fuel tank...
You're measuring the static losses, not dynamic losses... Surely the power lost when coasting down isn't the power lost when stuffing 320lb.ft through it.
What Ruan said ^^
No transmission creates the same "losses" while coasting down on a rolling road, than when its under full load..
ATW is a far more useful number anyway, given this is the number your acaully putting down on the tarmac, why do you think all Americans use this figure, the UK is just obsessed with ATF figures because there always higher, and depedant on what tranny losses are inputted / generated (99% of dynos dont generate it, they just use an average for the car) its so easy to make the ATF figures wildy higher / lower than they really are...
So my rallye came with 167ATF and now makes that at the wheels with no power mods...
yay
If your wheels were full of cement your transmission losses would be less
When we did the RR at college the losses were roughly 15-20bhp (not sure what percentage that is though, cars were saxo's/106s/Clios and my standard Golf so nothing high powered).
Funniest thing was my mates original Mini though...made 40bhp ATF, lost 20bhp through the tranny!
(25-10-2014, 08:31 AM)Ruan Wrote: [ -> ]Trying to calculate coastdown losses is like trying to calculate power by licking your finger and putting it in the fuel tank....
That works! If it comes out tasting like petrol, that's +50bhp right there!
If it comes out tasting like chips, that's -50.
The problem with ATW figures is they're not actually correct as soon as you put the car on the road, a roller causes far more tyre distortion and heat build up than normal road use. Hub figures/dynos tend to be a lot more consistant there, as it takes that out of the loop, but obviously still don't actually give you a power output that's accurate in the real world.
From what I've seen it tends to be 15-20% on a BE3 box on a dyno dynamics rr
only one thing for it
RAAAACCCCCEE!!!!!
(25-10-2014, 09:36 PM)welshpug Wrote: [ -> ]only one thing for it
RAAAACCCCCEE!!!!!
This!
See you on the track next year matt...in my rear view mirror
(27-10-2014, 08:03 AM)Piggy Wrote: [ -> ]See you on the track next year matt...in my rear view mirror
When your spinning backwards on the grass and im speeding away maybe bacon boy
(25-10-2014, 09:15 PM)Dum-Dum Wrote: [ -> ]From what I've seen it tends to be 15-20% on a BE3 box on a dyno dynamics rr
Lol! Dyno Dynamics Shootout mode simply applies 15% transmission losses on FWD cars because they're aware of how bloody inaccurate it is!
Can't we just agree to only use chassis dynamometers? The fact that you can adjust your hp by pumping your tires harder just makes for inaccurate figures..
Just compare whp figures, its the most accurate thing to compare to. And yes it although it may not be "real hp" to the wheels due to tyre resistance and other things, its still the most comparable thing dyno to dyno. flywheel HP depends on so many factors / is so easy to screw.
How do manufacturers accurately test new cars power? As they all give fly figures obviously. Or do they just estimate with some maths/magic somehow?
Engine dyno!
Stick the engine straight on the power absorbing mechanism... No losses!
Ah, that's a lot more simple than I was assuming!
