Driveline Power Losses - What percentage ??

[Rodge]

So last Friday my stock SC GT-P fitted with a new air filter only, spun up 312.9 rwkw's on CTB Performance's Mainline dyno which many in the know on here seem to have a lot of respect for that brand of dyno and think its very accurate and I'm pondering what that means in terms of crankshaft power ?

For quite a while now I've had the opinion that there's about 16-17% driveline losses which would tend to indicate about 375KW's at the crank, (312.9/0.835) or 500 horsepower in the old money (375 x 1.34) so I'm more than content with that.

But are the driveline losses actually higher ???
Here's a clip of the 375KW HSV W427 making 295 rwkw's on a dyno, not sure what brand but that's 21.4% driveline losses for a manual rear wheel drive car making similar horsepower and mine's a ZF auto which are usually less efficient at power transmission than a manual. http://www.youtube.com/watch?v=b4YeHu5Qw3o

Intertesting article on the subject for anyone wanting to drill down into this subject a bit http://www.modified.com/tech/modp-10...s/viewall.html

I've read that Dyno's that affix onto the hub of the rear wheel generally give around 6% higher rwkw ratings than roller type dyno's so it seems that there's 6% driveline loss just through the inertia effect of the tyres and possible inefficient tractive effect from the tyres on rolling dyno's. I would have thought there's more than 10% driveline losses through the rest of the driveline, gearbox, drive-shaft, diff and half shafts ? If we assummed the W427 dyno result is representative and that the crankshaft output is really 375 kw's and applied the same 21.4% driveline losses to my car we'd get 398 Kw's at the crank (312.9/.786). Anyway it appears my car is making somewhere between 375 and 400 Kw's not too shabby at all for a stock SC GT-P

Got any thoughts on driveline loss percentages ?

[prydey]

here's another can of worms...

are the losses a percentage? or are they a set value?

example,

you establish that on a stock vehicle, there is 20% loss in the driveline, giving you a rear wheel kw rating 60kw less than the flywheel. if you then increase the flywheel power by 50kw, are the losses the same? or do they also increase? i have read a few articles which suggest that the losses remain very similar, regardless of increases at the flywheel.


i personally don't believe there is any set figure and it will vary every time, even on the same car. way too many variables. at the end of the day, it means very little and is mainly for school and pub chat.

[Rodge]

Higher horsepower generates more heat and friction a subject that was alluded too to some extent in the article I referenced.

[XR Martin]

Running a car down the 1/4mile and putting the trap speed and weight into a specific calculator is more often than not a more accurate method of calculating engine power.

[Silver Ghia]

Originally Posted by XR6 Martin

Running a car down the 1/4mile and putting the trap speed and weight into a specific calculator is more often than not a more accurate method of calculating engine power.

I would have thought more variables (ie. drag, weight, wind, ground slope) come into the equation when you do that, plus you would still have the mechanical losses in the driveline and tyres.

I agree that the mechanical efficiency in the driveline and tyres would vary dependent on engine rpm, gearing and speed of the particular vehicle. I always thought 20 - 25% was the usual loss between the flywheel and the ground.

[ebxr8240]

Its also the way dyno's read power levels..
Yes heat and friction builds up with power but not at the same % rating..

[mik]

i`ve always wondered what the difference in driveline drag is on lets say an XY GT to an FG GT, the XY runs through 4 slotter and a heavy nine inch diff with big axles, on the other hand, the fg runs a gearbox with 2 extra cogs, a 2 piece tail shaft? an irs diff with 2 half shafts universals at both ends an extra wheel bearing in the knuckle, as rodge mentioned tyre/rubber friction, some horse power used to deform the rubber slightly as it rolls, even the difference between a car with some miles on it with slightly looser tolerances and having to push less lubricant around through bearings would have some bearing(scuse the pun ) on losses, not to mention friction modifiers in lubricant`s etc,, my guess is power losses would be slightly different on every single car.

[Psi-Pop]

Originally Posted by mik

i`ve always wondered what the difference in driveline drag is on lets say an XY GT to an FG GT, the XY runs through 4 slotter and a heavy nine inch diff with big axles, on the other hand, the fg runs a gearbox with 2 extra cogs, a 2 piece tail shaft? an irs diff with 2 half shafts universals at both ends an extra wheel bearing in the knuckle, as rodge mentioned tyre/rubber friction, some horse power used to deform the rubber slightly as it rolls, even the difference between a car with some miles on it with slightly looser tolerances and having to push less lubricant around through bearings would have some bearing(scuse the pun ) on losses, not to mention friction modifiers in lubricant`s etc,, my guess is power losses would be slightly different on every single car.

Every time you have a mechanical coupling your going to be losing some power thru it so in that regard you would imagine the FG to have more than a XY.

I just don't think its measurable, there is too many factors that come into play on a chassis dyno. I know my car when we tuned the base tune in came in at 297rwkw(403hp), that's thru a C4 and a big convertor yet it ran 10.9x's @ 121-125mph thru the traps in a 3550lb car. That indicates at best of 536hp at motor. So that's a loss of 133hp.

Its far easier to work out engine HP from 1/4mile performance and weight. Horsepower after all is how much weight can be shifted in a time.

[Rodge]

some horse power used to deform the rubber slightly as it rolls

Good point and I liked all of your post. The new Eco tyres used by some manufacturers have super stiff sidewalls to reduce these losses.

Another loss point is traction on the dyno depending on how good your tyres are. I have heard of guys getting slightly better numbers on a dyno just with a fresh set of tyres which I guess illustrates the point.

Been digging on the Net, AWD loses the most, next is RWD then FWD.
Auto's lose more especially older less efficient ones.

My long held belief of 16-17% seems a bit light from what I've been reading.
Seems to be a general consensus on the LS1 forum that the circa 21% loss of the W427 is pretty much representative of what other HSV and Holdens have experienced for manual boxes, slightly higher for auto's. Other avenues looked into are talking around about the 20% mark as a general rule of thumb for rear wheel drive cars which I'm starting to think seems like a more realistic yardstick to use, especially for an auto.

[zilo]

25-30% for a RWD
15-20% for a FWD
30-35% for an AWD


That's what I reckon.

Ignoring happy dynos, heat soak, tyres, worn transmisssions etc etc etc

[FPV GTHO]

I usually guess at about 25% for modern 4spd auto Falcons.

[FPVF6X201]

My stock AWD F6X 270 showed 205awkw (24% loss). So if you guys with RWD only lose approx 20% thats 4% extra lost driving two extra wheels.

[FPV GTHO]

Originally Posted by FPVF6X201

My stock AWD F6X 270 showed 205awkw (24% loss). So if you guys with RWD only lose approx 20% thats 4% extra lost driving two extra wheels.

Ahh but that's assuming it was really 270kw at the engine. The first BA2 Typhoons were pulling 200rwkw as well, but once they went back on sale after the clutch drama they magically jumped to 220rwkw.

[FPVF6X201]

Originally Posted by FPV GTHO

Ahh but that's assuming it was really 270kw at the engine. The first BA2 Typhoons were pulling 200rwkw as well, but once they went back on sale after the clutch drama they magically jumped to 220rwkw.

So are you saying my 270 is more than 270 or less? And yes for those playing at home, its the same motor as the Typhoon/Force6.

[Rodge]

Originally Posted by FPVF6X201

So are you saying my 270 is more than 270 or less? And yes for those playing at home, its the same motor as the Typhoon/Force6.

I had a BF2 Typhoon for 3 years and there is no way in this wide world it was only making 270 Kw's at the crank, popular conjecture on here is they're circa 290-295 kw's at the crank. If we said it was 290 and you got 205 that's 29% losses for a 4WD which is spot on the sort of figures I was reading about earlier today on other site's which indicated circa 28% as a good rule of thumb for AWD sports vehicles.

Pretty sure most of the stock 270 motors in Typhoons are getting in the 220-230 rwkw range so without in any way taking anything away from the F6X which are a brilliant and extremly versatile vehicle, in my opinion an AWD is about 8-10% less efficient at power transmission on the tarmac.

[Aulpgute]

Just looked up some figures from way back (1990) on my XD factory S Pack 351 ute. Had a mild engine with Comp Cams 260 cam, cleaned up 2v heads with 4v valves, flat top pistons, HM Headers with twin 2 1/4 system with balance pipe, graphed up dizzy and well set up Rochester Quadrajet (against the grain I know but worked better than any other street carb I tried at the time). Running through the stock FMX auto and 4 pinion Borg Warner diff it had 219 hp at the wheels. Point I'm getting to is that 3 weeks later on the same dyno under the same conditions after fitting a 9 inch disc rear end the power dropped to 207hp. The BW was a 2.92 ratio and the 9 inch was a 3.0 so if anything the difference in ratio favoured the 9 inch. So basically 12 hp was lost turning the 'industrial strength' diff as opposed to the car spec BW. PS Damn I still wish I had that ute....

[FPVF6X201]

Originally Posted by Rodge

an AWD is about 8-10% less efficient at power transmission on the tarmac.

Probably true. But it does allow me the traction on takeoff that RWD's dont have (in stock form anyway).

Kinda glad to know i "may" have a lot more than 270kw though lol.