KW at fly different to wheels, What about HP?

[SSEEYA]

Just wondering, i know that you've got a certain amount of kw at the fly, and you lose power through parts by the time its at the wheels, but what about horsepower?? does it apply for that too??
or if u have 300 horsies at the fly u've still got it at the wheels...
can some one clear this up ??

[vt350phantom]

hp is just another unit of power. If you lose say 30kw through the drive train then you are losing 30 x 1.34 hp. Just like if you lose 2.6 L of water you lose what ever the hell 2.6L is in gallons

[Trek52]

from what I can gather if you have 300hp at the wheels that would be about 300kw at the flywheel, give or take a bit, I think :)

1kw = 1.34hp

so take my car it has 312.8 rwhp = 233 rwkw = 310fwkw = 415fwhp

I hope that is right !!! I could be wrong though I have some bragging to do at the pub if my car has 400 plus hp !!!

[Gatecrasher]

Dude, flywheel horsepower is measured at the flywheel of the engine on an engine test stand or dyno. This, of course, does not take into account any of the vehicle drivetrain or accessories, such as the fan, alternator, power steering, etc.

Rear-wheel horsepower is measured at the rear wheel of the vehicle on a chassis dyno. This provides a real world picture of how the engine operates as it is installed in the vehicle and used by you.

The difference between flywheel horsepower and rear-wheel horsepower will vary from vehicle to vehicle, depending on many factors but rear-wheel horsepower is usually between 18% - 25% LESS than flywheel horsepower.

So in answer to your question... no, if you have 300 horsies at the fly you don't have that same figure at the wheels.

But as vt350phantom said, "hp" is just another unit of power. Much the same as Centimeters are to Inches --> Horsepower is to Kilowatts.

- Dave

[andrewdisco]

i've never understood how some people apply a flat percentage loss to the drive line ? i.e 30% is what many people use...

I usually estimate it at around 60-70kw regardless of the engines output..

you couldn't say that if an engine was 1000kw that it was losing 300 in the drive line :p

my magna lost almost as much in the driveline as my LS1... and stock it was only half the flywheel kw's...

[GTO_]

i've never understood how some people apply a flat percentage loss to the drive line ? i.e 30% is what many people use...

I usually estimate it at around 60-70kw regardless of the engines output..

you couldn't say that if an engine was 1000kw that it was losing 300 in the drive line :p

my magna lost almost as much in the driveline as my LS1... and stock it was only half the flywheel kw's...

You can't apply a flat 60-70kw, and how do you come to that figure?:confused: Ran test's on different vehicles? Combos? FWD? RWD? AWD? ... It works via % loss not 60-70kw on everything ... Now it's not always going to be 30%. Sometimes it's lower than that, sometimes higher. So many different variable thats why its a % loss the drivetrain takes up not one flat figure like u assume.

Some people do use the 300rwhp = 300fwkw, because when you do the conversion in most cases around the 300-400rwhp mark the flywheel kw figure you get is pretty close believe it or not.

[JimmyXR6T04]

from what I can gather if you have 300hp at the wheels that would be about 300kw at the flywheel, give or take a bit, I think :)

1kw = 1.34hp

so take my car it has 312.8 rwhp = 233 rwkw = 310fwkw = 415fwhp

I hope that is right !!! I could be wrong though I have some bragging to do at the pub if my car has 400 plus hp !!!

As others have stated, its really hard to compute engine/flywheel figures when the initial dyno run measures at the wheels. And its best to keep it the way it was measured. Its all just speculative otherwise. Mine made 304rwkw or 407rwhp... so i could speculate that its got 500hp.. but that might not be correct. Best bet is to just say what it made at the wheels, although not all people will always understand those figures.

At best, you can only do a very rough estimate of the flywheel figure. In the car modding world though, who talks of flywheel figures?? Unless done on an engine dyno.. Usually the people who don't have enough rear wheel power, so they inflate their flywheel figure :hide:

[kart_racer]

I usually estimate it at around 60-70kw regardless of the engines output..


I drive a Hyundai Excel...that kind of driveline loss would leave it with 4kw at the wheels!!!

[Gatecrasher]

In the car modding world though, who talks of flywheel figures?? ...usually the people who don't have enough rear wheel power, so they inflate their flywheel figure...
lol! So true!

[andrewdisco]

I drive a Hyundai Excel...that kind of driveline loss would leave it with 4kw at the wheels!!!

Haha good call i guess...

Although i reckon if you ran a drive line and gearbox the same strenth as a family car and whacked some fat 18" wheels on it there wouldnt be much left getting to the road :p

GTO... nope haven't run tests just speculating. It sounds like you have though ? so I'm happy to be educated

I just don't see why the resistances from tyres and driveline would be proportional rather than flat. But as i said i'm happy to have it explained to me as I'm (obviously) far from being an expert on the matter.

[VU_SS_UTE]

I drive a Hyundai Excel...that kind of driveline loss would leave it with 4kw at the wheels!!!

Thats about right isnt it.... jk :P

[payaya]

Haha good call i guess...

Although i reckon if you ran a drive line and gearbox the same strenth as a family car and whacked some fat 18" wheels on it there wouldnt be much left getting to the road :p

GTO... nope haven't run tests just speculating. It sounds like you have though ? so I'm happy to be educated

I just don't see why the resistances from tyres and driveline would be proportional rather than flat. But as i said i'm happy to have it explained to me as I'm (obviously) far from being an expert on the matter.

Laws of physics i guess!!

Engines have their operating efficientcy, just like every other powered device! Say an engine is 60% efficient increasing power will not increase its efficienty!

[Waabs]

I just don't see why the resistances from tyres and driveline would be proportional rather than flat.

Again I wouldn't really know but in my probably hole ridden logic I can't see how it's a % loss either. If you have two cars with identical drivelines but one engine produces 500fwkw and the other 300fwkw wouldn't the driveline take out the same amount in each car rather than a percentage?

[olddicko]

[QUOTE=andrewdisco;697499]i've never understood how some people apply a flat percentage loss to the drive line ? i.e 30% is what many people use...

....you couldn't say that if an engine was 1000kw that it was losing 300 in the drive line :p

QUOTE]
Agreed. No way can you say that it is a flat 30% or whatever loss accross the board. Drivetrain loss is not directly proportional to flywheel power, it couldnt possibly be.

Fair enough 28 - 30% sounds, and has pretty much been proven, to be a ROUGH guide on our LS1's - remembering that the majority of us are all putting out the same amount of power at the rear bags. Now boost our power up to the kind of power the FI (TT and Supercharged) boys are putting out and its a complete different ball game.

[Dacious]

Bigger motor, bigger gears, bigger universals, bigger crownwheel/pinion, bigger tyres, more drag. A typical north-south driveline with 90 deg. bevel is known to lose a consistent 10-12%. East-west motor with axial gears loses a little less. Add friction loss through trans gears/bearings and diff, driveshaft unis, and you're up to 15-20% in a manual. Add in extra power loss for auto.

Add heat (friction) and force (weight, clamping force to dyno drum). Yeah, you could lose 300hp out of 1000 tranferring power to the ground.

Friction loss is exponential. If you lose 25hp at 2,000rpm, you will likely be losing more like 100hp at 4,000rpm in a low friction design. A Ford Cosworth V8 with DOHC 32 valves as used in Formula 1 cars a long time ago lost 60kw or 80hp through the chain-driven cam gear (triple valve springs) at peak revs. Your motor might develop a consistent 500nm between 2,000rpm and 6,000rpm, but hp (which is force by speed) won't be three times as high at 6K as 3K. What stops hp growth being linear is friction and pumping losses along with gas resistance to flow at higher speeds.

Your fat 10" 250 section sticky tyres are creating plenty of drag themselves, like walking in sloppy mud with gumboots. Why they run 4" wide rockhard tyres at 100psi in world economy attempts. Not much good at putting 300Kw to the ground, but, so we use the wide ones.

[andrewdisco]

There's probably a million calculations were not factoring in...

So if you had a dad and a son push the same size trolly, but the son could push one with 20kg of weights in it and the dad could push one with 100kg of weights in it. Then the trolly's weight and resistances could be deemed to be representive of the same proportional overheads % wise in both cases ?

I just wonder, applying the 30% rule to the new VE then they'd only be making 189rwkw. But instead they seem to be losing about 60 which is about the same as what the 220kw VT II's were losing.

Maybe the losses are partly fixed and partly proportional ?

[dyno junkie]

i've never understood how some people apply a flat percentage loss to the drive line ? i.e 30% is what many people use...

I usually estimate it at around 60-70kw regardless of the engines output..

you couldn't say that if an engine was 1000kw that it was losing 300 in the drive line :p

my magna lost almost as much in the driveline as my LS1... and stock it was only half the flywheel kw's...

If your Magna is an automatic then your probably right.

There has always been a huge difference in RWHP between automatic and manual 3.0 & 3.5 litre Magna's.
Either they run a very different tune or the automatics soak up a lot of power.

[payaya]

There's probably a million calculations were not factoring in...

So if you had a dad and a son push the same size trolly, but the son could push one with 20kg of weights in it and the dad could push one with 100kg of weights in it. Then the trolly's weight and resistances could be deemed to be representive of the same proportional overheads % wise in both cases ?

I just wonder, applying the 30% rule to the new VE then they'd only be making 189rwkw. But instead they seem to be losing about 60 which is about the same as what the 220kw VT II's were losing.

Maybe the losses are partly fixed and partly proportional ?

More efficient drivetrain, underestimating power figures etc.


If your Magna is an automatic then your probably right.

There has always been a huge difference in RWHP between automatic and manual 3.0 & 3.5 litre Magna's.
Either they run a very different tune or the automatics soak up a lot of power.

Maybe Mitsu were dodying the figures.

[wagnman]

Does anyone know of any dyno tests done to test things like different diff/trans/engine oils, bearing greases, tyre pressures, etc etc to see what improved the drive line losses to increase the rwkw figures?

[VYBerlinaV8]

As fun as RWKW vs FWKW is, the only measure that I think counts is the performance - and then only in terms that match the owner's usage. Many here use 1/4 mile time, some use 0 - 60 ft, etc.

Personally I like to look at 0-60, 0-80, 0-100, 0-120, 80-120 and standing quarter, to try to build a picture of the car's performance.

The difficulty is about trying to compare vehicles. Different cars, different days, different dynos ... you get the picture.

[chops]

There has always been a huge difference in RWHP between automatic and manual 3.0 & 3.5 litre Magna's.

Not a huge difference, both were zero unless it was an AWD model. :stick: