Flywheel to Rwkw conversion??

BA2003 · 01-10-2010, 07:29 PM

G'day,

Can anyone tell me how to convert Flywheel kilowatt to Rear Wheel Kilowatt and vise versa?

Cheers

TheInterceptor · 01-10-2010, 07:48 PM

Im not to sure, but i dont think there is a specific calculator as the power losses depend on the cars mechanics? different resisting forces/friction and the likes.

GTP 044 · 01-10-2010, 08:31 PM

I have been told that a rough guide is to divide the flywheel KW's by 1.3 to give you the approximate rear wheel KW's. Not sure how true this is.

Road_Warrior · 01-10-2010, 08:33 PM

I've always used the rough guide of a 30% power loss from FWKW to RWKW

**ebxr8240** · 01-10-2010, 09:14 PM

Multiply or divide by 1.34 to convert kw to h.p or vise versa...
USUALLY and roughly ... rwhp is Fwkw...
Too many variables in transmission to accurately have a formula ...

XBROO · 01-10-2010, 10:14 PM

Quote:

Originally Posted by Road_Warrior

I've always used the rough guide of a 30% power loss from FWKW to RWKW

Yeah that's the old school way but it is only a rough guide.

blackjack74 · 02-10-2010, 10:47 AM

25-30% loss is about right. Which is close to the same difference between KW & HP. So 200 KW at flywheel is about 200 HP at the wheels?

flappist · 02-10-2010, 11:02 AM

Depends on the actual vehicle but a rough guide used by many.

Start with the FWKW of the next model engine above yours (does not have to be the same model or even make)

Multiply x 1.5

Add 5 for every "performance" sticker and 10 for every decibel of noise above the speaker at maccas drive through (exhaust holes and subwoofer are both used)

Add 20 for each bow-tie and shopping trolly wing.

Add 5 for every mm below the legal minimum ground clearance.

Add 1 for each supacheap receipt and 3 for every month interest free you got when you bought your "all rounder" tyre/mag package (n.b. add bonus 50 if you had to use spacers or redrill to fit)

Round the final number up to 10% more than any other car you know (or have seen in a magazine)

388cube_edxr8 · 02-10-2010, 11:03 AM

200 KW is 274 HP. That would mean that the transmission is draining 74 HP from the engine. That is way too much.

The best thing to do would be to find out what sort of gearbox you have, because the power loss is not really a percentage of the total power, but rather a set value for each different gearbox.

You will lose more through an auto than a manual too.

RAPID_BA · 02-10-2010, 11:06 AM

Too many variables, wheel size, weight of flywheel, diff gears, transmission.

For instance ba xt i6 seem to pop out 145rwkw with a claimed 182fwkw but go back a few years and the old 185kw hsv clubbies and 185kw windsors were belting out 120-125rwkw?

3vXT · 02-10-2010, 02:42 PM

When I first dynoed my BA it was loosing 21 or 22% assuming it had 182kw at the flywheel to begin with. Its got a T5 and a 3.45 LSD.

blackjack74 · 02-10-2010, 02:52 PM

Quote:

Originally Posted by 388cube_edxr8

200 KW is 274 HP. That would mean that the transmission is draining 74 HP from the engine.

? 200 x 1.34 = 268. 268 x 0.75 (a 25 % loss) = 201 sounds about right to me. It's trans & diff as well. I'm not trying to be argumentative but that formula has always been close for me for sub 200kw engines. Yes there are many variables but it's close.

BFZF8 · 02-10-2010, 04:32 PM

Quote:

Originally Posted by flappist

Depends on the actual vehicle but a rough guide used by many.

Start with the FWKW of the next model engine above yours (does not have to be the same model or even make)

Multiply x 1.5

Add 5 for every "performance" sticker and 10 for every decibel of noise above the speaker at maccas drive through (exhaust holes and subwoofer are both used)

Add 20 for each bow-tie and shopping trolly wing.

Add 5 for every mm below the legal minimum ground clearance.

Add 1 for each supacheap receipt and 3 for every month interest free you got when you bought your "all rounder" tyre/mag package (n.b. add bonus 50 if you had to use spacers or redrill to fit)

Round the final number up to 10% more than any other car you know (or have seen in a magazine)

That's definitely a tried and true method.

Qwik6 · 02-10-2010, 04:48 PM

Quote:

Originally Posted by GTP 044

I have been told that a rough guide is to divide the flywheel KW's by 1.3 to give you the approximate rear wheel KW's. Not sure how true this is.

I just done this with mine. Found it to be roughly correct.

As people are saying, autos sap more power than manuals, also bigger stalls & lower diff gears take a bit too.

**Revolver** · 02-10-2010, 05:40 PM

Yes as far as I know, manuals are less of a drain on power, autos heavier. Also whatever else is draining power, power steering, alternator, A/C, supercharger (yes they do suck some power, only to give you more). & Any other belt driven accessories.

I asked this question in the driveline-transmission section.... See if I can find the thread for you... I asked what the percentage "driveline loss" was got a few answers. That might help you out.

EDIT: Found it! Only one post, but it backs up the 30% notion...http://www.fordforums.com.au/showthread.php?t=11292240

Flappist.... That was awesome. I didn't stop laughing for about 5 mins, then once I stopped, I heard an Integra with a "cannon" on it. FFAAAAAAAAAAAARRRRRTTTTTT!!!..... Then started laughing again....

388cube_edxr8 · 02-10-2010, 09:30 PM

Not just belt driven accessories drain power, electrical stuff puts more load on the alternator which in turn drains power. That's why electric water pumps provide negligible power gains. In car PC's, fooly hektik stereos, etc. all have the same effect.

KPOJ · 02-10-2010, 09:34 PM

With the race car we are only losing around 10% through the drive train...

The G6ET Spot · 02-10-2010, 11:36 PM

As has been said there are too many variables to have a definite answer.

Like my G6ET dynoed at 242 RWKW stock, they are supposed to be 270 FWKW. So does it mean that I have only lost 10% through the drivetrain or that Ford are understating the power these cars are putting out.

That is just 2 options, maybe the operator didn't strap the car down properly and that gave a higher figure.

See where this is going???

388cube_edxr8 · 03-10-2010, 10:43 AM

How long is a piece of string?

scoupedy · 03-10-2010, 12:37 PM

Firstly accessories don't drain the RWKw as they are already draining the FWKw... everything uses energy the gearbox, driveshaft, gear to pinion interface, axles etc. the more horsepower the less % you use as the box, shaft, diff & axles don't change eg. your 351 with fmx and 9" goes from 220 FWKw too 300 FWKW if you use the same running gear then the drive train power usage for a given rpm will stay the same i.e say 30Kw then you have gone from 190RWKw to 270 RWKw and ~14% loss too a ~10% loss
Every set up is different put a bigger diff in = more loses, Autos use more, larger heavier axles and driveshaft use more as do bigger heavier rims and tyres.
In Engineering we learnt that the best a gear interace can transmit is about 96% (feel free to correct me but it is around this mark) so with two interfaces the best is around ~92%.
10-30% seams resonable

KPOJ · 03-10-2010, 02:33 PM

Quote:

Originally Posted by The G6ET Spot

As has been said there are too many variables to have a definite answer.

Like my G6ET dynoed at 242 RWKW stock, they are supposed to be 270 FWKW. So does it mean that I have only lost 10% through the drivetrain or that Ford are understating the power these cars are putting out.

That is just 2 options, maybe the operator didn't strap the car down properly and that gave a higher figure.

See where this is going???

Or is your dyno man giving 'customer happy' figures, this is the case in most situations, seen dyno's up to 18% out.

**Revolver** · 03-10-2010, 05:05 PM

Quote:

Originally Posted by scoupedy

Firstly accessories don't drain the RWKw as they are already draining the FWKw... everything uses energy the gearbox, driveshaft, gear to pinion interface, axles etc.

You just contradicted yourself. If your draining FWKw, your in turn Draining RWKw, Hence when you add/remove a belt driven accessory, it decreases/increases the FWKw & RWKw at the same time Respectively. Not just FWKw. Your cant add or lose HP from one OR the other. It MUST be both. It just means the power you just gained also loses the same percentage of power through the driveline....

Aulpgute · 03-10-2010, 05:49 PM

Slightly off topic but semi relevant, bout 15yrs back my factory XD 351/FMX ute with exhaust and small cam produced 195rwhp thru a BW 3.23 diff and days later after a 3.25 9 inch diff conversion produced 188rwhp under the same conditions. Worth a mention highlighting the parasitic losses of runing a much heavier diff than the original.

Aulpgute · 03-10-2010, 05:54 PM

Slightly off topic but semi relevant, bout 15yrs back my factory XD 351/FMX ute with exhaust and small cam produced 195rwhp thru a BW 3.23 diff and days later after a 3.25 9 inch diff conversion produced 188rwhp under the same conditions. Worth a mention highlighting the parasitic losses of turning a much heavier diff than the original.