rwkw to fwkw?

[Aaronsbt1]

hi guys how do you convert rwkw to fwkw? 151.1kw at the wheels would make it ??kw at the flywheel.

[Philthy]

+ about 30% for an auto. A bit less for a manual (25% or so I think)

[Dr.304]

lol when i read the topic heading i took it like this = rear wheel KW to front wheel KW.

LOL

[Rolla_Rolla']

lol when i read the topic heading i took it like this = rear wheel KW to front wheel KW.

LOL

Exactly what i thought lol,

Anyone have the exact formula ?

[immortality]

there is NO exact formula. power at the wheels is effected by so many different things that there is no way to calculate flywheel HP from rear wheel HP. just changing the diff oil can effect power output measured at the wheels. drivetrain mass, transmission type, friction/oil type all effect output.

[danja]

As has been said, the only way to get a precise figure is to put the engine on an engine dyno, but a good rule of thumb is usually fwkw = rwhp.

If you have 151Kw at the wheels, that's 202rwhp, so you could estimate about 200Kw at the engine.

[Aaronsbt1]

ok thanks guyz, was just wondering coz im really bored lol

[Blown V6 Hatch]

Yeh, as Danja said, Rwhp roughly translates to Fwkw. It's not dead accurate, but it'll be close enough.

[TrikkBen]

Worked at a dyno tuners, with both Chassis and Engine dynos. The rule of thumb is, + a Third of your RwKw.

[Sphinx]

i'd say that's about right..

[crozier84]

Agree. so far all my cars have lost about a third of rwkw's when you add up the extra kw's from mods onto the original engine kw's

[peckzz]

but then you gotta think bout it, u got a shit laggy gearbox, its gonna lose more power compared to a fresh one ay? so there is no exact method as everycar will be evan .1 of a kw different, well thats my opinion any way

[wikky]

but then you gotta think bout it, u got a shit laggy gearbox, its gonna lose more power compared to a fresh one ay? so there is no exact method as everycar will be evan .1 of a kw different, well thats my opinion any way

As stated in post #5 by Immortality.

[peckzz]

oh bloody hell didnt see that 1 lol sorry

[VN Wagz]

Umm lets clear a few things up.

In a most STOCK setups for medium/low powered cars, the 25- 30% ruling as fairly accurate, depending on all the variables that people have listed above. However, all this changes once your power figures go up....

Example: Generic V8 commodore... manual or auto, whatever.... 165kW flywheel, makes 125rwkW (its an example, dont question it!)

Loss is 40rwkW (24%), the car makes 166rwhp/125rwkW.... now, do something to improve its power output- stroker, blown, or similar.

So, lets say that the stock drivetrain can cope with 500rwhp without slipping (good box, clutch, diff etc). Car is now making 500 rwhp, which is 373rwkW.

A lot of people (even those i know, hardcore petrol heads included!) will tell me that their (example again!) 500rwhp car is making 500kW at the engine. However, 500kW is 680hp i say to them. So, your car is losing 180hp somewhere?? Ahhh, no its not.... you just like big numbers :P

Assuming your auto/manual/clutch/driveline etc isnt slipping and mashing itself, and you havent radically altered the wheel/tyre combos you shouldnt be losing anymore than the 40kW that was initially lost in the first place. Even if you put a bigger clutch setup in place, or rebuild your auto you wont be losing much more than a couple of kW/hp over a stock setup for efficiency, in most cases its better!

So, 373 + 40kW= 413kW @ engine. Yes, its 565hp, but its nowhere near the 680hp that some would claim....

The higher your power goes, the lower your driveline loss % becomes overall.... For the example above, the drivetrain loss is now

STOCK 40kW/165kW = 24% loss
MODIFIED 40kW/413kW = 9.6% loss

keep going with the power upgrades and the % keeps falling...

this kind of strange thinking has been around for years, i even heard several competitors at Summernats on the dyno (with hardcore cars) saying the same things- oh, i can make 800 rwhp, which is 800kW at the engine (1200hp+). Funnily enough, a lot of these cars (at the track) seem to run times and Mph like a lot of the other 850-900 FLYWHEEL hp cars...

Furthermore, i read an article online a while back where some guy had a "600kW" RB30 built for his VL turbo, and was expecting it to make around 600rwhp. Not surprisingly it made 725rwhp, even through a hi-stalled powerglide and 9" diff! That 800hp @ flywheel engine was losing 75hp (50kW) putting it to the wheels (built roller internals glide, alloy centre 9" diff etc), the guy even got onto the shop that built it saying they must have wound it up way past 600kW to get that!! They spent a while telling him how it works, explaining what the go was.

Confused? or enlightened?

Pls let me know if anything here needs clarifying

**VN Wagz**

[TrikkBen]

You have way to much time dude...

[VN Wagz]

^^^^^^^^^ But, im right arent i? LOL

I told this exact thing to a guy at a cruise the other day, who was telling everyone his car makes 350kW.... cos his dyno sheet said 350rwhp....

when confronted with my brutally straightforward logic (in front of his mates, who thought he was full of it as well) his reply was to pause and then say "nahhhhhhh, i think you're wrong!

[QldKev]

^^^^^^^^^ But, im right arent i? LOL

I told this exact thing to a guy at a cruise the other day, who was telling everyone his car makes 350kW.... cos his dyno sheet said 350rwhp....

when confronted with my brutally straightforward logic (in front of his mates, who thought he was full of it as well) his reply was to pause and then say "nahhhhhhh, i think you're wrong!

My understanding was that the loss was not a flat line. ie in your example 40rwkW was the loss of the engine @ 165kW flywheel, makes 125rwkW
But if you increase your torque you will also increase the resistance as you are suddenly applying more rotational energy. This is not lineal as most people think, if you double your torque will not necessay double the losses, but rwkw losses will change.

QldKev

[VN Wagz]

My understanding was that the loss was not a flat line. ie in your example 40rwkW was the loss of the engine @ 165kW flywheel, makes 125rwkW
But if you increase your torque you will also increase the resistance as you are suddenly applying more rotational energy. This is not lineal as most people think, if you double your torque will not necessay double the losses, but rwkw losses will change.

QldKev

Oh, i understand that with rises in torque and horsepower that more losses will expand beyond the initial amount that a lower power setup would make due to more rotational force through box and diff, but its never going to jump wildly to accomodate the huge losses that people crap on about.. you'd see a few % increase over the loss of a stocker, assuming the clutch/auto internals dont slip/blow up etc... my examples are ones where we'd assume the stock engine is running a roller-internals powerglide and mega-dollar diff setup which would lose bugger all no matter what was put in front of it- low or high power

I've heard of people with sub-standard autos and/or convertors swapping them for properly built units and magically finding a stack more kW at the wheels.

[QldKev]

Agree with you there. Be good if a place with an engine and chassis dyno actually did some stats.
I.e. Get a stock engine setup and chassis dyno it,
Then rip the engine out do an engine dyno,
Do the rebuild/blower/etc
Re dyno the engine
Then put it back in the car and get another rwkw reading.

Talking about losses in the gearbox etc, when I used to live in Perth my mate would even drop his gearbox oil and put in thin shit for the drags, and then put the heavier stuff back in when he finished. Not sure what the difference in kw he actually got doing it, but he claimed it did knock of a bit of time.

[VN Wagz]

well, street commodores did an article with their "STREET" monaro project years back- replaced the engine, gearbox and diff oil with Royal Purple stuff and got a repeatable 4kW gain, so there is lots to be said for different viscositys/shear strengths having different results...

dropping the oil in an auto and changing to other stuff for the drags- sounds scary. Seeing how there is so much relying on oil in an auto, i wouldnt be game....

I've heard of people doing the same with diffs as well. Thinner oil in the diff- would be worth it tho? compared to the engine and auto (lots of oil) there aint that many rotating parts in a differential, i wouldnt think the gains would be as great.

[QldKev]

For 4kw sounds like it is not worth it; better of spending the money on other mods.

Back in Perth my mate had a manual gearbox for the oil, but still at 4kw overall maybe the gearbox gave him a whole 1kw lol

QldKev

[AqaumarineVR]

Roughly,give or take,your RwHp eqauls FwKw
EG-345RwHp = 345FwKw

[wikky]

Roughly,give or take,your RwHp eqauls FwKw
EG-345RwHp = 345FwKw

As post #6 & 8 stated.......