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InExtremis Enthusiast

InExtremis

Posted
Posted

This is a question that is very vague to answer, and it also a question that doesnt really matter. According to some stuff that ive read, the power at the wheels is 80 - 85% what it is at the engine. Still this is just an estimate, and like I said, who really cares ...

Oh, in case you dont know the kw - bhp conversion .. its x 1.341 ... so if you have 245 kW at the wheels, you have about 328 rwhp. Not that that really matters either .. its just a measurement and i rekon ppl often quote it just cause its a bigger number and sounds better ... but not always.

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HSVKLR Community Regular

HSVKLR

Posted
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There is no definitive equation for determining flywheel horsepower from rear-wheel horsepower.

InExtremis you said that you believed it was 80-85%, well i heard it was between 67-75% (2/3 and 3/4), so that proves that it depends on multiple variables. All wheel drives also lose much more power through drivetrain loss. Ill outline a few variables that i know of but someone with dyno experience can elaborate:

* wheel/tyre size

* how well the car puts its power down

* weight distribution

In the latest MOTOR mag they had a Holden v Ford comparison and dynoed all 7 cars. Some interesting results:

* FPV GT = 290Kw@fly but made 225Kw@wheels

* HSV GTS = 300kw but made 222Kw@wheels

* Holden Caprice = 245Kw@fly but made only 158Kw@wheels

* Commodore SS = 235Kw@fly but made 182Kw@wheels

* Commodore SV8 = 235Kw@fly but made 178Kw@wheels

As you can see descrepancies are apparent in these examples. One phenomenon did occur to me the cars that performed best had more weight over the rear axles...

Hope this helps...

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HSVKLR Community Regular

HSVKLR

Posted
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For dyno-testing yes more more weight in the back will give better results (generally speaking) for RWD cars. Thats why sometime you see guys sitting in or on the boot of cars being dynoed!!!!

As for on the road, there is a fine line between good power down and bogging, and more finely adding extra weight to aid power down and the detriment of having a heavier car (the heavier the car the worse power to weight ratio).

Think of a leaf sprung suspension equiped ute with big horsepower. There's 3/5ths of stuff all weight in the back therefore there is going to be a difficulty in putting the power to the ground because the tyres wont be sitting as heavily on the road...

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dAVE Grand Master

dAVE

Posted
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only bad thing with this info is.... you are assuming that they are actually the quoted figure @ fly. Figures could well be totally correct, and what im saying would have no relevance.. but it may not be the case .

Originally posted by HSVKLR

In the latest MOTOR mag they had a Holden v Ford comparison and dynoed all 7 cars. Some interesting results:

* FPV GT = 290Kw@fly but made 225Kw@wheels

* HSV GTS = 300kw     but made 222Kw@wheels

* Holden Caprice = 245Kw@fly but made only 158Kw@wheels

* Commodore SS = 235Kw@fly but made 182Kw@wheels

* Commodore SV8 = 235Kw@fly but made 178Kw@wheels

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rb25 Grand Master

rb25

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Roughly the number of horsepower at the rear wheels is the same number of kW's at the flywheel.

so in butthead's case 245rwkw = 327rwhp

therefore if the car has 327rwhp, the engine produces 327kW (436hp) at the flywheel (roughly)

i dont think this would apply to all cars but seems to be pretty close on rwd skylines.

hope that helps....

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HSVKLR Community Regular

HSVKLR

Posted
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Haha no worries InExtremis - it's interesting that they did an article with dyno results of all our "favourite" australian cars.

Just out of interest the XR6T which won the comparison for best all round ability made 185Kw@wheels... not bad eh?!! They even made mention of the "R32 Skyline" in the article - saying not since then has a 6cyl decimated the opposition in such a way....

Btw RB25 i like your formula in working it out - very interesting but if you apply it a stock R32 GTSt see what happens:

Roughly 110kw@wheels=147.4hp@wheels

therefore 147kw@flywheel (158/162kw stock)

Almost but not quite....

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