Power-to-weight ratio Information & Power-to-weight ratio Links at HealthHaven.com

Power-to-weight ratio (or specific power) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measurement of actual performance of any engine or power sources. It is also used a measure of performance of a vehicle as a whole, with the engine's power output being divided by the curb weight of the car, to give an idea of the vehicle's acceleration.

[edit] Power to weight (specific power)

The power-to-weight ratio (Specific Power) formula for an engine (power plant) is the power generated by the engine divided by weight of the engine as follows:

$\begin{matrix} \mbox{P-to-W}&= P/W \\ \end{matrix}$

A typical turbocharged V-8 diesel engine might have an engine power of 250 horsepower (190 kW) and a weight of 450 kilograms (1,000 lb), giving it a power-to-weight ratio of 0.42 kW/kg (0.25 hp/lb).

Examples of high power-to-weight ratios can often be found in turbines. This is because of their ability to operate at very high speeds. For example, the Space Shuttle's main engines use turbopumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine's combustion chamber. The liquid hydrogen turbopump is slightly larger than an automobile engine (weighing approximately 320 kilograms (700 lb)) and produces nearly 70,000 hp (52.2 MW) for a power-to-weight ratio of 164 kW/kg (100 hp/lb).

The actual useful power of an entire jet engine or rocket engine can be calculated, but varies with speed (power is force times distance over time or simply force times speed). For jet engines there is often a cruise speed and power can be usefully calculated there, for rockets there is typically no cruise speed, so it is less meaningful.

[edit] Examples

[edit] Engines

Engine	Power-to-weight ratio	Total Power Output
Turbocharged V-8 diesel engine	0.25 hp/lb / 410 W/kg^{[citation needed]}	250 hp / 186 kW
Pattakon OPRE two struck diesel	1.4 hp/lb / 2.3 kW/kg^[1]	70 hp / 50 kW
49-PI Type II Wankel engine	1.7 hp/lb / 2.8 kW/kg^[2]	1.252 hp / 0.934 kW
BMW P84/5 2005 (Formula 1)	4.6 hp/lb / 7.5 kW/kg^[3]	925 hp / 690 kW
Boeing 777 GE90-115B Jet Engine	6.10 hp/lb / 10.0 kW/kg^{[citation needed]}	111,526 hp / 83,164 kW
Space Shuttle Engine Turbopump	100 hp/lb / 160 kW/kg^{[citation needed]}	70,000 hp / 52,000 kW

[edit] Vehicles

Power-to-weight ratios for vehicles are usually calculated using curb weight (for cars) or wet weight (for motorcycles) - in other words, excluding weight of the driver and any cargo. This could be slightly misleading, especially with regard to motorcycles, where the driver might weigh 1/3 to 1/2 as much as the vehicle itself.

Vehicle	Power	Weight	Power-to-weight ratio
Benz Patent Motorwagen 954cc 1886 ^[4]	560 W / 0.75 bhp	265 kg / 584 lb	2.1 W/kg / 779 lb/hp
Force Motors Minidor Diesel 499cc Auto rickshaw^[5]^[6]	6.6 kW / 8.8 bhp	700 kg / 1543 lb	9 W/kg / 175 lb/hp
PRR Q2 4-4-6-4 steam locomotive with tender 1944	5956 W / 7987 bhp	475,900 kg / 1,049,100 lb	12.5 W/kg / 131 lb/hp
TGV BR Class 373 high-speed locomotive 1993	12,240 kW / 16,414 bhp	816 t / 1,798,972 lb	15 W/kg / 110 lb/hp
International CXT 2004 ^[7]	164 kW / 220 bhp	6577 kg / 14500 lb	25 W/kg / 66 lb/hp
Ford Model T 2.9L 1908	15 kW / 20 bhp	540 kg / 1200 lb	28 W/kg / 60 lb/hp
Messerschmitt KR200 Kabinenroller 191cc 1955	6 kW / 8.2 bhp	230 kg / 506 lb	30 W/kg / 50 lb/hp
Tata Nano 624 cc 2008	26 kW / 35 bhp	635 kg / 1400 lb	41 W/kg / 40 lb/hp
Suzuki MightyBoy 543cc 1988	23 kW / 31 bhp	550 kg / 1213 lb	42 W/kg / 39 lb/hp
Holden FJ 2160cc 1953 ^[8]	45 kW / 60 bhp	1012 kg / 2250 lb	44 W/kg / 38 lb/hp
Suzuki Alto 796cc 2000	35 kW / 46 bhp	720 kg / 1587 lb	49 W/kg / 35 lb/hp
Land Rover Defender 2.4L 1990^[9]	90 kW / 121 bhp	1837 kg / 4050 lb	49 W/kg / 33 lb/hp
Toyota Prius 1.8L 2010 (petrol only)^[10]	73 kW / 98 bhp	1380 kg / 3042 lb	53 W/kg / 31 lb/hp
Bajaj Platina 100cc 2006^[11]	6 kW / 8 bhp	113 kg / 249 lb	53 W/kg / 31 lb/hp
Subaru R2 type S 2003^[12]	47 kW / 63 bhp	830 kg / 1830 lb	57 W/kg / 29 lb/hp
Ford Fiesta ECOnetic 1.6L TDCi 5dr 2009^[13]	66 kW / 89 bhp	1155 kg / 2546 lb	57 W/kg / 29 lb/hp
Ford Focus ECOnetic 1.6L TDCi 5dr Hatch 2009^[14]	81 kW / 108 bhp	1357 kg / 2992 lb	60 W/kg / 27 lb/hp
Ford Focus 1.8L Zetec S TDCi 5dr Hatch 2009^[15]	84 kW / 113 bhp	1370 kg / 3020 lb	61 W/kg / 27 lb/hp
Hummer H1 6.6L V8 2006^[16]	224 kW / 300 bhp	3559 kg / 7847 lb	63 W/kg / 26 lb/hp
Audi A2 1.4L TDI 90 type S 2003^[17]	66 kW / 89 bhp	1030 kg / 2270 lb	64 W/kg / 25 lb/hp
Mini (new) Cooper 1.6D 2007^[18]	81 kW / 108 bhp	1185 kg / 2612 lb	68 W/kg / 24 lb/hp
Toyota Prius 1.8L 2010 (electric boost)^[19]	100 kW / 134 bhp	1380 kg / 3042 lb	72 W/kg / 23 lb/hp
Ford Focus 2.0L Zetec S TDCi 5dr Hatch 2009^[20]	100 kW / 134 bhp	1370 kg / 3020 lb	73 W/kg / 23 lb/hp
Ford Focus 2.0L Zetec S 5dr Hatch 2009^[21]	107 kW / 143 bhp	1327 kg / 2926 lb	81 W/kg / 20 lb/hp
Fiat Grande Punto 1.6L Multijet 120 2005 ^[22]	88 kW / 118 bhp	1075 kg / 2370 lb	82 W/kg / 20 lb/hp
Mini (classic) 1275GT 1969	57 kW / 76 bhp	686 kg / 1512 lb	83 W/kg / 20 lb/hp
Subaru Legacy/Liberty 2.0R 2005^[23]	121 kW / 162 bhp	1370 kg / 3020 lb	88 W/kg / 19 lb/hp
Subaru Outback 2.5i 2008^[24]	130.5 kW / 175 bhp	1430 kg / 3153 lb	91 W/kg / 18 lb/hp
Smart Fortwo 1.0L Bradbus 2009^[25]	72 kW / 97 bhp	780 kg / 1720 lb	92 W/kg / 18 lb/hp
Ford Focus 2.0 auto 2007^[26]	104.4 kW / 140 bhp	1198 kg / 2641 lb	94 W/kg / 19 lb/hp
Mini (new) Cooper 1.6T S JCW 2008^[27]	155 kW / 208 bhp	1205 kg / 2657 lb	129 W/kg / 13 lb/hp
Kawasaki KLR650 Gasoline DualSport 650cc	26 kW / 35 bhp	182 kg / 401 lb	143 W/kg / 11 lb/hp
NATO M1030M1 Diesel DualSport 670cc ^[28]	26 kW / 35 bhp	182 kg / 401 lb	143 W/kg / 11 lb/hp
Tesla Roadster 2008	185 kW / 248 bhp	1235 kg / 2723 lb	150 W/kg / 11 lb/hp
GMH HSV Clubsport / GMV VXR8 / GMC CSV CR8 6L V8 2006^[29]	317 kW / 425 bhp	1831 kg / 4037 lb	173 W/kg / 9.5 lb/hp
Lotus Elise SC 2008	163 kW / 218 bhp	910 kg / 2006 lb	179 W/kg / 9 lb/hp
Ferrari Testarossa 1984	291 kW / 390 bhp	1506 kg / 3320 lb	193 W/kg / 9 lb/hp
Artega GT^[30]	220 kW / 300 bhp	1100 kg / 2425 lb	200 W/kg / 8 lb/hp
Lotus Exige GT3 2006^[31]	202.1 kW / 271 bhp	980 kg / 2160 lb ^[32]	206 W/kg / 8 lb/hp
Chevrolet Corvette C6^[33]	321 kW / 430 bhp	1441 kg / 3177 lb	223 W/kg / 7 lb/hp
Chevrolet Corvette C6 Z06^[33]	376 kW / 505 bhp	1421 kg / 3133 lb	265 W/kg / 6 lb/hp
Porsche 911 GT2 2007	390 kW / 523 bhp	1440 kg / 3200 lb	271 W/kg / 6.1 lb/hp
McLaren F1 GT 1997^[34]	467.6 kW / 627 bhp	1220 kg / 2690 lb	403 W/kg / 4 lb/hp
Thunderbolt	3504 kW / 4700 bhp	7 t / 15432 lb	500 W/kg / 3.28 lb/hp
Ferrari FXX 2005	597 kW / 801 bhp	1155 kg / 2546 lb	517 W/kg / 3.2 lb/hp
Ultima GTR 720 2006^[35]	536.9 kW / 720 bhp	920 kg / 2183 lb	583 W/kg / 3 lb/hp
Honda CBR1000RR 2009^[36]	133 kW / 178 bhp	199 kg / 439 lb	668 W/kg / 2.5 lb/hp
MTT Turbine SUPERBIKE 2008^[37]	213.3 kW / 286 bhp	227 kg / 500 lb	940 W/kg / 1.75 lb/hp
Honda RC211V MotoGP 2004-6^[38]	176.73 kW / 237 bhp	148 kg / 326 lb	1194 W/kg / 1.37 lb/hp
Thrust Super Sonic Car	82 MW / 110,000 bhp	10.5 t / 23149 lb	7812 W/kg / 0.2 lb/hp

[edit] Batteries

Battery type	Energy-to-weight ratio
Nickel hydrogen battery	75 kJ/kg
Nickel-cadmium battery	150 kJ/kg
Lead acid battery	180 kJ/kg
Nickel metal hydride	250^[39] (market) –980 kJ/kg^[40] (lab)
Lithium ion battery	~340 kJ/kg^[41] 1700 kJ/kg (lab)^[42]

[edit] Electric motors

Motor type	weight	power	Power-to-weight ratio
Himax HC6332-230	0.69 kg^[43]	2.2 kW^[43]	3.19 kW/kg
Hi-Pa Drive^[44]	120 kg	235 kW	1.96 kW/kg

[edit] Fuel cells

Fuel cell type	Power-to-weight ratio
PEMFC	967 W/kg (market) - 1,500 W/kg (lab)^[45]

[edit] Spacecraft solar panels

Panel type	Power-to-weight ratio
Current	~170 W/kg^[46]
Believed possible	~300 W/kg^[46]

The inverse of power-to-weight, weight-to-power ratio (power loading) is a calculation commonly applied to aircraft, cars, and vehicles in general, to enable the comparison of one vehicle performance to another. Weight-to-power ratio is a measurement of the acceleration capability (potential) of any land vehicle or climb performance of any aircraft or space vehicle.

[edit] See also

[edit] References

[0] [1]

[1] [2]

[2] [3]

[3] ttp://www.latimes.com/news/printedition/highway1/la-hy-125mbzbox21jun21,1,3672562.story

[4] ttp://www.forcemotors.com/media/downloads/DIESEL3SEATER.pdf

[5] ttp://balajiforce.com/threeWheelers.aspx?id=2

[6] ttp://www.popularmechanics.com/automotive/jay_leno_garage/1368287.html

[7] ttp://www.uniquecarsandparts.com.au/holden_FJ_technical_specifications.htm

[8] ttp://www.whatcar.com/Review/EditionCompare?newOrUsed=New&makeId=11729&modelId=11730&editionId=11781#tabsection3

[9] [4]

[10] ttp://www.autoindia.com/VehicleStyles/bike-car-details1086.html

[11] [5]

[12] [6]

[13] [7]

[14] [8]

[15] ttp://www.internetautoguide.com/car-specifications/09-int/2006/hummer/h1/index.html

[16] [9]

[17] [10]

[18] [11]

[19] [12]

[20] [13]

[21] ttp://www.whatcar.com/Review/EditionCompare?newOrUsed=New&makeId=9434&modelId=10026&editionId=31419&makeId1=&modelId1=&editionId1=&makeId2=&modelId2=&editionId2=#tabsection3

[22] [14]

[23] [15]

[24] [16]

[25] [17]

[26] [18]

[27] M1030M1 JP8/Diesel Military Motorcycle, Hayes Diversified Technologies, http://www.dieselmotorcycles.com/PDF/M1030M1_JP8_Diesel_Military_US.pdf, retrieved 2009-02-28

[28] ttp://www.whatcar.com/Review/EditionCompare?newOrUsed=New&makeId=2080&modelId=4102&editionId=4110#tabsection3

[29] Motor Authority » Artega GT now on sale

[30] [19]

[31] Lotus Exige

[MSN_Autos-32] "MSN Autos". http://autos.msn.com/research/vip/spec_Exterior.aspx?year=2008&make=Chevrolet&model=Corvette&trimid=-1.

[33] [20]

[34] [21]

[35] Honda CBR1000RR

[36] [22]

[37] [23]

[38] High Energy Metal Hydride Battery

[39] Improvement of Nickel Metal Hydride Battery with Non-foam Nickel Electrode for Hybrid Electric Vehicles Applications

[40] ttp://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_LiIon_CGA103450A.pdf

[41] Lithium Ion Battery Research

[rctoy-42] [24]

[43] [25]

[44] Low-cost light weight high power density PEM fuel cell stack

[rocket-45] Rocket and spacecraft propulsion By Martin J. L. Turner

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