GT 500 problem

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Re: GT 500 problem

Post by Pierre » Thu Aug 20, 2009 5:27 pm

in europe most car manufacturer give the power at the wheels

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Re: GT 500 problem

Post by knightendo77 » Fri Aug 21, 2009 3:31 am

Yes, and somehow I think 'Top Gear' know what they're doing. Solid Snake you're trying to say they measured it wrong, well I'm sorry but they didn't. Brake Horse Power is measured this way, simple as that. This is a professional motoring show, using professional equipment used by professional engineers. To try and say they don't know how to measure BHP properly is ludicrous! They've done it this way for years, and that's because that's how it's measured, not just in Europe but worldwide. Ford were caught out, simple as that.
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Re: GT 500 problem

Post by Solid Snake » Fri Aug 21, 2009 7:57 am

Manufacturers that refer to brake horse power do not refer to power at the wheels. Brake horse power is:

Brake / net / crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft)

minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.), equals

The type of horse power you both are referring to is called effective horse power:

Effective, True (thp) or commonly referred to as wheel horsepower (whp)


Top Gear tested the effective horsepower, they even say something to the extent of "measuring the power that actually gets to the wheels". Which is correct, but it is NOT the way this car was rated by its manufacturer and it is not the standard to rate a car in this way. The standard is brake horsepower, also known as horse power from the crankshaft... meaning that the loss of power through the wheels and suspension is not factored in.

Again, I do not say they measured it wrong, infact they measured it correctly... but they stated it as if the car should have had 500 hp at its wheels which it simply is not correct because of simple car mechanics and characteristics as explained above. Top Gear is a great show... but it's car entertainment, meant to entertain people which it does perfectly :good: I love it. And this item with the Mustang though truthful to the extent that yes the car has less horse power at the wheels than straight out of the engine (like any car) was exactly what I just said, entertainment.
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Re: GT 500 problem

Post by Solid Snake » Fri Aug 21, 2009 8:14 am

Grrrr, I wanted to edit my post to add some better detailed reference material but I could not edit it anymore... so I have to repost, sorry...

Manufacturers that refer to brake horsepower do not refer to power at the wheels. Brake horse power is:

Brake horsepower

Brake horsepower (abbreviated bhp) is the measure of an engine's horsepower without the loss in power caused by the gearbox, generator, differential, water pump, and other auxiliary components such as alternator, power steering pump, muffled exhaust system, etc. "Brake" refers to a device which was used to load an engine and hold it at a desired RPM. During testing, the output torque and rotational speed were measured to determine the "brake horsepower". Horsepower was originally measured and calculated by use of the indicator (a James Watt invention of the late 18th century), and later by means of a De Prony brake connected to the engine's output shaft. More recently, an engine dynamometer is used instead of a De Prony brake. The output delivered to the driving wheels is less than that obtainable at the engine's crankshaft.


Top gear used a dynamometer which is the most common way to measure a cars horse power at the wheels, not the engine.

In the case of an engine dynamometer, power is measured at the engine's flywheel (i.e., at the crankshaft output). With a chassis dynamometer or "rolling road", power output is measured at the driving wheels. This accounts for the significant power loss through the drive train. As an example, an early-production BL Mini 850 cc (51.9 cu in) engine produced about 34 bhp (25.4 kW) at the flywheel, of which only 18.2 bhp (13.6 kW) reached the driving wheels.[citation needed]

In general:

Nominal is derived from the size of the engine and the piston speed and is only accurate at a pressure of 7 lbf/in².

Indicated or gross horsepower (theoretical capability of the engine)

minus frictional losses within the engine (bearing drag, rod and crankshaft windage losses, oil film drag, etc.), equals

Brake / net / crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft)

minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.), equals

Shaft horsepower (power delivered to and measured at the output shaft of the transmission, when present in the system)

minus frictional losses in the universal joint/s, differential, wheel bearings, tire and chain, (if present), equals

Effective, True (thp) or commonly referred to as wheel horsepower (whp)


Source: Wikipedia.org.


Top Gear tested the effective horsepower, they even say something to the extent of "measuring the power that actually gets to the wheels". Which is correct, but it is NOT the way this car was rated by its manufacturer and it is not the standard to rate a car in this way. The standard is brake horsepower, also known as horse power from the crankshaft... meaning that the loss of power through the wheels and suspension is not factored in.

Again, I do not say they measured it wrong, infact they measured it correctly... but they stated it as if the car should have had 500 hp at its wheels which it simply is not correct because of simple car mechanics and characteristics as explained above. Top Gear is a great show... but it's car entertainment, meant to entertain people which it does perfectly :good: I love it. And this item with the Mustang though truthful to the extent that yes the car has less horse power at the wheels than straight out of the engine (like any car) was exactly what I just said, entertainment.

Sorry to make this a big post, but I just want to make it as clear as possible so that readers would understand the various different measurement types.
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Re: GT 500 problem

Post by Pierre » Fri Aug 21, 2009 1:05 pm

so a GT with 300HP is less in effective power? :?

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Re: GT 500 problem

Post by Solid Snake » Fri Aug 21, 2009 3:13 pm

I think my story explained itself. Yes all cars make less power at the wheels than what they do out of the engine. Like the example that wikipedia uses with the Mini ... all cars similarly lose power through the suspension and gearbox... it is common automotive mechanics. As normal as ABC really... For fun people should just take their factory stated brake horsepower and subtract 15% off it and you can see how much power your car actually produces at the wheels, given of course your car was maintained nicely and the engine and transmission are in good order, if they are not the number will in reality be lower than what you calculate.

To make it clear one more time, manufacturers state and measure brake horsepower... which is measured at the crankshaft of the engine, that is the power we see on the specification sheets, manuals and magazines... effective or true horsepower is not used as a certified measure in car specifications, but effective horsepower is less than brake horsepower because the power goes through the gearbox, oils and suspensions etc. etc. before it reaches the wheels, which means power is lost due to friction and such. Thus it is lower. It happens on all cars... Only cars that would not have it are cars that have their power directly transferred too the wheels without a gearbox between the engine and the wheels, but such cars do not exist.

Sorry to sound like a car geek... but hey I am :D
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Re: GT 500 problem

Post by tamatt27 » Fri Aug 21, 2009 7:18 pm

Just to add a little to what Solid's talkin' about. There's HP (Horsepower) and Wheel Horsepower (RWHP on a rear wheel drive car). Horsepower is measured at the crankshaft to set a baseline for what the engine is actually producing. RWHP is measured,accuratly, only on a dyno.
On a dyno, RWHP can be measured because the car is physically strapped down onto the machine with the drive wheels on the rollers. The rollers provide a given resistance and the car is accelerated on the rollers. The dyno software determines the RWHP this way. The difference between HP and RWHP is the power that's lost through the transmission (auto's rob more power because of the fluids and clutches slip), driveshaft, rearend differential and axles.
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Re: GT 500 problem

Post by knightendo77 » Mon Aug 24, 2009 2:23 pm

I'm not going to get involved in an argument here, but to say that 'Top Gear' is only an entertainment show and so somehow that means its findings should be seen as "entertainment" and not fact isn't on! Fact of the matter is, the GT500 Mustang is nowhere near as powerful as Ford make out. To lose that amount of HP from engine to wheels is ludicrous. As much as I like Ford cars and like the look of the Mustang the company has a habit of overselling their cars' performances. Even the ones who made the KR pilot had to add a bigger engine and a huge crap load more HP just to get it to do what they wanted it to!

Hopefully Ford have knocked that on the head though with this new Mustang.
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Re: GT 500 problem

Post by Solid Snake » Tue Aug 25, 2009 8:32 am

The difference in power is explained above, the use of a rolling road like Top Gear did gives a lower figure than the actual measuring of Engine power... as that uses a different method to measure... but regardless... Ford actually has the reputation historically of underrating the performance versions of their cars, and I am talking of engine power measurements... not rolling road measurements... but again for the sake good spirit let us not argue about these points, no real reason to argue :wink: .

As for the KR pilot... the reason of tuning the cars was simple, the car that was used was a normal base model... For the car to be able to look and go as fast as a real KR (which was not even out at the time of shooting) they had to dress up the car and tune it accordingly... they did not tune a Shelby, they tuned a base Mustang. But then again that seems perfectly reasonable to me... to tune a $23.000 car in order for it to perform like a $80.000 + car.

For the record however, back in the old days, the Trans Am had the exact same treatment... the "underwhelming" engine that came with the car was pulled for a more powerful model for shooting the scenes.
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Re: GT 500 problem

Post by knightendo77 » Tue Aug 25, 2009 10:20 am

You're right, it's not something we should be arguing over ;)

My only point I wished to stress is that while 'Top Gear' is an entertainment show, it's factual data is always correct. Believe me, I work in BBC Information and we've been in touch with the producers on several occasions when manufacturers have accused them of false information and every time they've been able to produce a huge list of proof from independent sources... it gets quite funny after a while ;)
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Re: GT 500 problem

Post by Pierre » Wed Aug 26, 2009 3:16 am

in france sadly a gt coste 60000$ a gt 500 100000$ and i saw a KR for 170000$

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Re: GT 500 problem

Post by Solid Snake » Wed Aug 26, 2009 9:16 am

knightendo77 wrote:You're right, it's not something we should be arguing over ;)

My only point I wished to stress is that while 'Top Gear' is an entertainment show, it's factual data is always correct. Believe me, I work in BBC Information and we've been in touch with the producers on several occasions when manufacturers have accused them of false information and every time they've been able to produce a huge list of proof from independent sources... it gets quite funny after a while ;)
I don't dispute that at all! I agree the information is correct, it is just how the general public receives it. Top gear says it is less power that comes through the wheels and that is correct, as like I explained it is common automotive knowledge. And that is my problem, the car does not produce less power, it produces exactly the power it is billed to produce... 500 hp... out of the engine and not at the wheels. That is what I want to be clear about :).

And yes I remember how some manufacturers were angry :D. Rover was one of them :D CityRover thing was funny!
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