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Plus I get confused when watching Top Gear / 5th Gear because I never know if they are talking to the wheels or to the flywheels. For example, this past weeks Top Gear they road test the new GTO and he says it?s 302 BHP. Well here in the USA it?s advertised as 350hp, but that # is to the flywheel, not the wheels. Are all the HP #s on those shows to the wheels?
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at the flywheel,unless specifically stated otherwise.
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Usually it is the horsepower available at the crankshaft in UK.
However years ago we used to use a gross measurement of HP which was the power the engine developed without any ancillaries connected - fan, water pump, alternator etc. When Europe changed to using the nett figure i.e. with those items connected, the USA continued to use the gross figure; I don't know if they still do. I had an Audi which had a quoted HP of 115gross, 100 nett. SAE and DIN if my memory serves me right.
Even so with the ease that engine outputs can be changed by electronics it is not unusual for manufacturers to sell cars with varying states of tune in different countries. Or even in the same country.
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Whatever the case, it's largely academic. What you really want to know is acceleration time 0-60mph, 30-70mph etc, 1/4 mile standing start time, top speed etc etc. In other words, you want to know performance characteristics that you can relate to. The max BHP on its own is but a small part of the full story.
--
L'escargot by name, but not by nature.
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Cardew is spot-on, the US figures are SAE and Europe use DIN. SAE allow the manufacturer to remove the water pump, alternator, cooling fan etc creating a higher figure. All figures are measured at the flywheel (or crankshaft). For power at the wheel as measured on a rolling road there are transmission losses to work in depending on the drive configuration.
In the days of the US muscle car, the manufacturers would tweak the engines for test to make them more impressive, 500 hp (SAE) might be a 400 bhp regular engine with a raised compression, better exhaust, bigger carb, advanced timing etc, not very useable on the road but good power at peak revs. Then knock off the 15% approx to make it DIN power....
Jaguar did the same with the E-Type Jaguars they suipplied for road tests (the 3.8 litre, 4.2 litre and 5.3 litre ALL made about 270 bhp, but only one was almost truthful) and Austin did it in the 1980s with the Maestro Turbo to get good performance figures in the magazines.
Gareth
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I found this site
neptune.spacebears.com/opine/horsepwr.html
which answers many of my questions and largely discounts your comparison of SAE and DIN. I thought it was interesting.
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Apologies, I was talking about gross SAE horsepower so my comments are correct! If SAE and DIN are so similar then where's the missing 50 bhp? Power at the wheels is almost never quoted in magazine features (unless the car has been modified and taking the engine out of the car and dyno testing is too difficult) and never in manufacturers' brochures.
Gareth
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On some cars I think the figure comes from the imagination of the marketing men. The then get the tech staff to specially prepare an engine and test it on a cold day with high atmospheric pressure so they can sqeeze every bit of power out of it. Others are a bit more honest.
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After a bit of digging I found that the German PS horsepower is corrected to 68 degrees Fahrenheit and 30.0 inches of Mercury of dry-air pressure. Meanwhile, the Americans corrected to less dense conditions at 77 degrees and 29.3 inches of dry air. The result was that the DIN corrections produced slightly higher numbers than the American method did. Combined with the difference between hp and PS, SAE horses are actually about five percent bigger than DIN ponies. That's why a 1978 Porsche 911SC, which was equally powerful in the U.S. and Europe, was rated at 172 SAE net hp and 180 DIN PS.
In the mid-'80s, the European carmakers adopted a new European Union power-measuring standard, which standardized the test conditions as the SAE net values. There are still minor differences in the correction formulas, but generally, the power calculated by SAE net and EU methods should be within 0.5% of each other.
However, in order to meet the U.S Low-Emissions Vehicle standard, the U.S spec engines may have a different intake manifold and a larger, free-flowing catalyst than the European version? All this isn't going to find 50 hp on your Nissan 350 though.
Gareth
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But at the end of the day, what matters is power/weight.
My vintage car, may only have 40 BHP (flywheel) but it weighs less than 8cwt. That is 100 BHP/ton, something that some smaller cars these days only just reach.
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My experience trying to compare ars in the UK and Oz is that what is nominally the same car with the same engine capacity do not match.
Due to local market conditions, fuel quality, local emissions requirements the engine fitted into an otherwise identical car can vary substantially. This may be a different camshaft, or even a complete cylinder head or as simple as a different ECU mapping.
I know that Subaru put different engines in the Liberty/Legacy for different markets.
regards
Ian L.
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