The man at the request Rollo Tomassi Audio Conference finally available now
Automotive specifications are a lot of car and driver in the history of 51 years, the number that gets almost Attention everyone, of course, is power, but power is not as accurate a number as you might think.
Proves that there are many ways to measure engine power, and they produce different results put an engine on a dynamometer apparatus used to measure the power and you could get a wide range of power figures depending on the how the engine is configured, for example, an open exhaust system will allow more air to circulate through the engine of a restrictive exhaust, and thus produce more power.
It's just one variable among others, so that the Company SAE Automotive Engineers published a protocol power measurement It's called SAE J1349, and was updated in 2004 to fill gaps.
Thus, the rules have changed a bit, for example, the power steering pump that cuts power should now be installed on the engine when the engine power measure if it is part of normal automakers vehicle equipment spend gradually to the SAE standard, and has resulted in lower power ratings shown for some cars particular note Toyota 3 0 liter V-6, which now produces 190 horsepower under the new S20 standard less power than its claim to the old procedure.
A new twist to the power standard is a practice called certified SAE Under this optional program, a car manufacturer allows a third party witness designated CAS to verify that an engine produces the announced figures engines that have undergone this procedure are SAE certified badge.
Because of slight differences in the dimensions of the engine components that naturally occur during mass production the compression ratio could be a tad higher in an engine over another can lead to two identical looking engines making slightly different power, SAE allows a tolerance of one percent of the number that the witness observed and rated power that a manufacturer chooses to publish, for example, as Senior Director of DaimlerChrysler SRT powertrain, Pete Gladysz Dodge Failed its V-10 Viper to 510 horsepower, although a V- randomly selected 10 which has been torn from the assembly and broken in the usual cycle DC developed 512 horsepower line on the track dyno for the control sometimes referred to a group of components are located at the outer edge of manufacturing tolerances, and the combination hurts the output of MOTEU r sometimes they help the difference 0 to 4 percent between actual output V-10s and its rating is well within the SAE all owable tolerance band In fact, Dodge could have assessed the engine at 517 horsepower and reached one percent tolerance SAE we prefer to offer more than we promise, said Gladysz.
Interestingly, the new SAE standard is closer to the European procedure, which is EEC 80 1269 There are minor differences, for example, the exhaust configuration and specified fuel quality requirements vary, and they may have a effect on power, but we are talking about small differences, which is perhaps a less-than-one percent of change.
There is also a difference of one unit between SAE and ECE In the US, we use the system of imperial units for things like the length, volume and power Think foot, cubic inch, etc. In Europe there is the centimeter metric and English-liter power unit is the power, or HP the measure equivalent to power is for PS Pferdest keyless entry which is German for horses.
Because we define different units, a PS does not match HP HP describes about 1 4 percent more power a PS PS 0 x 9863 hp.
The point of all this is to tell you how we come to power ratings you see in our specification panels In most cases, we simply print the manufacturer number gives But sometimes when we have a first glimpse of a European car, for example the figure of power we get from the manufacturer is PS a good example is the BMW M5 BMW said the V-10 produces 507 PS engine for our range of specifications, we converted 500 hp 507 x 500 0 9863 Some time later, BMW released the SAE figure and quoted 500 hp In the end everything matched.
But it wasn t that simple with latest Porsche's 911 When we previewed the car Upfront, July 2004, Porsche said the three 6-liter flat-six have 325 PS We have conscientiously conversion and printed 321 hp Then a few months later, Porsche released the SAE figure and says the new 911 makes 325 hp, 4 hp on our number.
When asked about this discrepancy, Porsche responded cryptically that its engine delivered 325 hp, which perhaps suggests that the company slightly underestimated his engine in a similar way that Dodge had made in Example V-10 previously mentioned Regardless of what Porsche said, we continued printing 321.
Porsche is not unique in this case Audi also says the same numbers and PS hp However, Audi says retunes its engines for the US market, and why the engines were identical and HP PS Note Each company has its own procedure European manufacturers like BMW, Mercedes and Ferrari do the conversion in the same way we do as in the example above BMW M5.
Since this question was raised in the last few years we have been taking note of the procedures of each company and make the conversion, if any, but after much debate, we decided to change our system and use the manufacturer provided assessments hp We want to avoid the confusion that can occur when our figure published by HP is different from that seen in car advertisements or brochures Knowing that engines can produce slight variations in power than one percent tolerance, and remember that there is a small difference between SAE and ECE test protocol, we will resist now haircut and create unnecessary confusion on some horses.
Of course, there Sá difficult call, but if you can not agree, please try to keep in mind that we also provide information that is far more valuable than the figure hp know, the results of performance After all, the only reason to ask how the power of a car is to make a prediction on how it will interpret the forecasts say less than half of the story, and why we will continue to rely on our test equipment.
Larry Webster Horsepower Confusion and column resolution Car and Driver, power, confusion, conductor.