The German Way: DIN Horsepower Ratings

Since we’ve been talking more about European cars this year, we have been making frequent references to “DIN” power ratings. We wanted to be sure everybody is clear on what that means.

DIN is short for Deutsche Industrienorm (German industry standard), a standard issued by the German national institute for standardization, now called Deutsches Institut für Normung and abbreviated DIN. Among other things, the agency sets standards for how the horsepower and torque of automobile engines should be measured: Deutsche Industrienorm 70020.

As you might imagine, the standards of DIN 70020 are specific and very strict. Unlike the SAE gross standards used in the U.S. and Great Britain for many years, the DIN standard requires power to be measured with standard intake, exhaust, and accessory systems in place. DIN horsepower ratings, therefore, are comparable to the modern SAE net rating system, although they are usually reported in metric horsepower (sometimes referred to as Pferdestärke, the German word for horsepower, and abbreviated PS), rather than mechanical horsepower. One mechanical horsepower is about 745.7 watts, whereas one metric horsepower is about 735.5 watts; therefore, 1 PS equals 0.986 horsepower. Because of that and because DIN horsepower ratings are calculated with the engine in “as-installed” condition, they are always lower than gross ratings. (The peak engine speeds for DIN power and torque ratings are often lower, as well, reflecting the effects that mufflers, air cleaners, and accessories have on the engine’s power curve.)

Until the early 1970s, it was not uncommon for cars sold worldwide to have two power ratings — one DIN, one gross — largely as a concession to the salespeople. A Porsche 356 Super 90 engine, for example, was rated 90 hp DIN, but 102 hp SAE gross. Adding to the fun was the fact that, as we’ve previously discussed, SAE gross numbers sometimes bore very little relationship to actual output. This did NOT necessarily mean that the U.S. or British engines were more powerful than their European counterparts, simply that their ratings were figured differently.

So, before you write us to complain that we have maligned your favorite car by saying it had less power than advertised, please consider the source, and whether that source was quoting SAE gross, SAE net, or DIN figures.

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2 Comments

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  1. I got into a big argument with a guy (yes, online) about whether cars in the UK are rated at the wheels or the crank.

    I said crank, but he claimed companies’ advertised ratings in bhp were at the wheels.

    Do you know the answer?

    Every other rating I’ve seen is for the engine, at the crank, with various test conditions (hence gross, net, or DIN). I’d prefer the published data were at the wheels, as it’d keep manufacturers more honest as to available power after drivetrain losses.

    1. I have never seen any manufacturer officially list wheel horsepower; it’s always at the flywheel. (There were erroneous reports in 1971-72, when net ratings came into use, that net ratings were at the drive wheels, but that’s not correct.)

      I think mostly it comes down to the fact that the numbers would be a lot less impressive. It would also illustrate the comparative efficiencies of different transmissions, which is something I suspect a lot of manufacturers would prefer to avoid if they could.

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