I went back to look at the Tech specs again and they are a little of a mystery. I don't believe the 72-73 cars were heavier than the 74-77s, but they are all listed as DIN weights, although only the 72-73 uses the term 'empty weight'. The difference must have to do with features and fluids.
Here is an article on DIN I found that points out some interesting facts about DIN.
Written by Aaron Severson
Tuesday, 24 March 2009 13:14
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. That institute, known between 1926 and 1975 as Deutsche Normenausschuss (DNA), is now called Deutsches Institut für Normung, also 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, it 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 Pferdestärke (literally, "horse strength," but generally referring to metric horsepower), rather than mechanical horsepower. One mechanical horsepower is 746 watts, whereas one metric horsepower is 736 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. Adding to the fun was the fact that, as we've previously discussed, SAE gross numbers were often dictated more by the marketing staff than the engineering department, and sometimes bore little relationship to actual output. This did NOT 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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Originally Posted by CurtEgerer
