[Editor: On 11/25/58, Ferry Porsche approved the development of a "new Super with 90 hp, design number 616/7", and the most powerful pushrod Porsche engine to date was introduced to dealers in June, 1959. The engine was, and still is, considered a very desirable 356 option, and increases the value of the car on resale. This has led to cases of 356s being portrayed as an S-90 even if they did not come that way from the factory. So the question is often posed, "How do I tell if the car I'm considering buying is really a Super 90?" The answer can be found below.]
Roy Smalley on how to identify a "true" S-90: There is no way to determine if a car was delivered as a S-90 just by looking at the car or the equipment--engine, tach, transmission, antisway bar--as all could have been changed at some point after the car was first purchased. (The same holds true for the 356C SC: tach, engine, transmission and the diameter of the rear torsion bar.
An S-90 is not distinguishable by the engine or any other equipment that is presently in the car, or data on the car. A legitimate chain of ownership or documentation is a way to identify the model, or a registration chain that identifies both the engine and VIN. The most persuasive is a document from the factory or some other factory source that ties the engine to the car as delivered. But nothing is absolute in the realm of 356. [Editor: the COA is a good place to start, but it is not always 100% accurate.]
I have two S-90. One is a clone with all the S-90 stuff, including tranny but built as a Normal. Another is an S-90 that has a correct later S-90 engine not original to the car.
Eric Cherneff on S-90 engine numbers: In published lists of engine numbers (see list below right), the end of a range is often given as xxx999 (for example, 802001 - 803999), suggesting that the full range of engines was produced. However, this is often not the case, and the upper limit of the range is lower than indicated. Harry Pellow documented some of the upper limits of engine ranges in "Secrets of the Inner Circle", but not for the Super 90.
While researching Super 90 engine numbers, I found a large break in the serial number range for which I could find no examples. Specifically, I found no engines between 803146 and 804038, a break of almost 900 units. Within the data I had, I could find no other gap even remotely this large. It has been subsequently confirmed to me that 803156 was the highest serial numbered Super 90 installed in a T5, and 804001 was the lowest Super 90 installed in a T6. There may exist a few engines with serial numbers beyond 803156 (but lower than 804001) that were built for warranty use, but they were not original to any given car.
Steve Heinrichs on when the first S-90's went into production: 356Bs began with VIN 108918, and the first S-90 engine, 800101 (see listing above right) went into a coupe on 7 September 1959. The second one went into another coupe the same day. A bit later, the second Roadster got one.
Amazingly, the S-90 list begins with production of chassis about 100 numbers later than the regular stuff rolling through. And, check this (dates are production dates):
VIN Build Date
108923 6 Aug '59 built with an unnumbered S-90 but engine removed
108924 7 Aug '59 got a S-90..number unknown...then a 1600S
108921 7 Sep '59 800101
108920 7 Sep '59 800102
86832 9 Sep '59 800104
108919 10 Sep '59 800103
108918 11 Sep '59 800105 then 19 Oct got a 1600S
152479 14 Sep '59 number unknown S-90
152512 18 Sep '59 800107 then 23 Oct 800110 then 800118
152527 22 Sep '59 800110 then 800007 then a 1600S
109157 28 Sep '59 800106 then 23 Oct 800113
109156 30 Sep '59 800111
109040 6 Oct '59 800113 then 15 Oct a 1600S
109333 22 Oct '59 800106
Then 11 more coupes and 2 more cabs through 30 Oct. A few more coupes in early Nov then no S-90s until an early Dec cab. Two cabs and one coupe through end Dec., then three coupes in Jan '60. There was an unnumbered S-90 coupe in early February as well as the next 2 Roadsters. Very few Roadsters then until 1961.
[Editor: Steve's information comes from his personal examination of the Porsche production records stored in the archives in Stuttgart. Those records are not available to the general public.]