2.4L or 2.7L?

I have a '70 911 Coupe that has what appears to be a 2.4L engine (the gold decal on the fan says 142,8 cubic inches and the MFI fuel pump indicates a 2.4S on its housing stamp). The engine serial number is 6332186 and the casting number is 901 106 101 5R. The engine case and fan are red. My question is that this car seems to have great power for a 2.4L. A previous mechanic indicated that the motor had been modified to a 2.7 or even a 2.8L. Is there any way to tell from the outside if the displacement has been modified on this motor?

The engine serial no. indicates that it is a 1973 2.4S version. However, it may have been modified/uprated over the years & it is very difficult without stripping the engine to tell exactly what may have been done to it.
Andy ('69 911E)

Thanks Andy!

Do you have the serial number legend that tells you which numbers mean what?

The factory publication commonly called a 'spec. book' has the decoding information on p. 9:

1st digit '6' for a 6-cylinder powerplant ...

2nd digit '3' for an 'S' engine ... [1=T, 2=E, 5= carbureted 'T', 6= RS 2.7]

3rd digit '3' for 1973 model [2= 1972 model]

xxxx = sequential engine number, so your 2186 was a very late '73 production, one of the last 'S' engines ever built!!!

The 90 mm Nikasil or Alusil cylinders 'look' different than the 84 mm Biral 2.4 cylinders, but it would be very hard to tell you the appearance differences ... try looking underneath a 2.7 to get a clue.

There are special gauges that can measure the swept displacement of an individual cylinder to within a cc or two ... you might inquire at a hot-rod or racing engine shop, if you have one locally.

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Warren Hall
1973 911S Targa

If you are still interested in identifying the cylinders used in your engine's rebuild, here are the differences:

The 84 mm cylinders in a 2.4 are 'Biral,' with aluminum fins cast around a cast-iron sleeve, and ALL Biral cylinders have fins that are 'gapped' ... there are 'notches' or gaps in the fins at certain places all around the circumference of the cylinder.

All of the 90 mm cylinders in 2.7's have fins that are continuous all the way around the circumference of the cylinder, with NO gaps or discontinuity at all!!!

So, if you get down on the ground at the back of your engine ... look up at the cylinders: gaps in fins = 2.4, continuous fins = 2.7

Good luck!

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Warren Hall
1973 911S Targa

Perfect! Thanks Warren.