Quote:
Originally Posted by Flieger
According to Fere, 87.5mm and 86.7mm cylinders were Biral. He says that 87.5mm was the maximum Biral cylinder diameter the factory could use with enough reliability.
For the 2380cc engine, 87.5mm bore Biral cylinders were used with the 66mm stroke crankshaft. For 2494cc, 86.7mm with a 70.4mm stroke crankshaft was used.
Porsche wanted to use the short stroke 66mm crankshaft for better revving and less vibration so they used the Mahle Nickasil technology already tried on the 917. This was the 89mm bore cylinder with the 66mm stroke crankshaft.
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Here is an early document stating the use of chromal...
FWIW I also have sets of 86.7 and 87.5 Mahle cylinders that are nickasil.
I am not arguing that Biral was not used because I wasn't around at the time. But all of the factory documentation that I have come across stated the use of either of these two types.
Also, Nickasils were introduced in 1971 which would put the use of them close to when the ST's were being actively raced.