The 86 has a engine code of M44/07 and the 83's engine code is M44/02. But I have no clue what all the difference is between the two engine codes. Both have 150hp@5500 RPM. Both have a stroke of 78.9mm and a bore of 100mm. Both have a compression ratio of 9.5:1 and a DME fuel system. I found this info at
http://www.dimmer.net/hosted/944central/about/ just in case you're wanting to read more on it.