[quote=Eurostyle;1135256] i dont understand why they had to use it on the road version, OTHER then the limited # needed for homologation! Is that clear...QUOTE]
Because the original M3 wasn't conceived as the tarted up 3 series for men with big wallets and short boners that the later ones were.
Early M cars were essentially road cars with racing engines. All were very low production. The M3 was built as a homogolation special and that's all.
The E30 M3 has basically an M10 block with a head design adapted from the 6cyl in the M5/M6 (and before that M1).
...and they didn't have a better 6 at the time. The 2.5l six had 168hp vs the s14's 210hp in euro tune. The 3.5l six had only 10hp more but was heavy and unbalanced the car. The M5/M6 motor had more hp but was a shoehorn fit and again too heavy. The M50 motor was 5 years away and the S50/S52 nearly a decade. (And the M50 still had less hp.)
What makes the M3 great is its balance. The S14 won't beat any 16 year olds in their camaros away from a stop light, but it kicks ass on twisty roads and that is the point.