All M engines, apart from S65 and s85, share block designs from their standard road car counterparts.Originally Posted by Porscheman
The new engines in the current M5/6 and forthcoming M3/4 are no different and will be modified and tuned in the same way you have mentioned above. They have to be modified with stronger internals as they produce over 100hp more than the standard engine.
The S65 and S85 were different in that they were completley bespoke to the M cars they went into.