3Top,
There is a limit on maximum practical piston size in a turbodiesel, which in 4-cyl is approaching ~200BHP (that's why i only chose 4-cyls for the comparison). In theory you could take your 160 BHP 4-cyl Wilksch and double up on the number of pistons to make a 320 BHP V8. So the BSFC and kW/kg stay the same, although cost goes up linearly with power. In fact the 650 BHP (Cosworth/Mahle) VW R10 V12 diesel Lemans series machine boasts the highest specific power in a diesel car, and Ricardo/JCB have pushed further for a landspeed attempt - both are 4-stroke but are very secretive about weights. The same constraint will also apply to Avgas engines - it is all to do with combustion time.
Actually the SI diesel rotary does point to a possible future. You need to get the diesel to about ~600K before it will combust, but have to keep combustion below 2000K to avoid NOx. Running high boost, even with intercooling, will increase the inlet temp requiring a reduction in compression ratio. I had hoped to spark a nice technical debate on a rotary dedicated forum:
http://www.rotaryengineillustrated.c...topic.php?t=16
If you can design the crank mechanism to handle the pressure there is in principle no limit to the amount of turbo boost you can have. The same is true of Avgas, but the need to avoid knocking limits the possible efficiency. The ability to actually inject fuel during combustion is the main reason for my preference for diesels. My reservation about rotaries is entirely down to the combustion chamber fluid dynamics in such an awkward shape.
Mart