Very true nothing too uncommon for bike engines these days
but if an NA 1.6L can make 300hp then thats crazy hp yet the
AM is unique as its a high hp NA engine thats not boosted.

Simon already adapted a late Honda black hawk head on an A12
not easy alot of work but for now the 8v A series head
with boost is doing the honours needed.

Plenty of Twin cam head conversions done on the A series
by now but no one offers a kit anymore like Rob did.
Mazda b6 heads are still commonplace and popular support
aftermarket s/ tuning thats hard to beat.

160kws atw from a b6 is quite nuts for a miata yet cannot
image what that would be like on a 1000/1200! yet it is
possible boring an A15 to 78mm to suit the B6/Z5 bores


The Ford Kent head for your search on OHV possibilities
with little capacity 158hp atw that non-crossflow Kent
Seems to have better port angles and layout than Nissan A
http://www.rsmotorsport.com.au/forums/viewtopic.php?f=11&t=2884

Cast iron head below with 1500cc and 163hp a@ 8000rpm
http://www.rsmotorsport.com.au/forums/viewtopic.php?f=11&t=2884
Yet Nissan A series has better combustion chamber design