Up to 86 had >> straight LSD
Post 86 had >> ASD with LSD
From 88 was 2.5 - reinforced block, in-house cylinder head, different internals, duplex timing chain, different injection widgets,
Ride height adjustable suspension was optional (as per the standard Evo models.)
Just lots of little tweaks really.
Mate of mine has a 2.5-16v and whilst its undeniably nice, its no faster than the 2.3-16v (not on the road anyway) and it lost a lot of the 2.3-16v rawness of character