ok found it..
care of mariogtr..
Nissan engine codes
There appears to be no rhyme nor reason to the Nissan engine codes.
The first letter descriptor is chosen to identify a style range and the second to delimit the type/application of the engine package.
R = 6 cylinder, closed deck.
B = Gasoline application using cast iron/nickle based block.
S = 4 cylinder, closed deck.
R= Gasoline application using sand-cast alloy based block.
K = 4 cylinder, closed deck.
A = Gaslone application using sand-cast iron based block.
Q = 4 cylinder, open deck.
R = Gaslone applcation using die-cast alloy based block.