bumpstart wrote:well, there is lots of changes between years and between markets,, in oz we dont see repus , or california spec stuff and so our info may not tee up correctly with american years and options
there is also differening and sometimes bastard combinations of inlet manifolds, some reversed, some cross ported primary to secondary , others as 4 individual runners and some with an anti buck butterfly below the throttle on only one primary
i will try and sum things up as best as i can recall of top of my head
i see early rx4 type housings, a little latter maybe than 74/75,,for several reasons
- cause i expect the 74-75 13b rotors to have 1757 stamped between rotor tip and bath
i expect if original,, the apex seals came with a long wedge piece ( longer than 76 upwards ) and a shorter main part of apex seal ,, and solid corner seals
i expect the early rx4 engine also to have a temp switch on top of the engine middle plate ( where some later engines have a vertical ACV /EGR passage )
expect quite a bit of change in markets and years in emissions spec 74-78 , and later some engines in some markets will get vertical ACV,, and others have it horizontally ( ACV on back of inlet manifold )
as far as the plates/ engines i have pulled down,, early 13bs use a letter to start the engine number,, and plates that went to 12a's will have a larger numeral
plates however readily interchange from early 13b to early 12a and vice versa
of the rx4 type 13bs ( with early and late fonts ) , i have seen end ( 2ndary* ) plates plates usually coded R5 or X or 3B
(* 2ndary here might be a missnomer,, there is a US market cosmo/rx5 manifold with reversed carb that uses the 2ndarys are the primary ports so to speak --- for the longer effective inlet runner ,, and that may just explain the unusual plate/ port combinations on some engines )
R5 2ndary port is 42 mm tall ( caliper top to bottom inside the port ) ,, and the R5 end plate feature all the through bolt holes and castings for the chain tensioner,, indications of earlier evolution
( later R5's are built with the short chain and no tensioner fitted , but still have castings )
X 2ndary port is 48 mm tall , is delete one through bolt on the rear,, and delete the chain tensioner positions , indications of a later evolution,, but curiously lacks the wedge over the oil filter dowel
3B i cant comment on as i currently dont have one to directly measure and compare, but i do recall at this point the rx4 engine ran all 4 ports the same size and thus this one should have the chain tensioner,, all the through bolts ,, is either 42 or 48mm in port height,, with centre plate to match ,, with small runners
middle plate wise,, we have several combinations again ,, some with overhead EGR /ACV, some with it below the primary runners in the horrizontal position,, and some with a water temp swtich on top instead
some of these have small ports,, some of these have large ports but small runners, and some have medium ports but large runners !!
of these ,, the most common early one is the R5,, slightly later is the R ,, and we can assume also there is an X and a 3B
( both that i havent seen yet, but i do know X exists )
there is also an N,, and an NO,, and a Y and a K that came in later 12a's ( and maybe 13bs )
again,, as IIRC --
the R5 and R middle plate port is 42 mm tall and has the tall runner AND the EGR horizontal port
the 3B middle plate must be the small runner in either 42 or potentially 48 mm with the overhead colant sensor and horizontal ACV
the X i dont know for sure , but believe its in US repus motors as middle plate
the NO is the nasty later plate that comes in most things jap,, and maybe cali , with a tiny 24mm high port , small runners and overhead ACV/EGR passage restricting further improvements
the N is a large port with horizontal ACV for same years ( 12a ) but other markets
the edit M and the K ( and i think maybe L ) are used on engines intended for possible HB cosmo use ( and potentially the US GSL-SE RESI engine ) and feature a casting for a middle engine mount between the exhaust pipes that some extractors will not fit
and so are found on 13b 6 port ( 83-85 ) , 12a 6p ( 1981 -85 ) and 12aT ( 83-87 )
the K is on the 12at ,, has horizontal ACV, small port ( just smaller than NO ) and small runners
the M i suspect is the 13b 6p,, is horizontal ACV , small runners and a smaller port again than K
L ( off distant memory ) i suspect is the 12a6p , horizontal ACV , small runner and the tiniest port ever , smaller than a pinky fingernail
