The JDM 12A Turbo.. Explained with pictures! (a lot of pictures..)
04-16-11 | 10:34 PM
#26
talking head
Joined: Apr 2008
Posts: 2,775
Likes: 14
From: Perth, WA, OZ
old thread ,, but useful pics ,, and i will ad my bit cause i have pulled down and installed my share of these
no1-- there is no active knock control on the 12at,, the ecu has been mapped carefully around the ping zone and there is no active retard from the dizzy without boost
n02,, there is 2 versions of the turbo used ,, the larger one has a 4 bolt rear dump pipe and is actually the lesser turbo
( will add a pic when i find it in the shed )
the variations are in the turbine wheel size,, and the 3 bolt dump turbo makes better power
i also suspect the ECU uses a 12v and not 5 V system on some of its senders,, but i cannot confirm that one
also the original 0830 injector is more like 690 cc at the rated system pressure ( 38 psi ) in some tests
PS
the exhaust port is the standard aussie market double cut exhaust port common to 6 port and later 12a's in oz and some other markets
- the tiny exhaust port on other housings i believe is a California spec thing
the 12a 6p housing uses the same font and ports and has the H casting and even the boss ( not drilled ) for the OMP injector
and so is a canditate to match a 12at housing with minimal mods if desired
the 12a 6p block also shares the exhaust side engine mount boss on the middle plate that the 12at and the 13b GSL-SE engine share
this is due to the specification that any of these motors can be fitted into the HB cosmo/ luce
no1-- there is no active knock control on the 12at,, the ecu has been mapped carefully around the ping zone and there is no active retard from the dizzy without boost
n02,, there is 2 versions of the turbo used ,, the larger one has a 4 bolt rear dump pipe and is actually the lesser turbo
( will add a pic when i find it in the shed )
the variations are in the turbine wheel size,, and the 3 bolt dump turbo makes better power
i also suspect the ECU uses a 12v and not 5 V system on some of its senders,, but i cannot confirm that one
also the original 0830 injector is more like 690 cc at the rated system pressure ( 38 psi ) in some tests
PS
the exhaust port is the standard aussie market double cut exhaust port common to 6 port and later 12a's in oz and some other markets
- the tiny exhaust port on other housings i believe is a California spec thing
the 12a 6p housing uses the same font and ports and has the H casting and even the boss ( not drilled ) for the OMP injector
and so is a canditate to match a 12at housing with minimal mods if desired
the 12a 6p block also shares the exhaust side engine mount boss on the middle plate that the 12at and the 13b GSL-SE engine share
this is due to the specification that any of these motors can be fitted into the HB cosmo/ luce
Last edited by bumpstart; 04-16-11 at 10:40 PM.
04-17-11 | 10:17 AM
#27
Moderator
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Joined: Mar 2001
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From: https://www2.mazda.com/en/100th/
you are correct the ECU IS a 12V AFM, like the gsl-se. i sold the ecus but i still have the afm
the exhaust ports in california are no different from the rest of the US. the ONLY difference we have in engines, is in 1980 we got an EGR valve, and the rest of the time the cold start assist is deleted.
i see what you're talking about with the exhaust port, but the OP is in norway.
also the cheater housing here was the N210-10-100 which is a euro 12A, it had 10 degrees more port timing. it was the hot ticket for the racers, until they got caught
the exhaust ports in california are no different from the rest of the US. the ONLY difference we have in engines, is in 1980 we got an EGR valve, and the rest of the time the cold start assist is deleted.
i see what you're talking about with the exhaust port, but the OP is in norway.
also the cheater housing here was the N210-10-100 which is a euro 12A, it had 10 degrees more port timing. it was the hot ticket for the racers, until they got caught
04-17-11 | 09:40 PM
#28
talking head
Joined: Apr 2008
Posts: 2,775
Likes: 14
From: Perth, WA, OZ
ok ,, here are some of my pics,,
sorry pics are my normal notorius quality
firstly,, the rare as 4 bolt rear 12at early turbo ,, alongside it is a later 3 bolt dump,, and a n236 exhaust manifold
the turbo is known as the HT-18-BM
sorry pics are my normal notorius quality
firstly,, the rare as 4 bolt rear 12at early turbo ,, alongside it is a later 3 bolt dump,, and a n236 exhaust manifold
the turbo is known as the HT-18-BM
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mattallac (11-27-19)
04-17-11 | 09:47 PM
#30
talking head
Joined: Apr 2008
Posts: 2,775
Likes: 14
From: Perth, WA, OZ
------------------------------------------------------------------
below is is an old post of mine where i have tried to label and quantify each 12a housing i have
exhaust port measurements are taken upwards from a flat bench
below is is an old post of mine where i have tried to label and quantify each 12a housing i have
exhaust port measurements are taken upwards from a flat bench
Originally Posted by bumpstart
1881-10-100a/3625-23-050 74-75 12a rotor housings
8871-10-100/150 76-79 12a
8341-10-100/150 80 california spec 12a
n201-10-100 81-83 usa
n249-10-100 84-85 usa
n210-10-100/150 (81-85?) euro 12a housing
n236-10-100 12a turbo housings
trying to order these chronologically as i see them ( and clarify the jumble above )
note if there is front and rear specific housings
then the rear? housing has the /150 end prefix instead of /100
this is how i piece them together,, there may be some errors and point them out if you see anything
--all measured from a flat bench
( provided in a form for all those without a degree wheel )
1881-10-100
1974-75
original font
smooth around the spark plugs
EGR/ACV port is the original banjo bolt through the sump style
EO=
EC=
---------------------
8871-10-100
76-79 12a
note the new mazda font , but with a 10 mm gap to the 12a cast letters
in between,, a blank casting strip where perhaps " automobiles " has been hurriedly deleted from the casting
late EO port ( high port )
EO= 82 mm ( approx )
EC= 104 mm
------------------------
N201-10-100
early EC port ( small )
note casting font has evolved to delete the delete casting so to speak
- still 1 cm gap
EO= 78mm
EC= 97mm
----------------------
N210-10-100 ??
late EC port ( large )
EO= 78mm
EC= 104mm
------------------
???
double cut port ( medium )
EO= 78 mm
EC= 102mm
--------------------
N249-10-100
final font ,, no gap in the casting to the 12a moniker
dimples and small shrouds around the spark plugs
H casting on top
early EC small port
EO= 78mm
EC= 97 mm
-------------------
N236-10-100
final font
spark plug dimples and shrouds
double cut port
and oil squirt location = 12at
double cut medium port
EO= 78mm
EC= 102mm
----------------------
so far missing from this list
N225 1981 12a 6p
( with the 225mm clutch if manual and with the funny shaped little front counterweights of the late ones )
which is out of bunch chronologically as its actually a s3 type motor
that japan released while everybody else still copped s2 type housings ( rotors and weights )
they have the H housing casting, dimpled area at the plugs, but importantly one of the shrouds is segmented
inside the rotors are marked NF or NR,, a give away for s3 rotors
and N231 1983 rx7
which should be visually similar,, with final font and dimples with H
8871-10-100/150 76-79 12a
8341-10-100/150 80 california spec 12a
n201-10-100 81-83 usa
n249-10-100 84-85 usa
n210-10-100/150 (81-85?) euro 12a housing
n236-10-100 12a turbo housings
trying to order these chronologically as i see them ( and clarify the jumble above )
note if there is front and rear specific housings
then the rear? housing has the /150 end prefix instead of /100
this is how i piece them together,, there may be some errors and point them out if you see anything
--all measured from a flat bench
( provided in a form for all those without a degree wheel )
1881-10-100
1974-75
original font
smooth around the spark plugs
EGR/ACV port is the original banjo bolt through the sump style
EO=
EC=
---------------------
8871-10-100
76-79 12a
note the new mazda font , but with a 10 mm gap to the 12a cast letters
in between,, a blank casting strip where perhaps " automobiles " has been hurriedly deleted from the casting
late EO port ( high port )
EO= 82 mm ( approx )
EC= 104 mm
------------------------
N201-10-100
early EC port ( small )
note casting font has evolved to delete the delete casting so to speak
- still 1 cm gap
EO= 78mm
EC= 97mm
----------------------
N210-10-100 ??
late EC port ( large )
EO= 78mm
EC= 104mm
------------------
???
double cut port ( medium )
EO= 78 mm
EC= 102mm
--------------------
N249-10-100
final font ,, no gap in the casting to the 12a moniker
dimples and small shrouds around the spark plugs
H casting on top
early EC small port
EO= 78mm
EC= 97 mm
-------------------
N236-10-100
final font
spark plug dimples and shrouds
double cut port
and oil squirt location = 12at
double cut medium port
EO= 78mm
EC= 102mm
----------------------
so far missing from this list
N225 1981 12a 6p
( with the 225mm clutch if manual and with the funny shaped little front counterweights of the late ones )
which is out of bunch chronologically as its actually a s3 type motor
that japan released while everybody else still copped s2 type housings ( rotors and weights )
they have the H housing casting, dimpled area at the plugs, but importantly one of the shrouds is segmented
inside the rotors are marked NF or NR,, a give away for s3 rotors
and N231 1983 rx7
which should be visually similar,, with final font and dimples with H
04-17-11 | 10:21 PM
#32
Moderator
iTrader: (3)
Joined: Mar 2001
Posts: 31,196
Likes: 2,825
From: https://www2.mazda.com/en/100th/
we've done this before yes?
in the USA, we got slight variations
i agree on the 74-75 big font, 1881 (1757 for a 13B).
76-80 i also agree on, 76-78 in the us it will say automobiles.
your N201 pic doesn't look like what we have, in the US the N249 and N201, were almost visually identical. we got the "lean burn" catalytic converter engine in 1981.
in 83 it got the N225 rotating assembly, beehive oil cooler; rear heater outlet turns into a T, 17mm oil pump.
in 84 it got the N249 rotor housings. http://www.jimrothe.com/mazda/84_tra...training_1.pdf
and the exhaust manifold changes so they can add a 3rd catalyst
ALL of the 76+ engines in the USA had the same port timing, the 74-75's close 10 degrees later on the intake and exhaust.
tedious, but in search of clarity
in the USA, we got slight variations
i agree on the 74-75 big font, 1881 (1757 for a 13B).
76-80 i also agree on, 76-78 in the us it will say automobiles.
your N201 pic doesn't look like what we have, in the US the N249 and N201, were almost visually identical. we got the "lean burn" catalytic converter engine in 1981.
in 83 it got the N225 rotating assembly, beehive oil cooler; rear heater outlet turns into a T, 17mm oil pump.
in 84 it got the N249 rotor housings. http://www.jimrothe.com/mazda/84_tra...training_1.pdf
and the exhaust manifold changes so they can add a 3rd catalyst
ALL of the 76+ engines in the USA had the same port timing, the 74-75's close 10 degrees later on the intake and exhaust.
tedious, but in search of clarity
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