already itching for another engine build, old school vets input appreciated
10-19-11, 10:26 PM
#1
already itching for another engine build, old school vets input appreciated
some may know that a few months back i finished my ported S4 6port 13B into my FB, and all is going well with the exception that i will hafta pull my front cover this saturday and replace my blown front cover o-ring 
the other day, as i was digging around at my shop looking for another o-ring from prior gasket sets, i repeatedly re-found parts that i had aquired from day past, and started getting ideas for the next engine build....and the wife is not gonna be happy :O
the first treasure i found on a tool cart in the corner was an older spanish built Weber 50DCO/SP with some 42mm chokes, along with my old holley red fuel pump and aeromotive regulator... not bad for starters. still not finding my old gasket set, i continued skulking around. next i re-found my old mock up engine block from a few years back (12A housings and irons held together by a handful of tension bolts) i pulled the block apart and looked inside and remembered that those housings were my good pair aquired from several 12A tear downs, with virtually no flaking to speak of :O. it seems that im on a roll so far, why stop there? i continue digging around, completely forgetting about my original intentions, and my eyes grew wide as i saw 3 large flat boxes sitting next to some old irons. i opened them up and they contained what i thought
a set of irons i bought years ago, and "R5" front, and "Y" intermediate and rear irons that were Mazda Factory refurbished and renitrided...essentially brand new in the eyes of Mazda.... ---back story--- apparently a while back, after mazda already discontinued the production of pre-86 irons, they still needed a supply for factory reman'd motors that were requested here and there. mazda did the only thing they could at the time, which was buying back old 12A's from salvage yards, dismanteling them, and refurbishing the irons. mazda spec'd them, resurfaced them and then re-nitrided them and either built reman engines or sold off left over stock. luckily i found a full set (tho not matched for production/casting runs) Lastly, a few feet away i also saw a pair of S3 12A rotors, counterweights and E-shaft.
so now in my hands i (re)have...
Weber 50 DCO/SP w/ manifold/pump and regulator
a pair of excellent 12A housings
Factory "new" 12A irons
and a full S3 rotating assembly
this engine wont be an immediate build, but will be done over the next several months as i aquire seals and parts under the radar of.... the wife
im leaning heavily towards a full bridgey regardless of the route i take, and im also leaning towards using some ALS 1 piece ceramic seals... that being said, this is where my build ideas are branching of in 2 different directions and would like some input/suggestions
1) should i build a pure 12A bridgey?
or...
2) I have a friend who works at a machine shop and im considering having him mill a set of either 13B turbo FC housings i have, or some FD housings to accept coolant o-rings for use on pre-86 irons, and picking up a S5 NA rotating assembly, and ultimately building a nasty 13B bridgey
...and for the old school vets, what kinda meat do i have to work with for porting in the "Y" and "R5" irons? i think i remember reading a while back that the "R5" have more material to work with, but again, im not sure. any advice will be much apreciated
the other day, as i was digging around at my shop looking for another o-ring from prior gasket sets, i repeatedly re-found parts that i had aquired from day past, and started getting ideas for the next engine build....and the wife is not gonna be happy :O
the first treasure i found on a tool cart in the corner was an older spanish built Weber 50DCO/SP with some 42mm chokes, along with my old holley red fuel pump and aeromotive regulator... not bad for starters. still not finding my old gasket set, i continued skulking around. next i re-found my old mock up engine block from a few years back (12A housings and irons held together by a handful of tension bolts) i pulled the block apart and looked inside and remembered that those housings were my good pair aquired from several 12A tear downs, with virtually no flaking to speak of :O. it seems that im on a roll so far, why stop there? i continue digging around, completely forgetting about my original intentions, and my eyes grew wide as i saw 3 large flat boxes sitting next to some old irons. i opened them up and they contained what i thought
a set of irons i bought years ago, and "R5" front, and "Y" intermediate and rear irons that were Mazda Factory refurbished and renitrided...essentially brand new in the eyes of Mazda.... ---back story--- apparently a while back, after mazda already discontinued the production of pre-86 irons, they still needed a supply for factory reman'd motors that were requested here and there. mazda did the only thing they could at the time, which was buying back old 12A's from salvage yards, dismanteling them, and refurbishing the irons. mazda spec'd them, resurfaced them and then re-nitrided them and either built reman engines or sold off left over stock. luckily i found a full set (tho not matched for production/casting runs) Lastly, a few feet away i also saw a pair of S3 12A rotors, counterweights and E-shaft.so now in my hands i (re)have...
Weber 50 DCO/SP w/ manifold/pump and regulator
a pair of excellent 12A housings
Factory "new" 12A irons
and a full S3 rotating assembly
this engine wont be an immediate build, but will be done over the next several months as i aquire seals and parts under the radar of.... the wife
im leaning heavily towards a full bridgey regardless of the route i take, and im also leaning towards using some ALS 1 piece ceramic seals... that being said, this is where my build ideas are branching of in 2 different directions and would like some input/suggestions
1) should i build a pure 12A bridgey?
or...
2) I have a friend who works at a machine shop and im considering having him mill a set of either 13B turbo FC housings i have, or some FD housings to accept coolant o-rings for use on pre-86 irons, and picking up a S5 NA rotating assembly, and ultimately building a nasty 13B bridgey
...and for the old school vets, what kinda meat do i have to work with for porting in the "Y" and "R5" irons? i think i remember reading a while back that the "R5" have more material to work with, but again, im not sure. any advice will be much apreciated
10-19-11, 10:48 PM
#2
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neat! i'd take door #1, and do a pure 12A bridge. the only twist is that i'd got for a wide short bridge, so it opens later than a normal bridge, and close at some sane time. think high lift short duration.
be fun!
be fun!
10-20-11, 10:19 PM
#3
sounds interesting 
well, today for my own curiosity. i picked up some 5/8" dowels, 5/8" drill bit and a few sheets of plexiglass so i can map out seal paths and make my own porting template. tomorrow im gonna grab some old stat gears and an e-shaft. ill use the eshaft rotation to give me an accurate idea of side seal and corner seal tracks.
also, on a side note, due to cost limitations of this being a secret "budget" build i have decided to run carbon seals, as opposed to ceramics
well, today for my own curiosity. i picked up some 5/8" dowels, 5/8" drill bit and a few sheets of plexiglass so i can map out seal paths and make my own porting template. tomorrow im gonna grab some old stat gears and an e-shaft. ill use the eshaft rotation to give me an accurate idea of side seal and corner seal tracks.also, on a side note, due to cost limitations of this being a secret "budget" build i have decided to run carbon seals, as opposed to ceramics
10-22-11, 08:33 PM
#4
spent most of my day today mapping out seal paths and making my porting template out of some plexiglass, making sure the bridge is supporting enough corner seal and the leading edge of the sideseals. the old 1st gen irons seem to have a lot of meat around the bowls of the port, this one is gonna be fun 
here is the current scribing for intake ports, porting will start tomorrow
here is the current scribing for intake ports, porting will start tomorrow
10-22-11, 09:34 PM
#5
i did seem to find an issue with the housings i posted this quote in old school section to widen my chances of finding the answer. jeff20b, trochoid, J9fd3s im looking at u guys. the key here, in case its overlooked at the bottom, is the sparkplug holes depth
i posted this quote in old school section to widen my chances of finding the answer. jeff20b, trochoid, J9fd3s im looking at u guys. the key here, in case its overlooked at the bottom, is the sparkplug holes depthim putting this question in the old school section because i think i may have a pre-rx-7 12A housing and i need some info. im starting another build due to recently re-finding a plethora of parts that i have accumulated over the years and forgot about.
the problem is this... i have 2 12A housings that have excellant chrome with almost imeasurable flaking. these 2 housings i have have some obvious, and not so obvious differences that may make them non-compatible with eachother.
here is a comparison pic.
obvious difference
1. raised vs contoured area around where "12A mazda" is cast
2. smooth vs ribbed outer "shell" of the housing
3. raised boss vs smoth area around sparkplug hole
4. square block vs. "H" shaped casting on the top of the housing
they both have the same spark plug location and same stock port timing on the exhaust, but the only difference im concerned about is the depth of the sparkplug holes. i saw what could have been an anomoly today, when i was spec-ing them out, around the spark plug area so i measured the depth of the spark plug seat to the inside surface or the housing and they were almost .2" different. so then to 100% confirm this, i ran a pair of NGK BUR8 sparkplugs into them and for sure, 1 is just shy of the combustion chamber surface while the other is abt 1/4" sunk in.
does anybody know which housing if from what generation 12A?
...and can i use these housings together in the same motor, as long as i use the sparkplug for whichever generation each housing is?
the problem is this... i have 2 12A housings that have excellant chrome with almost imeasurable flaking. these 2 housings i have have some obvious, and not so obvious differences that may make them non-compatible with eachother.
here is a comparison pic.
obvious difference
1. raised vs contoured area around where "12A mazda" is cast
2. smooth vs ribbed outer "shell" of the housing
3. raised boss vs smoth area around sparkplug hole
4. square block vs. "H" shaped casting on the top of the housing
they both have the same spark plug location and same stock port timing on the exhaust, but the only difference im concerned about is the depth of the sparkplug holes. i saw what could have been an anomoly today, when i was spec-ing them out, around the spark plug area so i measured the depth of the spark plug seat to the inside surface or the housing and they were almost .2" different. so then to 100% confirm this, i ran a pair of NGK BUR8 sparkplugs into them and for sure, 1 is just shy of the combustion chamber surface while the other is abt 1/4" sunk in.
does anybody know which housing if from what generation 12A?
...and can i use these housings together in the same motor, as long as i use the sparkplug for whichever generation each housing is?
10-22-11, 09:50 PM
#6
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which one put the plug closer?
the housing with the H on it is an 81-85 housing, and the other one is a 78-80 housing.
the housing with the H on it is an 81-85 housing, and the other one is a 78-80 housing.
10-22-11, 10:01 PM
#7
im not 100%, i forgot to take note which one it was, but i want to say it was the later housing, the one with the boss' cast around the sparkplug hole that allowed the plug to sit closer. i thought all 1st gens used the BR8-EQ's, did mazda change things secrety over the years (which they have been known for doing) or did the early/pre SA's require different plugs?
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10-22-11, 10:35 PM
#8
The 79 12a uses BR7ET plugs, I have always thought the reason mazda added the raised eyebrow around the spark plug holes on the later housing was to prevent people from installing the wrong splark plug, as installing the BR7ET plug on a later housing results in the sparkplug nut sitting under the raised eyebrow and not allowing the sparkplug socket to reach the nut. This is why mazdatrix and racing beat sell a thin wall spark plug socket so one can install short body plugs on later housings.
10-22-11, 11:08 PM
#9
just did some digging around at the ngk site, S1 motors used the BR_ ET, S2 and S3 used BR_EQ, but both plugs have the same 19mm reach. the only difference in spec was the EQ's have 4 electrodes instead of 3 and the gap is 1.25mm instead of 1.05mm. it seems that mazdas earlier design kept the sparkplug tip more recessed than later. it seems that im gonna have to do a lot of homework now to find a pair of sparkplugs that have the same specs, asides from reach i will probably have to do what paul yaw did in his earlier spark plug experiments and spend hours looking through old sparkplug books to find applicable plugs and testing them while my housings are sitting out. i remember reading that mazda did the added casting around the plug holes to prevent people from experimenting, using plugs that had a 15/16" head, or a shorter or longer body. i suppose i will take care of that added material with my diegrinder too when im porting the exhaust
im not worried about the trailing plugs, which seem to have the same depth, as im will be running a leading only ignition using a spare MSD to fire a FC leading coil as a direct fire
i will probably have to do what paul yaw did in his earlier spark plug experiments and spend hours looking through old sparkplug books to find applicable plugs and testing them while my housings are sitting out. i remember reading that mazda did the added casting around the plug holes to prevent people from experimenting, using plugs that had a 15/16" head, or a shorter or longer body. i suppose i will take care of that added material with my diegrinder too when im porting the exhaust im not worried about the trailing plugs, which seem to have the same depth, as im will be running a leading only ignition using a spare MSD to fire a FC leading coil as a direct fire
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