1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

jdm 12a turbo

Old 07-03-04, 03:22 PM
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jdm 12a turbo

i was wondering if anybody in this forum has owned and/or have done performance mods to the actual 12a turbo motor from japan.I'm curious on what the max power is for these little motors could be, safely. Im thinking about getting hardened stat. gears w/ 3-window bearing, "cryo"ing my e-shaft, sideplates & housings, carbon seals, mild bridge port/or j-bridge port and a new turbo( a mild tII upgrade).what do u guys think, decent setup?any ideas of the power flywheel)?
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Old 07-03-04, 03:37 PM
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IIRC the main diffenece is the stock ports are smaller, its EFI, and lower compression
robert gets 720hp so the sky is the limit almost, mostly a question of relability
carbon seals supposedly suck for boost and wont last at all
and you should ad dowelpinning to your list
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Old 07-03-04, 03:43 PM
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The 12at is efi? really? I always pictured it as a blowthrough.
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Old 07-03-04, 03:44 PM
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Originally posted by Tanjo
The 12at is efi? really? I always pictured it as a blowthrough.
yea, similar to the SE 13b setup IIRC but 4 huge *** injectors rather than the gsl-se's 2
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Old 07-03-04, 03:48 PM
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Damn. I got a buddy in the Merchant Marines, and ehs lways asking if I want something from Japan. i think Im gonna ask him to do a little junkyarding fo me, and find a setup for my car.
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Old 07-03-04, 06:53 PM
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thats exactly what i wanted to hear "the sky is the limit". hell if someone can get 720 hp, ide be happy with 300. btw what seals would you guys recommend? ceramic or hardened steel?
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Old 07-03-04, 07:28 PM
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Ceramic.

Zac
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Old 07-03-04, 07:35 PM
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^overkill unless you want to push a ton of power. Stock seals are fine.

Marques
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Old 07-03-04, 08:59 PM
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The factroy 12AT runs (2) 800cc injectors on a very primitive Bocsh mass air EFI system.It doesnt even have a knock sensor,just a distributor with retard built in to activate during knock prone conditions.The turbo is very small and theres no intercooling.
The advantages are that it is a factory turbo engine,so the additional strength is there, plus lower compression.If you pitch the stock turbo and EFI you could hit 300hp with the ports only slightly opened up.Usually a bridge or J port isnt needed on a turbo engine,even the fastest forced induction rotaries often only have a streetport.Plus the bridgies tend to last a much shorter time due to the close proximity of the port to the water jacket.Stock steel seals are quite tough,as are the Eshafts.Most turbo engines make their best power in the midrange,so super high RPM mods arent as neccesary as with N/A engines.Compare the FD and RX-8 redlines.Which one has more torque and which one revs higher?The engine with the flat torque curve will win every time.
In general,the 12AT like the 13BT is a good turbo platform to build on.Although the 12AT is down a good 25-40hp on the 13BTs from the factory. And like the 13BT,the stock EFI controls leave a lot to be desired.The stock 13BT EFI can be pushed to 300 and be boarderline safe.The 12AT is only 160HP stock,so getting it to 300 will most likely be out of reach with the stock ECU and controls.
Plus you have to consider parts availibility.There are a lot more 13BTs around than 12ATs.
Just some info for you to digest.........
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Old 07-03-04, 09:31 PM
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the main reasons i want the 12a turbo motor was to basically make my own japo' gtx ( a 79' not 83'+), plus i dont believe that there are any modifications needed to drop that motor into a car with the 12a originally.the motor im planning on buying doesn't have the complete ecu/harness. so i was planning on getting a stand alone fuel computer any way, possably a megasquirt or haltech f9 flying lead kit. maybe even eventually getting an "IDA" style throttle body, manifold & turbo plenum and sourcing my own sensors and injectors.
oh and most engine prices ive seen are actually lower for the 12at than the 13bt despite that they are much less common
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Old 07-03-04, 10:30 PM
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Thats a cool idea.Ive never seen an original FB turbo in the states before.Itd be interesting to replicate one with a US chassis.
If your gonna pitch the stock EFI,then youve solved half the HP problem.The tiny stock turbo and lack of IC is the other half.Most of the internal improvements of the TII engines were pioneered on the 12AT engine,so itd make a good build up block.
12ATs are probably cheaper because of the low demand, compared to the 13BT.
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Old 07-03-04, 10:49 PM
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i forgot to mention that the first mods in the line up are a nice fatty intercooler and replacing the hitachi POS baby turbo with T04B or E, TD06SH-20G or a garrett GT turbo set up and limit it to 6 PSI o' boost at first
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Old 07-04-04, 06:23 AM
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Originally posted by steve84GS TII
The factroy 12AT runs (2) 800cc injectors on a very primitive Bocsh mass air EFI system.It doesnt even have a knock sensor,just a distributor with retard built in to activate during knock prone conditions.The turbo is very small and theres no intercooling.
The advantages are that it is a factory turbo engine,so the additional strength is there, plus lower compression.If you pitch the stock turbo and EFI you could hit 300hp with the ports only slightly opened up.Usually a bridge or J port isnt needed on a turbo engine,even the fastest forced induction rotaries often only have a streetport.Plus the bridgies tend to last a much shorter time due to the close proximity of the port to the water jacket.Stock steel seals are quite tough,as are the Eshafts.Most turbo engines make their best power in the midrange,so super high RPM mods arent as neccesary as with N/A engines.Compare the FD and RX-8 redlines.Which one has more torque and which one revs higher?The engine with the flat torque curve will win every time.
In general,the 12AT like the 13BT is a good turbo platform to build on.Although the 12AT is down a good 25-40hp on the 13BTs from the factory. And like the 13BT,the stock EFI controls leave a lot to be desired.The stock 13BT EFI can be pushed to 300 and be boarderline safe.The 12AT is only 160HP stock,so getting it to 300 will most likely be out of reach with the stock ECU and controls.
Plus you have to consider parts availibility.There are a lot more 13BTs around than 12ATs.
Just some info for you to digest.........
2 800cc vs 2 680, i knew it was somehting like that, thx
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Old 07-05-04, 06:43 PM
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The JDM 12AT is a junk engine, the ports are tiny with a turbo to match.

Do it properly and use the 12AT rotors in an 85 spec 12A engine and turbo it. Not sure if the US got 12As in later model RX7s, but Australia did. These are the pick of the 12A engines with much larger ports and the centre plates having the largest of all ports in the 12A series.

We have those engines over here making well over 400hp in street trim, with one in a 323 wagon recently running 10.8 on street tyres.
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Old 07-05-04, 06:48 PM
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don't quote me, but i think our '74-'78 12A engines had the choice ports ... either way, i agree with AJC13B screw the stocker 12A-T ... if you can get the rotors, then build your own custom 12A-T (with turbo, to boot )

****. use ported SE intermediates and go from there ...
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Old 07-05-04, 07:05 PM
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yea man, do what i did. just slap a turbo on a good 12a. i'm still using stock compression. eventually i will build up a 12a like ajc said. then i'll really be set. all i'm waiting on now is to make my own downpipe. then i'm ready to rock out!
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Old 07-06-04, 03:26 AM
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Not true Steve,

I still have the standard centre plate in my engine and am making decent hp.
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Old 07-06-04, 09:59 AM
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Originally posted by diabolical1
don't quote me, but i think our '74-'78 12A engines had the choice ports ... either way, i agree with AJC13B screw the stocker 12A-T ... if you can get the rotors, then build your own custom 12A-T (with turbo, to boot )

****. use ported SE intermediates and go from there ...
Originally posted by AJC13B
Do it properly and use the 12AT rotors in an 85 spec 12A engine and turbo it. Not sure if the US got 12As in later model RX7s, but Australia did. These are the pick of the 12A engines with much larger ports and the centre plates having the largest of all ports in the 12A series.
It'd be interesting to see the diffs betweenthe Aus/J spec and US spec engines year for year, to see which part would be best...

Mkae some kinda crazy hybrid engine outta x year housings, x year rotors, x year iron plates, etc etc...

Seems like the only thing you'd need off the 12AT engine is the exhaust manifold.
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Old 07-06-04, 10:33 AM
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i was wondering if anybody in this forum has owned and/or have done performance mods to the actual 12a turbo motor from japan
You said 'from Japan.' Are you talking about only cars that were sold over there, or would an American limited edition '79 still qualify?
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Old 07-07-04, 03:36 AM
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i actually meant any 12at motor/shortblock left realativily stock (stock housings and side/intermediate plates)with mostly bolt-ons and porting

Last edited by Sgt.Stinkfist; 07-07-04 at 03:44 AM.
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Old 07-07-04, 04:22 AM
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Originally posted by e1ement5k4ter
You said 'from Japan.' Are you talking about only cars that were sold over there, or would an American limited edition '79 still qualify?
12A Turbo was only available in Japan.
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Old 07-07-04, 11:37 PM
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Originally posted by AJC13B
The JDM 12AT is a junk engine, the ports are tiny with a turbo to match.
Do the stock port sizes matter if the motor is going to be ported?
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Old 07-30-06, 07:40 PM
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Originally Posted by Sgt.Stinkfist
Do the stock port sizes matter if the motor is going to be ported?
bump for answer
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Old 07-30-06, 09:50 PM
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Originally Posted by AJC13B
The JDM 12AT is a junk engine, the ports are tiny with a turbo to match.

Do it properly and use the 12AT rotors in an 85 spec 12A engine and turbo it. Not sure if the US got 12As in later model RX7s, but Australia did. These are the pick of the 12A engines with much larger ports and the centre plates having the largest of all ports in the 12A series.

We have those engines over here making well over 400hp in street trim, with one in a 323 wagon recently running 10.8 on street tyres.

this is true but the exhaust ports on the 12a turbo engines came with ports twice the size of any other engine sold anywhere and the rotor housings had oil injectors so the chrome lasted wayyyy longer too...
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Old 07-30-06, 09:58 PM
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Originally Posted by Sgt.Stinkfist
Do the stock port sizes matter if the motor is going to be ported?
the ports are alot smaller so labor to make the streetport will be alot more work = more money, thats it tho...
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