soslowgtp

I've tried searching but I can't find much on the 12a Turbo sold in japan. I am wanting to turbo my 85 gsl and am trying to decide whether I should rebuild my 12a and mod it or just buy a japanese 12a turbo that I can get for under 1500.

If I rebuild my 12a I would end up switching it over to EFI, maybe even electronic ignition. Any comments or suggestions would be appreciated.

Anthrax Mike

Does the imported 12a come with wiring harness and ecu?

soslowgtp

I know it has the wiring harness, but I'm not sure about ECU

perfect_circle

is it that important to you to have a jspec 12a turbo? cause uyou could build a turbo kit for less than 1500..

Anthrax Mike

Well put down another grand + for a stand alone fuel system to compliment the engine. But I still think it'll be better than stripping down your current 12a and building it up. Finding a turbo, custom manifold and the like. Its more straight foreward. The 12at comes with a lower compression rotor, and from what I've heard is internally a bit more ready to handle the power. As long as the motor was in good/ready-to-drop-in-on-screwing-around-with-it-working order, I'd go with it.

And plus it'll make people jealous because its a factory 12at. Rather than a pieced together pile of parts.

I think that theres something to be said about that.

soslowgtp

It's not really important to me, but it will cost less than rebuilding, adding a turbo, EFI, and tuning my 12a. The 12at only has about 44k miles on it, while mine has about 130k. I know they last longer than 130k but I wouldn't feel right adding a turbo w/o rebuilding just to make sure.

soslowgtp

I have about $3000-$3500 to spend on everything, What do you think would be a reasonable goal hp wise ?

FB II

oh really... what's to be said about that? hmmm that you took the easy way out? hell, to me it sounds like someone didn't want to put any effort in the project. you gotta remember, these OFFICIAL something to be said about 12aT's have been just sitting in junkyards. PLUS... if you even CAN find one it's going to cost the same if not MORE than a TII motor. AAAANNNND... even if it does only have 44k miles... it's whole life was boosted and who knows how well it was taken care of. the main advantage of the 12aT motor is NOT the lower compression rotors, it's the larger exhaust ports so it flows a little better. for the same money you could rebuild your current 12a and just open up the exhaust ports and you'll make more power.

you will end up piecing together a setup on the 12aT anyways when you get sick of the stock turbo that's about the size of my thumb. it's "something to be said about" manifold doesn't have the foot print to rock out a nice turbo or even a TII turbo. the motor most likely does not come with a full harness and most definitely not the ecu. you can carb it with a stock nikki that will fit right on the stock 12aT intake manifold..... but to me that just sounds like you should have just gone with your original 12a and made more power.

sorry, i just took a little offense to what you said because from the response i have recieved... there's actually something to be said about making something work that was never intended to be setup like that. it feels good and it's faaaast.

j9fd3s

iTrader: (3)

anyone have pics of the 12at intake? maybe taken apart?

Anthrax Mike

No offense taken.

And its not that I don't want to drop time/effort into a project. I'm in the middle of just that. But everyone is not me.

And not everyone has the experience to just jump into something. I know it feels good to piece everything together one's self. But I've been trying to do just that for going on two years almost, due to the lack of fund-age, and everytime I get beat off the line by a car that daddy bought I clutch my steering wheel and grit my teeth wishing my turbo was done.

sigh

Anthrax Mike

I have mine dismantled but its at home and I have no pics, feel free to ask a question though, I'll try to help.

PaulFitzwarryne

Changing from 12A to 12AT is not just a case of dropping in an engine. You need to upgrade to a high pressure fuel system, add a BOV, install a FMIC and FMOC, buy a ecu, upgrade the exhaust/muffler. If you are serious then upgraded clutch and flywheel. The stock turbo, TO3 equivalent, is good for 200rwhp in a street car. FB must have big hands if its the size of his thumb! If you are want more than 200 for straight line power, than you will need to get a larger turbo. For that you will need to get a good fuel/ignition ecu.

The cost of the engine will be less than one third of the total cost. of the project. That is without upgrading the suspension and brakes to cope with the additional power!

Most likely the engine came from a Cosmo with auto transmission and was never thrashed. They tended to be a status symbol and just driven slowly at weekends. I would still pull the engine apart before you install, and as a minimum respring. At 6psi max the adverse effect on seals will have been limited.

As FBII said an early 13BT engine would be cheaper, it would be marginally heavier but some 10% more powerful in an identical configuration. If you have the money go for 13BT, if on a budget go 12A with a carb and rebuild when you can. If you want a genuine Gen 1 and have the money go 12AT.

soslowgtp

Llike I said I have about $3500 for just the engine and stuff right now, and I don't want a 13b. over the next year or 2 I'd like to reach 250-300whp for less than another $3500. What I really need to know it which one will give me the best results and if that is a realistic goal.

I'm new to rotaries, but I know that a lower compression ratio in piston engines can make a huge difference in the amount of boost and power you can make. why doesn't it seem to matter with a rotary engine ?

j9fd3s

iTrader: (3)

whats the intake manifold like? is it like a 12a carby intake? how does the 3 barrel tb go into that?

FB II

it does matter, but not directly to power. think of it as more "room for error" in a sense. there are many people running very high compression and upwards of 25 - 30 psi. and easily 16- 20 on pump gas. everyone has their opinions on low and high compression rotors but just because you have lower compression rotors will not equal more boost/ power. it's all in the tuning. you could have the 8.5:1 s4 TII rotors and blow your motor at 5psi. to me anything under 10:1 is safe

boyee

iTrader: (3)

you dont necessisarily have to add a bov am i correct?

to soslowgtp... fyi there is a 83 jdm stock 12aT selling (for a few months now) on ebay: http://cgi.ebay.com/ebaymotors/1983-...QQcmdZViewItem
not sure if it runs, has ecu, harnesses, etc. the price is kinda high too.. imo.

soslowgtp

Thanks, but I know where I can get a low milage 12at engine w/ wiring harness for under 1500.... no ecu but one of my friends that likes rx-7's lives in japan so he might be able to find me one, or I could just do a standalone efi system.

soslowgtp

I have a Grand Prix GTP, I have a turbo kit for it, the same turbo kit is made for GT's but since a GTP has lower compression I got an upgraded turbo and put down just over 100whp more than one of my friends who has one on his GT.... That is why I was asking, we have the same parts, except I have a bigger turbo running more boost, same shop did the tuning but I got about 30whp more gain out of it than him. I just wanted to know if the same was true w/ 12a vs 12at.... but I'm not sure what the compression ratios are or how much of a difference it'll make since so many people with turbo rx-7 say it doesn't make much of a difference

Anthrax Mike

The intake is a four port, and it has the horizontal air injection port beneath the two center ports. The throttle body has its three "barrels" set up in a triangle arrangment, but their bunched closely together. There are two smaller barrels sitting in-line with each other, and one larger barrel which forms the peak of the triangle. The two smaller barrels feed the far left and right ports, while the larger center on splits off into the two center ports. Also there are a total of four throttle plates between the two smaller barrels, it almost appears as though it might be used as a choke effect or perhaps its made to swirl the air because the to injectors are positioned at the end of ports, though not on the intake itself. The larger barrel has only on throttle plate.

Sorry for high-jacking.

soslowgtp

ok, so after a little research it looks like the compression ratios for 12a vs 12at are 9.4 to 8.5 ... that would be the same as a GT vs my GTP.... ???? So now I'm lost as to how compression ratio is still important if so many people say you can tune it for the same power ???

FB II

again. it's all in the tuning. in theory if you took two identical engine setups and dyno'd them, but the only difference was one had lower compression.. at the same PSI the lower comp motor will generally make less power. but the egt's may be lower and the like. from what i have seen people with the jdm 12aT make around 180rwhp at 10psi on tII turbos. people with usdm 12a's generally make 190 - 220 at 10psi on the same TII turbo. with mine i have pulled on cars trapping 110mph in the 1/4 on the highway. i'd say i atleast have 200rwhp and that was at 10psi on a halfway blown motor. now the car is insane at even 6psi with perfect compression on all faces. still have the stock high compression and will never look back.

plus off boost drivability is nice

Anthrax Mike

Just basically, compression makes power, the more you squeeze a air fuel charge the more power when it ignites. The problem is that when you squeeze the charge you also heat up the charge, and if it gets so hot it may predetonate and "ping" before the ignition system has a chance to do its thing.

Just think of it as it being a controlled burn at the right time when your spark plug does it. But when it detonates its uncontrolled and at the wrong time, there is the pontential you can have two flame front colliding with each other which makes an audible "pinging" noise.

This can be overcome be retarding ignition timing or a higher octane gas.

So when you turbo charge an engine your actually compressing the air charge a little bit. And as before this heats up the air alittle. So now it enters the engine where it becomes compressed again, this even further heats up the charge increasing the chance of "ping" at certain conditions.

Typically the leaner/more advanced timing causes this.

So the idea is to put a lower compression piston/rotor into the engine to lower the amount of squeeze that takes place and therefore heat. I don't know why I wrote all of this now that I look at your question. But anyway, the point is that if you have two engines, in this case having a compression ratio of 9.4 and 8.5 with the same boost numbers the 9.4 may make more power but runs the higher chance of pinging under load, while the 8.5 may make less power but be safe to run a greater advance at any given rpm, which if I remember right also makes more power.

Also in theory you can run a higher boost at for the 8.5 over the 9.4 due to its lower ratio. And this will increase volumetric efficency, the amount of air in the engine vs. the amount it can actually hold. Which will make for increased power.

But then you can intercool and run a little rich which cools combustion temps, so I think its complicated. I actually feel more confused.

Though I'm going to try and use my 8.5 rotors when I build my engine, because I can't afford to have it go >poof<.

Anthrax Mike

good point.

Power band is just as important, as peak power.

I thought the 12at J-spec made like 170 stock, what psi where they running?

FB II

i believe the jspec 12aT made 130 to the wheels. that's no more than 150 - 160 flywheel stock. base boost pressure is 6psi i believe.

what you explained about the compression differences is correct. that's exactly what i was saying.... it's all in the TUNING. "lower compression gives more room for error"

that's how it works. in any case, you need to tune for safe air/fuels and egt's. if you keep these down on any motor you will get the most out of it when turning the boost up. each tuner has his own target points with timing and the like and some have their preferences in high or lower compression.

all i know is i've hit 20psi with no detonation or "pinging" of any sorts. just breakin the tires loose in 5th gear this was with my afr's in the low 11's and timing at 10degrees locked where i leave it. the guy that built my turbo header runs locked distributors... high compression... and upwards of 30psi!!! hahahhaa and he's hitting 9's in the 1/4. fast *** rx3 i wish he would get in on this with his thoughts of compression.

Anthrax Mike

I always wonder what fuel their running. Sometimes I think people see these numbers and figure its attainable not knowing much else about it. But its damn impressive none the less.

Yeah, all my rambling is from what I've learned/heard. Its not quite so practical, so it would be nice to hear from someone who is running serious boost.