Druken

So my setup is a 79' tranny on a 91 n/a block. I read that the 12a trannies can only take up to 160(?)psi before they break, so will I come across a problem with my motor? When I did the equation to figure out the amount of torque the engine should produce, it seemed like it would produce more at lower rpm's, so I'm confused.

Torque = (hp x 5252)/RPM

right?

If there is going to be a problem, what rpm range should I avoid before I do a tranny swap?

SIXSERIESCSI

Hmm, I am have no potential information relating to this issue, But I too have heard that the Mazda 12A Transmission is not the strongest. I've heard people talk about mounting a Ford Transmission, but not to sure, I belive there is a Bracket you can buy that will mount it right up. Ask around though. I am just curious to know the amount of Torque that a stock Transmission can take.

DriftFB

I hope you're not measuring torque in psi. But the 13B trannies will bolt right up, if you search you'll find some very helpful threads on it.

And if your starting a reply with "I have no information to this issue," why do you chime in?

Jeff20B

iTrader: (13)

The '79 tranny I installed in my REPU didn't live long. It had high miles though. The '81-'83 tranny I installed in an RX-4 is still going strong (even with a supercharger). It had low miles.

Druken

Okay, I guess I'll drive her softly when I get her on the road, while looking for a T2 tranny.

Yeah I know the 13b tranny will bolt up, but I don't have much money flowing in anymore so I wanted an estimate on the lifespand of the 12a with the setup. It lets me plan before hand and I'll keep searching since it seems like I missed something.

13BT_RX3

The 12a trans is pretty tough.

I had a 13B J-Bridge in my '83 RX7 with stock trans for ~8 years. Tranny held up fine and the car was beat well too. 4.625 rear gears made second gear burnouts to 60mph a common trick. Tires were 205/60-13 A008Rs. The only things that went bad after much abuse were the second gear syncros(common problem), a U-joint(once) and axle splines got loose(axles and diff splines deformed). I did have an Aluminum flywheel though.

I have not head any good things about the 2nd gen NA trannies though.

DriftFB

Yeah, the TII tranny is what I was refferring to, if its good enough for factory 200 hp its good enough for my 12A.

trochoid

iTrader: (6)

Torque relates directly to rate of acceeration. The slower you accelerate, less hp is used, thus less torque.

13BT_RX3

A TII tranny is good. The gear ratios alone are worth changing for. Especially with the 2nd-3rd and 4th-5th splits. I have one for my RX3. Breaking a trans with too much torque isn't cool. I blew third off the T5 in mustang. That sucked!! I am glad the little gear bits didn't lock the trans up.

Druken

Thanks for the info, I'll be keeping an eye out for a TII tranny.

coldy13

With the TII tranny you'll have to get a new clutch and make a new mount. The 12a tranny should have no problem holding an n/a unless it's a bridgeport or if you're using an unsprung puck clutch. I've been using the 12a tranny with 170rwhp and 180tq on my 12aTurbo with a 6puck sprung hub clutch for a few years and have only broken one, but that one REALLY broke. I shifted into 2nd gear at full boost and my tires actually hooked instead of burning out like normal, I heard a loud crack, and lots of metal pieces flying around inside the case. I didn't pull the case apart, but I'm assuming it's now a multiple piece countershaft since it lost 1st, 2nd, 3rd, 5th, and reverse.

13BT_RX3

Did you miss my post? I had a J-Bridge 13B with a 12A trans for 8 years and it didn't break.

coldy13

Yeah, I usually just read the first post and respond to it. I didn't think a 12a tranny would be able to take the higher revs and the higher power at those RPM's of a bridgeport, or at least it'd start to have problems shifting after a while, but 8 years without it breaking it.....that's a lot longer that mine lasted on a stockport 12a turbo.

13BT_RX3

Torque is usually the problem. How much torque do you have? That would let people know how much the 12A trans can take.

When I blew the T5 it was pretty much at the torque peak after a smooth roll on (302 with 11psi).

coldy13

170rwhp 180tq on an eddie watt dyno, over 200 on an inertia wheel type. I shifted into 2nd and broke every gear but 4th. That was the original tranny in my car with 135k on it before adding turbo, lasted 3 years with the turbo.

13BT_RX3

Looks like Mazda had a saftey factor of ~2. Since you have about twice the torque of a stock 12A.

85rotarypower

People don't give the 12A trans enough credit, including me. Seeing the info here has changed my mind a little to the strength of the 12A trans. I'm running a S4 13B with many mods including a HD clutch and lightweight flywheel. I'm really hoping the 12A trans and rear end will hold the power. I have a feeling the rear end will let go first. 275K KM can't be good for its strength, and the LSD is already gone. Guess I'll have to stock a spare 82 LSD pumpkin.

I don't belive that torque equation properly applies to fossil fuel engines. There is WAY too many variables that determine the torque an engine will make.

coldy13

The stock rear end is stronger than the stock tranny, so unless it's having problems other than the LSD it should hold up fine. That torque equation is only for if you know the HP and at what RPM of the engine. It's how a dyno figures out HP, it measures torque and RPM and calculates HP from it.

Druken

When you guys broke your tranny, how high were your rev's? Because from the sound of it, you guys seem to push your 7's. Its not that I don't or won't but I dont want to be stuck in the situation where I'm stranded on the highway somewhere.

So right now I have the 91 n.a. block with the s5 pp/flywheel and a brand new 6 pluck clutch with a 79' 122k miles tranny... how long do you think I would be able to last if I didnt rev to redline but close, 5.5-7k rpm.

coldy13

It'll last a long time, an n/a doesn't have nearly as much torque as a turbo. I shift mine at 6500-7k since the turbo is too small and loses power after that. I have a ceramic 6puck sprung hub, stock flywheel and 205-60-13 sumitomo HTR200 tires. I think mine would have lasted a bit longer but the week before it broke I put on 20" diameter 13x7 Hoosier roadrace slicks and beat the sh*t out of my car.

13BT_RX3

I had a 13B J-Bridge and reved to 10,500 for 8 years and no problems except second gear syncros. Torque at wheel probably only 130ft-lbs or so. Turbos are what break S#!t. But it's for the same reasons that we like them... Torque.

LSD rearend are strong. Open diff rearends are very fragile!! My friend blew the one in his '84 with a stock 12A.

Druken

I just bought an 81 GSL rear (disk/lsd/etc) hopefully that will reduce the posibility of it breaking, because I would like to keep the car as stock as I possibly can, besides the engine. From your posts, I'm getting excited and tempted to really rev it. Isnt that one of the main reasons why people like the rotary? For insanely high revs?
As for turbos, I'm not headed towards that direction so thats good for me. If anything I'm going to keep it as n/a or if I get a lot of money from somewhere, the sky possibly, Id go supercharged but thats a 1% chance.

85rotarypower

Most people don't like the rotary for the insanely high revs. Its all about the smooth power and torque curves the rotary can make. It doesn't tend to be as peaky as a piston engine and overall they just run smoother. For the size and weight, they also make real good power if done right. My S4 NA engine has solid engine mounts and you can feel the engine vibrate more in my mom's brand new Dodge Neon with stock mounts and it makes more power too. Stock, the engine I have does 145hp or so. The way I have it set up, i figure about 170-180hp with probably 140 torque and a 7000rpm redline. Your S5 engine can go to 8000 max. Any more and you risk blowing up the clutch from too many RPMs.

13BT_RX3

Most stock rotarys can go 8000-9000RPM with no problems if they are being properly maintained. Bumping the oil pressure up a bit is good insurance though. The problem is that if the engine doesn't make power up there then there is no reason to rev up there. Airflow is the limiting factor. Porting, big intake and exhaust is the simple solution.

Rogue_Wulff

The SA (79-80) trans weren't quite as solid as the FB (81-85), but it should hold up pretty well. What will kill any trans faster, is sticky tires, and driving hard. Keeping good oil, and plenty of it, in the trans will go a long way towards extending it's service life. Avoiding 4K launches with racing slicks also helps.
The N/A 2nd gen trans were basicly the same units as the 81-85 12A, with different gear ratios. Treated roughly, the N/A 13B could eat one up in about 10K miles. Without constant abuse, the same trans could easily last 150-200K, with proper oil change and level checks on a regular basis.