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what is diff between 12A & 13B?

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Old 10-21-03, 08:17 PM
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what is diff between 12A & 13B?

I am a brand new (used mazda RX-7 owner. What is the difference between a 12A and 13B engine? I have a 1984 RX-7 with a carburator. What do I have?
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Old 10-21-03, 08:30 PM
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probably 12a but could be 13b...look on the block and you'll see...
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Old 10-21-03, 08:32 PM
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You have a 12A. The difference is the size. The 13B has wider rotors for the most part. I believe that some of the other specs for the exact dimensions on the internals are a little different also. The main thing is wider rotors=larger dispacement. Try this link it will explain it.



https://www.rx7club.com/showthread.p...e+size+12a+13b

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Old 10-21-03, 08:32 PM
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You have a 12a. The difference between a 12a and a 13b is the size. The 12a was a 1.1 liter, and the 13b was a 1.3 liter. In addition the 13b only came came on the GSL-SE, and was fuel injected.
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Old 10-21-03, 09:25 PM
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slathey, i noticed you are from central ohio. you coming to the meet? if you havent seen anything go to the north east seciton of the forum and go to the last meet of the season thread. what color is your car. i have seen a few new 1st gens around columbus lately.
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Old 10-22-03, 12:48 AM
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what's the difference? About 30-35 hp.
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Old 10-22-03, 01:04 AM
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Some people carb their FI 13b's. The easiest way to know for sure is to look on the block by ur oil filler neck. Should say Mazda 13b or Mazda 12a.
Biggest Differences:
13b:
1.3 L
Fuel Injected
135 hp 133lbs of torque
Came on 84 and 85 GSL-SE's
12a:
1.1 L
Carbuerated
app. 115ish hp and 100ish lbs of torque (i don't know much about the 12a's)
Hope this helps. More than likely you have a 12a.

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Old 10-22-03, 02:59 PM
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Some notes on the SA22/FB 12A and 13B differences;

The 13B engine was featured by Mazda in the 84/85 GSL-SE's with some innovations of intake design, namely, the Dynamic Effect Intake system which used the pulse of the airflow through the throttle body and the intake plenums to 'force' the air column into one intake port vs. the next. This is one of the reasons why the 13B engine developed not only more horsepower (135 stock), but also more torque at a lower range than the 12A carb'ed engines.

Since air has mass, and operates like a fluid, the Dynamic Effect Intake used this air mass to 'pack' more air into the engine at all engine speeds, but when combined with the '6'-port induction, this gave significant performance improvement. The '6'-ports are rotary valve sleeves that open only under heavy exhaust backpressure (i.e., high power output conditions) which allow for more air to enter into the combustion chambers for more power. The '6'-ports are the rotary equivalent of Variable Valve Timing in today's piston engines, and provided for better power at low RPM - a shortcoming of the rotary engine.

Additionally, the 13B engine made use of 3mm cast iron apex seals at the rotor tips, which provide both added reliability and good sealing throughout the life of the engine. The 13B rotor housings were wider than the 12A version, and displaced 1308cc's compared to the 12A's 1176cc's - this alone accounts for more power produced.

The 13B RE-EGI (Rotary Engine - Electronic Gasoline Injection) in the GSL-SE models available in 84 and 85, only, utilized 2 fuel injectors of 680cc flow (nominal at 60psi fuel pressure), and were mounted to the engine center housing - this was later changed in 2nd Gen cars to house the injectors in the intake manifold and runners. These 2 injectors provide fuel as determined by need via an Airflow Meter mounted behind the left headlight.

The 13B engine, in it's 6-port designation, was a specific improvement on the previous 4-port 13B engines used in prior rotary cars imported to the US and elsewhere. Overall, the engine design, while only slightly different in core build, generates much more power and driveability than the 12A powerplant - primarily due to better engineering and gradual improvement of the engine over the life of the 1st Generation cars. HTH,
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Old 10-22-03, 07:35 PM
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Originally posted by Rotor13B
what's the difference? About 30-35 hp.
The 12A can make as much power as the 13B. Both engines are limited by the size of the ports, the 12A just has to rev higher to make the same power.

So the real answer is... about 20mm.
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Old 10-22-03, 09:25 PM
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Originally posted by peejay
The 12A can make as much power as the 13B. Both engines are limited by the size of the ports, the 12A just has to rev higher to make the same power.
when modded, mostly true. In stock form however the above 30-35 hp post is correct.

The 13B also benifits from a bit more torque, coming on early and staying until the party really starts.
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Old 10-22-03, 09:59 PM
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The 13B will always have more torque. It has more displacement, displacement = torque.

If you're going to do engine work, it's easier to modify the 12A than it is to swap in a 13B. (Not that it's hard to swap a 13B, it's just that much easier to modify the 12A) If you're not going to do engine work... then it doesn't matter what you have, now does it?
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Old 06-20-15, 06:01 PM
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Well I'm getting back my 12A 1979 that I gave to a friend a few years ago. He dropped in a 13B 4 barrel holly into it. Now 325 hp!!! We will see!
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Old 06-28-15, 03:21 AM
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13 b

Originally Posted by LongDuck View Post
Some notes on the SA22/FB 12A and 13B differences;

The 13B engine was featured by Mazda in the 84/85 GSL-SE's with some innovations of intake design, namely, the Dynamic Effect Intake system which used the pulse of the airflow through the throttle body and the intake plenums to 'force' the air column into one intake port vs. the next. This is one of the reasons why the 13B engine developed not only more horsepower (135 stock), but also more torque at a lower range than the 12A carb'ed engines.

Since air has mass, and operates like a fluid, the Dynamic Effect Intake used this air mass to 'pack' more air into the engine at all engine speeds, but when combined with the '6'-port induction, this gave significant performance improvement. The '6'-ports are rotary valve sleeves that open only under heavy exhaust backpressure (i.e., high power output conditions) which allow for more air to enter into the combustion chambers for more power. The '6'-ports are the rotary equivalent of Variable Valve Timing in today's piston engines, and provided for better power at low RPM - a shortcoming of the rotary engine.

Additionally, the 13B engine made use of 3mm cast iron apex seals at the rotor tips, which provide both added reliability and good sealing throughout the life of the engine. The 13B rotor housings were wider than the 12A version, and displaced 1308cc's compared to the 12A's 1176cc's - this alone accounts for more power produced.

The 13B RE-EGI (Rotary Engine - Electronic Gasoline Injection) in the GSL-SE models available in 84 and 85, only, utilized 2 fuel injectors of 680cc flow (nominal at 60psi fuel pressure), and were mounted to the engine center housing - this was later changed in 2nd Gen cars to house the injectors in the intake manifold and runners. These 2 injectors provide fuel as determined by need via an Airflow Meter mounted behind the left headlight.

The 13B engine, in it's 6-port designation, was a specific improvement on the previous 4-port 13B engines used in prior rotary cars imported to the US and elsewhere. Overall, the engine design, while only slightly different in core build, generates much more power and driveability than the 12A powerplant - primarily due to better engineering and gradual improvement of the engine over the life of the 1st Generation cars. HTH,
thanks, that is some good info,
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Old 06-28-15, 08:16 AM
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Originally Posted by slathey View Post
I am a brand new (used mazda RX-7 owner. What is the difference between a 12A and 13B engine?
20mm.
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Old 06-28-15, 08:17 AM
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Originally Posted by peejay View Post
So the real answer is... about 20mm.
Wow, I didn't realize this was a 12 year old post.

But good to see that I'm still the same dick I've always been, 12 years later
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