PulsE

Hey guys,

My friend has a first gen. When he was changing the oil when he saw "12 A Mazda". He was under the impression that it was either a 13A or 13B engine. I dont really know what to tell him so i was wondering if you could help me out.

Thanks

-PulsE-

Aesop Rock

only the GSL-SE had the 13b, if you don't have a 1985 GSL-SE, then your car has a 12A, and I have never heard of a 13A engine before

tempusfugitive

yeah.., there's no such thing as a 13a engine, it's either 12a or 13b

red_blast

If it says 12A on the engine, then... you've got yourself a 12A. His is more than likely carburated. The other possibility would be a 13B, but more than likely that would be fuel injected, unless its been modded.

--Lauren

Felgar

Aesop's right.

Plus, it's kinda hard to argue with the aluminum casting when it says 12A.

Another way to tell is stock 13B engines are fuel injected and stock 12A engines are carburated. So if you have a round blue air filter lid on top of the carb you can be 99% sure that it's a 12A.

RotoHead

12A motors aren't bad. Isn't the main difference between the 12A and the 13B in the rotor itself? Isn't that was accounts for the 1/10th of a Litre in displacement? At any rate, I could be wrong. I haven't even thought about a rotory in well over a year or so. But its so good to be back and reading again!

Felgar

Ya internally the main difference is certainly the rotor and the housing size. The intake is also different and of course the FI vs carb also.

RotoHead

Wow, there is a difference in housing size as well? I was under the impression that the rotors were the big difference. But, I really wanna get me a 20B so I guess it doesn't matter, eh?

Felgar

I've never had one apart but I couldn't imagine having more displacement without actually being overall bigger...

cosmicbang

There is a 13A engine, although not in the RX-7. The 13A was developed for the Mazda R130 (Luce Rotary Coupe), unveiled in October 1969 at the 15th Tokyo Motor Show.
http://www.mazda.com/history/rotary/n1-1.html

FirstGen7

If it says "12A" on the engine.............I'm gonna take a wild guess and say it's a 12A.

85rotarypower

Its deffinately a 12a. The luce was a low production, japanese only car. You can't even find the 13a anymore. Also, the GSL-SE was made in 84 and 85. Not just 85.

Elysian

100% correct... i'm kinda surprised more people don't know about the 13A... oh well who cares

RotoHead

I always thought the rotor was slightly smaller... allowing for 1/10th of a Litre more displacement.

Elysian

uhmm dudes... the rotors are 20mm thicker on the 13B than the 12A... the 13A had the same thickness rotors, but was the only mazda motor to use a different epitrochoid whatchamajigger

85rotarypower

NO! The rotors are 10 MM thicker on the 13B. It turns out to exactly 10 cu in of displacement difference. The 12A is 70 cu in and the 13B is 80 cu in.

cosmicbang

Actually the 13A had the same width rotors as the 10A. The 12A rotors are each 10mm wider than the 13A, and the 13B rotors are each 10mm wider than the 12A. In summary:
10A = 60mm
13A = 60mm
12A = 70mm
13B = 80mm

Not sure what you are disagreeing with, but you are not "exactly" correct. The rotor measurements are metric so it is not an "exact" nuimber in cubic inches:

12A = 2 rotors x 573 cubic centimetres (e=15mm R=105mm b=70mm) = 1146cc = 69.9332107 cubic inches
13B = 2 rotors x 654 cubic centimetres (e=15mm R=105mm b=80mm) = 1308cc = 79.8190573 cubic inches
13A = 2 rotors x 655 cubic centimetres (e=17.5mm R=120mm b=60mm) = 1310 cc = 79.9411048 cubic inches

The 13A has slightly more displacement than a 13B, but they are both "approximately" 80 cubic inches. AFAIK, there were 976 R130s built. They had front wheel drive and 13A engines. Very rare.

toyo_kogyo

Well said Not too many people know much about the R130. Its good to see some informative posts regarding it.

mazdaverx713b

iTrader: (91)

talk about bringing a thread back from the dead!!! good info in the thread though

trochoid

iTrader: (6)

The newbs are finally learning, I blame doc, lol. Some of the threads they've dug up recently I've never even read. Good find.

PaulFitzwarryne

Innocence!

There are engines with 12A on the casting which are not 12A engines!

First there are numerous 'fat 12As' which are in fact 13BTs. The reason is that in certain states in Australia you cannot drop a 13BT into an early Gen 1 because of weight limitations. Dropping a 13BT into late ones is sometimes acceptable with an engineering certificate. If you want a fast light car the technique is to get a light 79-80 model, grind off the 13B and replace it with a 12A casting mark! This way you get it through vehicle inspections.

Second there are 'long 12As', mainly in the UK. You can buy a three rotor engine built up from three 12A rotors and drop it into an RX-7 easier than a 20B. There were multi rotor engines built up for drag racers using the 12A castings. A four rotor might fit into a gen 1 with radical engineering. That would be fun to open up the bonnet at a show! I think the 3 rotor engines built in NZ like the one in 'Hitmans' car were also 12A based.

Regarding the 13A, Mazda built a series of experimental engines in the late 60s including the 13A, 15A, and 21A, with the intention of using them in production cars. The 15A was to be developed to go into the X110, an early design study for the RX-7. The 13A went into the RX-87 shown in the1968 Tokyo show, and detuned for the 1969 Luce displayed that year. My favourite the 21A was developed to go into a real mans car, a competitor for the Porsche 911. In addition there were several experimental and race engines such as the one for the 787.

toyo_kogyo

I found a 13A engine.

trochoid

iTrader: (6)

Don't tease, post pics of it.

toyo_kogyo

[IMG][/IMG]

[IMG][/IMG]

mazdaverx713b

iTrader: (91)

mmm delicious! but you're still teasing....