79+80_rx-7

Just curious if there is such thing as a 3 rotor 12a. I did a search for about 3 hrs and just can't find anything on them! Anybody know of a 3 rotor 12a, just curious if they exsist. THANKS!!
LATERZ,
Andrew

abeomid

it wouldn't be 12a anymore

peejay

Mazda never made a 3-rotor using 12A rotor dimensions. (which would make it an 18A)

They did make a 4-rotor research engine displacing, I think either 1.0 or 1.2l, as well as a 6A research engine which was a one-rotor of 12A rotor dimensions.

They also had plans for a 15A shortly before the first oil crunch, as well as "big block" 21A and 22A engines for their stillborn sports car atemptin the early 70's, to compete with the 240Z. The 15A was a 13B with 10mm wider rotors (just like a 13B is a 12A with 10mm wider rotors, and a 12A is a 10A etc.) and interestingly enough, torque improves out of proportion to displacement as they'd make the rotors wider, indicating that the wider rotor engines have better efficiency. The 21/22A engines had different rotor/trochoid dimensions entirely - they had a bigger "diameter" as well as wider rotors.

I'm surprised they never went ahead and made the 15A... with its greater efficiency they might have been able to get even better MPG out of it compared to a 13B of the same power level.

79+80_rx-7

What would it be called????? I was just wondering!! LATERZ,
Andrew

peejay

Mazda has a funny way of naming their rotary engines. The first one of a certain displacement is an "A" engine. (eg. 10A is first 1-liter, 12A is first 1.2l (actually 1.146 but they rounded up). There was a 13A, used only in the FWD R-130. (Yes a FWD rotary!) To make it short enough to work they didn't make the rotors wider, instead they made the "diameter" larger. The second 1.3l they made, the 13B, is based on the "normal" dimensions.

Interestingly enough, they were going to change the name of the 12A to 12B in '74 because they made dramatic changes to the design - went to a totally different kind of rotor sealing system, went to a single distributor vs. the old "twin dizzy" setup, etc. but they kept the 12A name for market recognition.

So why is the 20B a "B" engine? Partly because when it was in production, all rotaries being made were 13Bs (that whole market recognition thing) but also because there already was a 2.0l 3-rotor - the 13G. (Why they called it a 13G instead of 20A I'll never know)

79+80_rx-7

So 13b had wider rotors than the 12a??? And the 12a had wider rotors of the 10a??? So it all goes back to Pontiac, "WIDER IS BETTER"? Would I be better off with a 20b rather than an 18a??? What would be the difference hp/tq whise? Just thought I might play with a 3 rotor 12a ! But would need a lot of parts Oh well still might THANKS
LATERZ,
Andrew

madaz07

ive seen a 3 rotor 12a. i know i didnt beleive it at first i thought it was a 20b then i was told to have a closer look and there it was 12a on all three housings i was like

peejay

that "18A" was a custom job then... cool though

MIKE-P-28

iTrader: (1)

I thought the A and B stood for the seal configuration on the rotors, or I remember reading that on racing beats site or something quite a while ago

peejay

Nope... '74-85 12A and pre-86 4-port 13B are almost identical internally, in fact the side housings are interchangeable, as are all rotor seals and gaskets and parts that don't pertain to engine length. If you have a 13B E-shaft, rotors, rotor housings, and the manifolds, you could make a 4-port 13B using a 12A for the rest of the hardware. Likewise you could put GSL-SE end irons on a 12A and make a 6-port 12A, good luck finding an intake manifold for it though! (maybe you can get someone from Australia to ship you one - carby 6PI 12As were used in some Japanese cars)

Magnus Berglund

Hurley engineering in the UK makes 3 rotor's based on the 12A....
http://www.hurley-engineering.ltd.uk/index.htm

It's not a 12A as pointed out.. but the closest you can get!

//Magnus

smnc

Actuall the 12A should be an 11A, and the 3 rotor version would be a 17A I think...

Anyways, the A and B has to do with the ecentricity and generating radius of the engine, basically the internal dimentions of the engine.

Check this: http://mrmazda.members.atlantic.net/cfaqtext.html

PaulFitzwarryne

The 3 rotor engine seen by Mazda07 I think is in the RX-7 owned by The Hitman. A full description of the car and engine photos are on his web site. In street trim it puts out 650bhp.

PaulFitzwarryne

SMNC as discussed with you on another thread, the cubic capacity of the 12a rounds out to 1.2 litresas the convention while approximating of 0-4 being rounded down and 5-9 being rounded up by digit sequence.

However, the method of calculating capacity of a rotary engine was chosen to minimise the taxation paid. Its the average between the maximum capacity and minimum capacity of each chamber multiplied by the number of chambers. In comparison, using the piston engine approach a 12a would be 2.3 litres.

If you want to split hairs there is a good argument for the engine to be called a 12A as in the original Japanese specification! At least in Gen 1 circles we do not have to argue about the spelling of Anfini.

peejay

Oh well, 1146cc = 1.2l, I suppose just like 4948cc = 5.0l.

Hmm... 573 X 3 = 1719. So I guess it would be a 17A then eh? But we could call it an 18A just to keep Mazda's scheme going strong

smnc

My thinking exactly peejay

Node

iTrader: (1)

great sig

SoRRoW

Hows this

pratch

am I the only one that finds that strangely erotic?

79+80+84_rx-7

node~ nice sig? what?
Why the thread from the dead? hehe


Thats a cool picture, thanks...

got any more?

smile444

you're the only one pratch! : )

MikeLMR

ignore me please (wrong thread)

79+80+84_rx-7

Ignor me too!

GlobalSport

Where would one find a 12A-based three rotor or four rotor e-shaft?

vipernicus42

iTrader: (4)

You have to get it custom machined.

Aaron Cake in the Canadian forum is getting a custom e-shaft for a funky special project he's doing.... But 20b e-shafts can be bought, since 20bs are more common now.

Jon