Motor difference between years??

one320fc · 06-13-2011, 12:53 PM

I was looking at RBs ignition spread sheet and it calls for different timing between 79-83 and 84-85 12A

djmtsu · 06-13-2011, 04:06 PM

Might have something to do with the older points style dizzy's versus the electronic ones.

Just a guess.

one320fc · 06-13-2011, 05:43 PM

Yea thats what I was thinking but figured I would ask..

2gslse · 06-13-2011, 10:29 PM

I think it is mostly due to the rotors on the later 12A's had a different shape to the bathtub section the rotors are front and rear and not interchangeable if I remember correctly.

t_g_farrell · 06-14-2011, 08:03 AM

Could be the different shape as mention, plus the later rotors are lighter as well.

Other factors are the intake/exhaust stock port shapes and maybe plug
placement. Not sure on that last because they roughly look to be at the same
place on the housings.

one320fc · 06-14-2011, 05:27 PM

Damn thats pretty cool! I didnt realize there was that much difference in the 12As If im not mistaken hp stayed the same on the 12As??

PercentSevenC · 06-19-2011, 12:27 AM

Port timing is the same for all U.S. spec '79+ 12As as far as I'm aware, as is plug placement. There were some variations in carbs and intake manifolds over the years. '79 had a points distributor, '80 had an early style electronic dizzy, and '81-85 dizzys are largely the same except for the GSL-SE which had a different advance curve. '83-85 had a lighter rotating assembly and the beehive oil cooler. '79-80 had the "thermal reactor" exhaust manifold and there are some minor casting differences. I don't remember for sure whether the oil pumps changed during the first-gen era (I know Racing Beat's website has some incorrect information regarding oil pumps); ask Jeff20B, he'd know.

Just a quick rundown off the top of my head. If I made a mistake, someone feel free to correct me.

85rx-7gsl-se · 06-19-2011, 09:49 AM

You mean gsl? Gsl-se has a 13b as you know.

PercentSevenC · 06-25-2011, 03:55 PM

Quote:

Originally Posted by 85rx-7gsl-se

You mean gsl? Gsl-se has a 13b as you know.

No, I mean GSL-SE. They had distributors, too, you know. Only the fuel was controlled by the ECU. Same with the 12AT, except the 12AT distributor had some sort of boost-retard function. I'm not too familiar with them.

85rx-7gsl-se · 06-25-2011, 06:45 PM

Yeah but this thread about 12a's lol so I was just trying to clarify. I figured you knew the gslse had a 13b :-P

j9fd3s · 06-25-2011, 07:55 PM

the 12A evolves a bit over the years, sometimes in totally unimportant ways.

74-75 12A's have the big port, intake closes @50 instead of 40, exhaust closes i think @48 instead of 38 degrees. the rotor housings have the big font MAZDA on them. irons are non nitrided and painted black. rotors are MDR like a 13B

76-78 12A. these get the smaller port, which the 12A keeps in the us, until 85. rotor housings are the "mazda automobiles" ones. irons are still non nitrided, and black. rotors become LDR. the 76-78 parts basically superseded to the 79 spec.

79-80 12A. basically the same as the 76-78, except the irons get nitrided. in 1980 they went from 18 to 17 tension bolts.

81-82 12A. new rotor housings for the catalyst exhaust. lighter flywheel, its like 21# instead of 30#.

83-85 12A. the rear iron gets a T heater hose connection for the beehive. the rotors are lighter. oil pump is the bigger one.

crib notes.

front, middle iron, eshaft and stat gears interchange from 76-85. rear iron is either 83-85 or 76-82. rotor housings are 76-80 or 81-85, reactor or cat. rotors are 76-82 (these have a F or R stamp), 83-85 (NF or NR stamp). flywheel is 76-80, 81-82 (same balance but lighter) and 83-85.

this is ONLY for the US, the rest of the world is slightly different after like 79-80. some markets keep the reactor, some markets got bigger ports, etc etc

-xlr8planet- · 07-25-2011, 04:53 PM

Great thread

I think I have a set of 83-85 rotors. What flywheel and counterweight do I have to use with those?

j9fd3s · 07-26-2011, 01:16 PM

Quote:

Originally Posted by -xlr8planet-

Great thread

I think I have a set of 83-85 rotors. What flywheel and counterweight do I have to use with those?

there are 2 different 83-85 rotors.

the non turbo ones are stamped NF for front and NR for rear, right in the combustion recess

the turbo ones are TF and TR.

you need the 83-85 front counterweight, N225 off the top, and the flywheel is an N249/N231 again off the top.

-xlr8planet- · 07-26-2011, 01:52 PM

Thanks man

I will take a look at the ones I have

06-13-2011, 12:53 PM	#1
one320fc one Apex @ a time Join Date: Feb 2008 Location: Culpeper VA iTrader: (1) Posts: 272 Rep Power: 17	Motor difference between years?? I was looking at RBs ignition spread sheet and it calls for different timing between 79-83 and 84-85 12A __________________ 1983 Limited Edition SOLD 1977 Mazda REPU I will work on it one day I sware!! 1987 T2 um after the repu is done?? 2013 Chrysler 200 DD 2009 Dodge Journey 94 Volvo 850 N/A The slowest car I have EVER owned!!!

06-13-2011, 04:06 PM	#2
djmtsu My minds tellin' me no... Join Date: Feb 2008 Location: Murfreesboro, TN iTrader: (10) Posts: 4,043 Rep Power: 21	Might have something to do with the older points style dizzy's versus the electronic ones. Just a guess. __________________ 1976 Mazda Cosmo RX-5 1976 Mazda Cosmo RX-5 2003 Toyota Tundra TRD 2015 Toyota 4Runner SR5

06-13-2011, 05:43 PM	#3
one320fc one Apex @ a time Join Date: Feb 2008 Location: Culpeper VA iTrader: (1) Posts: 272 Rep Power: 17	Yea thats what I was thinking but figured I would ask.. __________________ 1983 Limited Edition SOLD 1977 Mazda REPU I will work on it one day I sware!! 1987 T2 um after the repu is done?? 2013 Chrysler 200 DD 2009 Dodge Journey 94 Volvo 850 N/A The slowest car I have EVER owned!!!

06-13-2011, 10:29 PM	#4
2gslse Rotary Fanatic Join Date: Apr 2008 Location: front royal va iTrader: (0) Posts: 440 Rep Power: 17	I think it is mostly due to the rotors on the later 12A's had a different shape to the bathtub section the rotors are front and rear and not interchangeable if I remember correctly. __________________ ____________________________________________ 1976 Cosmo needing lots of work 1993 Rx-7 410 RWHP single turbo toy 1985 Rx-7 toy/project car 411HP stoplight terror 2001 Dodge ram 4wd.parts hauler 2016 Ram 2500 cause its a hemi 2006 VW TDI commuter __________________________________________ I guarantee there's a pregnant redneck teenager somewhere in a shitty trailer park that thinks "Ebola would be a lovely name for their child"...

06-14-2011, 08:03 AM	#5
t_g_farrell Waffles - hmmm good Join Date: Aug 2008 Location: Huntersville, NC iTrader: (0) Posts: 757 Rep Power: 0	Could be the different shape as mention, plus the later rotors are lighter as well. Other factors are the intake/exhaust stock port shapes and maybe plug placement. Not sure on that last because they roughly look to be at the same place on the housings. __________________ 1980 GS stockport, Fat Nikki, RB Dual Facetfuel pumps, Holley regulator, RB Street port exhaust, 2GDFIS, MR2 MK I electric fans, 2G strut bar, relayed fans, lights and fuel pump, LEDs Project Fat Nikki Budget 12A rebuild Video setup < $30.00

06-14-2011, 05:27 PM	#6
one320fc one Apex @ a time Join Date: Feb 2008 Location: Culpeper VA iTrader: (1) Posts: 272 Rep Power: 17	Damn thats pretty cool! I didnt realize there was that much difference in the 12As If im not mistaken hp stayed the same on the 12As?? __________________ 1983 Limited Edition SOLD 1977 Mazda REPU I will work on it one day I sware!! 1987 T2 um after the repu is done?? 2013 Chrysler 200 DD 2009 Dodge Journey 94 Volvo 850 N/A The slowest car I have EVER owned!!!

06-25-2011, 07:55 PM	#11
j9fd3s Rotary Fanatic Join Date: Mar 2008 iTrader: (0) Posts: 123 Rep Power: 17	the 12A evolves a bit over the years, sometimes in totally unimportant ways. 74-75 12A's have the big port, intake closes @50 instead of 40, exhaust closes i think @48 instead of 38 degrees. the rotor housings have the big font MAZDA on them. irons are non nitrided and painted black. rotors are MDR like a 13B 76-78 12A. these get the smaller port, which the 12A keeps in the us, until 85. rotor housings are the "mazda automobiles" ones. irons are still non nitrided, and black. rotors become LDR. the 76-78 parts basically superseded to the 79 spec. 79-80 12A. basically the same as the 76-78, except the irons get nitrided. in 1980 they went from 18 to 17 tension bolts. 81-82 12A. new rotor housings for the catalyst exhaust. lighter flywheel, its like 21# instead of 30#. 83-85 12A. the rear iron gets a T heater hose connection for the beehive. the rotors are lighter. oil pump is the bigger one. crib notes. front, middle iron, eshaft and stat gears interchange from 76-85. rear iron is either 83-85 or 76-82. rotor housings are 76-80 or 81-85, reactor or cat. rotors are 76-82 (these have a F or R stamp), 83-85 (NF or NR stamp). flywheel is 76-80, 81-82 (same balance but lighter) and 83-85. this is ONLY for the US, the rest of the world is slightly different after like 79-80. some markets keep the reactor, some markets got bigger ports, etc etc

07-25-2011, 04:53 PM	#12
-xlr8planet- RCC Contributor Join Date: Feb 2008 Location: Buenos Aires, Argentina iTrader: (4) Posts: 679 Rep Power: 17	Great thread I think I have a set of 83-85 rotors. What flywheel and counterweight do I have to use with those? __________________ www.rx7club.com.ar RX-7 Forum in Spanish I make custom decals. Yes, you can ask me

07-26-2011, 01:52 PM	#14
-xlr8planet- RCC Contributor Join Date: Feb 2008 Location: Buenos Aires, Argentina iTrader: (4) Posts: 679 Rep Power: 17	Thanks man I will take a look at the ones I have __________________ www.rx7club.com.ar RX-7 Forum in Spanish I make custom decals. Yes, you can ask me

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