Replacement Engine Exhaust Ports
 

I am replacing a failed engine in my '79, but the replacement 12A engine has different exhaust porting. Just under the main exhaust ports on my '79 12A engine are a set of smaller ports. The replacement 12A does not have these. Can anyone tell me whether this is a problem I need to be worried about and what (if anything) I need to do to use the replacment engine in my '79? I have digital pictures of both I can send anyone who can help.

I am not 100% sure, but...

I believe the "extra" exhaust ports on the '79 have to do with the
Thermal Reactor that it normally uses. This was Mazda's attempt at
lowering emissions.

The 80+ engines don't have this since they use Exhaust Manifolds, Air-pumps, and more emissions control crap.

From what I understand, people who use Headers on 79/80 12A engines usually just cover those ports with the header flange anyway.

I wouldn't worry too much about it, since you are going to use the newer engine's rotor housings anyway.

Again, someone with more experience on these older 12A's should chime in and either confirm or deny my theory.


:D

Thanks for the info. Another concern I have to be worried about is passing emissions test here in Georgia.

that does pose a problem for emissions since the '79 doesn't use cats.

i'm not sure cause my car's emissions kinda fell off, but let's reason through this.
you could use the '85 manifold and an aftermarket cat. but that poses a few new problems. the bonez system uses a cat with an air supply tube. that means you would have to use the '85 intake with all the smog pump bullshit. yuck
the mazdatrix jobber i'm not sure about. it doesn't say if it uses an air supply tube or not on their website.
how strict are you emissions laws? if you are creative, there are always ways around them.

You need to get a '79 or '80 engine if you want to retain your current emissions system. If you want to convert to a catalytic converter, you need to get a complete '81-up engine including computer and wiring harness.

Easiest way to tell a '80-down from a '81-up 12A is the small air port under the exhaust ports like you described. The air injection port is under the exhaust ports on '80-down, and is under the center intake ports on '81-85 engines.

I'm really trying to get out of this as cheaply as possible and then sell the car. Can anyone tell me how to use the '81 engine on a '79. Maybe there is some workaround short of installing the later exhaust.