I picked up a '79 with a 13b swap. Can someone help me identify what year it is? Or at the very least if it is a 6 port or a 4 port. I'm replacing the header and I'd like to know what gasket to get without taking off the header. (Its a daily driver)

Thanks!

 

i'm going to guess '76-'78? my '74 has the same center housing but the rotor housings have the "MAZDA" in taller letters and framed.

 

'76-'77 REPU, I think. Jeff will probably correct me.

 

Jeff will know.

 

I think from the text on the casting above "Mazda" that they're 75-78. I know 74 had an italicized script with the Mazda slanted over and a frame around it. Likely 4-port, but someone may have gotten creative. Can you get a shot of the bottom area of the intake manifold?

 

Where's Jeff he would know

 

Thanks for the help. I'll try and get a look a photo of the bottom of the intake manifold.

 

You may have a bastard. The side plates are '74-'75 - no question about that. The rotor housings are J-spec from either a delivery van or the 26 passenger bus; The Parkway Rotary 26. You can tell by the "Automobiles" in raised letters next to the late '75 and all successive housings mazDa font.

I have a set of these housings which came from a vehicle with an auto-stick style transmission. It had a torque convertor filled with engine oil! It also had a 4 or 5 speed manual gearbox behind it. The torque convertor was fed oil through the rear of the eccentric shaft and returned to the engine at the lower right corner of the rear plate. The engine required a 'blind plug' and I had to drill out the steel sleeve, cut threads into th esurrounding iron and add an NPT plug. I could have used a freeze plug but chose the pipe plig instead.

The rotor housings have GSL-SE port timing, thermal reactor air bleed ports and you can use any spark plugs with them as they don't have the raised half circle or three aluminum spacers as the later housings do.

One problem with these engines is they were set up from the factory to run great at low to mid RPM but had small ports on the primaries with smallish castings taking a lot of time to port them out. I've never bothered as I've wound up using tall ported intermediate plates instead such as Y or the tall nitrided R5. Because your engine appears to have '74-'75 3B plates, all 4 ports should be '74 spec (that's like a small streetport - from the factory!). The 3B has short ports on the outside which can be confusing to some, so if you get a chance to remove your manifold, reach a finger inside and find out how tall your primaries are. Compare to your secondaries. There is a chance your engine may not be a bastard after all - it could be an early '75 van or bus engine where as mine was a late '75 or possibly early '76.

Also check the waterpump. If it has a green choke switch, it will also have a hot 190° thermostat (meant for keeping plugs clean at low speeds and reducing carbon buildup etc). There will be a funny internal bypass which is a springloaded valve that is possibly temperature controlled like the thermostat. It sits below the t-stat in the bypass hole. I've seen it in stock '76 Cosmo and '78 RX-4 waterpumps. I used a 180° stat in my Cosmo and a healthy clutch fan and the temps stay within a perfect range for me (you can feel it in the air exiting the heater core - especially when you get on it and the heat goes up lol).

So there you have it. A possible bastard or it possibly came stock that way. I don't know. At least with the 3B intermediate plate you're pretty much guaranteed to have '74 spec ports at a starting point and since I see a Holley on it, chances are someone went through the engine and ported it out even further. Perhaps that is why the rotor housings don't match the side plates.

I can't think of anything else. Oh, you'll need a '76-'78 exhaust gasket because it has the correct shape to prevent the thermal reactor ports from leaking. You can find it on the Mazdatrix website if you look real hard.

Spill your guts about the new exhaust you want to install. I think you owe me that much.

 

what is going on on top of the rear housing? looks like there might have been a coolant hose there?

 

Wow jeff, thank you for all that. I think its going to take a few reads to digest all that info. This car get odder and odder, I kinda like that

I'll get back to you on the water pump when I get home.

You asked about the exhaust Jeff, so I tell you what I know. It has some unknown header to a big old silencer (like 2 feet long!) then to a catalytic converter looking thing (with a pipe to a pump driven by the engine!?) THEN a custom pipe to a generic muffler jury rigged to the frame (welded) and BTW it is very very loud....

So... I'm replacing the entire thing with a Racing Beat header, pre-silencer and muffler. I also ordered a OEM connecting pipe. Plus all the hangers and gaskets and praying that everything fits!

Thank you again Jeff.

 

I'm sorry, I don't see what you are referring to.

 

Jeff I just noticed you are in Seattle too Cool beans.

 

thats old school. they used to run, header to a corvette cat, with the vetter air pump, and it'll pass smog that way.

this is back before you could just buy generic high flow cats