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Hi,
I'm in the process of replacing the o-rings and the intake manifold gasket. A gasket ordered for 78-80 cars did not fit, but one for 81-85 cars did. I've read on the forum that some engines are cobbled together from several years of different parts. I just want to clearly understand what I have for future parts orders. The car has oil cooler, points in the dizzy, and has been de-smogged (rats nest and air pump is gone). Spark plugs do not have "eyebrows" above and below each spark plug.
Pics show a rectangular port below the two centre ports that does not show on the intake manifold..seems odd.
Everything I see points to a 79-80 SA. The odd thing about your intake manifold is that it appears that the lower rectangular exhaust port his missing. That carb looks fairly stripped down from what I can see.
That's the same set up that was in my 79 when I got it. I didn't realize until much later in my build that I had a center iron with the rectangular port that was not covered over by the intake manifold, and then I understood why there was such a LOUD noise coming from that side of the engine. To me it sounded like an old radial airplane engine. Wonder if you noticed that yours was similarly loud?
From what I've learned (and others more knowledgeable than me can correct me), the intake manifold you have is early (79 - 80) 12A, and the center iron of that engine appears to be from later than 80. That is a desirable intake manifold too... Nice and simple yet has lots of airflow.
If you look at the top of the aluminum housings, near where the rats nest would have been bolted down to the top of the engine, you should see in the aluminum castings either an "H" pattern or a square pattern. There should be one on each housing, and unless the engine was cobbled together they should be the same. Of course, they could be the same and the engine could still be cobbled together. If you have two "H"'s then your engine is likely other than a 79 - 80. If they are sold squares, then your engine is likely a 79 - 80. I believe however, that the center iron you have there is from later than 79 - 80. I think in 81 they started with that square exhaust port.
The engine housings from my 79 and an 80 I have from a junkyard had the two solid squares. The two engines I have from 83 are both "H"'s.
Hope that helps! Again, there are others on here that have been in this business much longer than I have and can correct any of my mistakes. Banzai, Mazdadave, Divindriver, fungus mungus, and j9fd3s (to name a few) can reliably verify that info.
That's the same set up that was in my 79 when I got it. I didn't realize until much later in my build that I had a center iron with the rectangular port that was not covered over by the intake manifold, and then I understood why there was such a LOUD noise coming from that side of the engine. To me it sounded like an old radial airplane engine. Wonder if you noticed that yours was similarly loud?
That is spot on woodmv ^^^ I noticed my 12a sounds a bit like that plane engine, mine has that square exhaust port not blocked up same setup as above^^^.
Block it or leave it?
Does it make much difference to how the car sounds if blocked?
And how do you go about blocking it up without pulling the motor apart, a later model intake manifold?
That rectangular port is for emissions. It takes exhaust gas and ports it to the intake like an EGR system. On US 79-80 cars the port existed but was internally blocked thus no need to cover it. If you put a 79-80 intake manifold on a 81-85 engine you will create an exhaust leak. That is what the loud noise is.
That is spot on woodmv ^^^ I noticed my 12a sounds a bit like that plane engine, mine has that square exhaust port not blocked up same setup as above^^^. Block it or leave it? Does it make much difference to how the car sounds if blocked? And how do you go about blocking it up without pulling the motor apart, a later model intake manifold?
Yes, I imagine it does make a huge difference if it's left open vs. blocked off. I bought some quick steel to seal that port up on my replacement engine, but I've been collecting parts and also have a correct manifold and carb setup that I think I may use instead. Here's a pic of the quick steel;
That will fill that square port and you can use your 79/80 12A intake manifold.
Thank you very much for your super quick and detailed responses! I appreciate your expertise.
My car's first owner ran a racing school that used Mazda Rx-7's to teach with. I think he travelled between between Phoenix and Calgary Canada. It was his personal car and not raced. Apparently he had a fantastic Mazda mechanic working for him. The engine was really well de-smogged... no vacuum leaks and the engine runs exceptionally smoothly with very good power. The only visible mods are RB header and exhaust, so it looks really stock. No loud noise from the square port. I suspect there are other things done to increase performance on this engine, but being a noobie to the rotary engine, I;m not sure how to spot them.
woodmv, I appreciate your detailed response. Good to know about the intake manifold. The rotor housings have the small square, no "H".
Is the centre section a different width from year to year? Could that account for a 78-80 intake gasket not fitting?
That rectangular port is for emissions. It takes exhaust gas and ports it to the intake like an EGR system. On US 79-80 cars the port existed but was internally blocked thus no need to cover it. If you put a 79-80 intake manifold on a 81-85 engine you will create an exhaust leak. That is what the loud noise is.
So the rectangle port sucks in exhaust gases/emissions into the intake?
The exhaust system on my car is fairly rusted in spots that's where I thought the leak was coming from but i don't think it's effecting performance too much car still goes good.
Yes, I imagine it does make a huge difference if it's left open vs. blocked off. I bought some quick steel to seal that port up on my replacement engine, but I've been collecting parts and also have a correct manifold and carb setup that I think I may use instead. Here's a pic of the quick steel;
That will fill that square port and you can use your 79/80 12A intake manifold.
does it make a difference on performance too?
I read about the quicksteel/devcon method but thought the only way to use it was to tear the engine apart incase of the epoxy going through your motor.
what year is the proper manifold? I might do what you've done and use the right manifold.
Thanks for the info too woodmv.
Thank you very much for your super quick and detailed responses! I appreciate your expertise.
My car's first owner ran a racing school that used Mazda Rx-7's to teach with. I think he travelled between between Phoenix and Calgary Canada. It was his personal car and not raced. Apparently he had a fantastic Mazda mechanic working for him. The engine was really well de-smogged... no vacuum leaks and the engine runs exceptionally smoothly with very good power. The only visible mods are RB header and exhaust, so it looks really stock. No loud noise from the square port. I suspect there are other things done to increase performance on this engine, but being a noobie to the rotary engine, I;m not sure how to spot them.
woodmv, I appreciate your detailed response. Good to know about the intake manifold. The rotor housings have the small square, no "H".
Is the centre section a different width from year to year? Could that account for a 78-80 intake gasket not fitting?
The center section might be a bit wider in later years not 100% sure. I did a intake gasket last year some time and it all lined up nicely from memory, maybe the center plate was ported before assembly on your engine.
If you want to make your own intake gasket do it port by port doesn't have to be all one piece, just use a tiny bit of silicone to hold the gaskets in place while torquing the manifold back on if that makes sense lol.
you'd prolly make 2-3 intake gaskets with the one sheet of gasket paper.
So the rectangle port sucks in exhaust gases/emissions into the intake?
The exhaust system on my car is fairly rusted in spots that's where I thought the leak was coming from but i don't think it's effecting performance too much car still goes good.
Joe is wrong. No 1st-gen had an EGR system except for the '80 California model. Look on the top of the center housing for an EGR valve, if you do not have one, you do not have an '80 California model.
The bottom port in the center housing is for air injection. Air goes from the air pump to the ACV and the ACV sometimes directs it through that port down to the exhaust ports. IF you have an '81-85 12A. '79-80 12As had the ACV route air to the heat exchanger, which passed it along a very expensive and intricate dual-wall downpipe, then through ports in the thermal reactor, then through a pair of holes in the exhaust manifold flange which ran to passages in the exhaust ports.
What you have is an SA intake manifold and an FB engine. The emissions system will not work and you will have a major exhaust leak.
Thank you very much for your super quick and detailed responses! I appreciate your expertise.
My car's first owner ran a racing school that used Mazda Rx-7's to teach with. I think he travelled between between Phoenix and Calgary Canada. It was his personal car and not raced. Apparently he had a fantastic Mazda mechanic working for him. The engine was really well de-smogged... no vacuum leaks and the engine runs exceptionally smoothly with very good power. The only visible mods are RB header and exhaust, so it looks really stock. No loud noise from the square port. I suspect there are other things done to increase performance on this engine, but being a noobie to the rotary engine, I;m not sure how to spot them.
woodmv, I appreciate your detailed response. Good to know about the intake manifold. The rotor housings have the small square, no "H".
Is the centre section a different width from year to year? Could that account for a 78-80 intake gasket not fitting?
That's excellent that you have the history of the car! A lot of times that's the biggest mystery. Sounds like it was put together and maintained well.
I agree with mazdadave that it looks like you have a 79 - 80 engine. I suspect that the EGR port is covered over by the thermal reactor when it is built to stock specifications. With the header however, it becomes uncovered. Mine had a header also when I got it. Aside from the louder engine and some obnoxious fumes (if it's not otherwise blocked off) it's ok to run with it like that, unless you have to pass an emissions test maybe?
The obviously identified performance mods are the header and emissions delete. Not so easy to spot are the stripped carburetor, which you could identify by comparing yours to the FSM. Some people also hog out their intake manifolds.
Originally Posted by sandy_RE
does it make a difference on performance too?
I read about the quicksteel/devcon method but thought the only way to use it was to tear the engine apart incase of the epoxy going through your motor.
what year is the proper manifold? I might do what you've done and use the right manifold.
Thanks for the info too woodmv.
I don't think you have to tear down the engine to do the quicksteel mod, but it helps to have the engine out of the car. The stuff likes to bond to bare metal, so if I decide to got that way I'll rotate the engine so that side is down and prep the surfaces (sand or grind on them).
I believe the proper year manifold to cover the EGR port is 81-85 12A, since they stopped using the thermal reactor after 80.
I believe the proper year manifold to cover the EGR port is 81-85 12A, since they stopped using the thermal reactor after 80.
*sigh*
It is NOT an EGR port. No FBs had EGR. EGR ports wouldn't even be there on the engine anyway, if it was. There was no reason for Mazda to need EGR on the FBs because they started using catalytic converters, which could reduce NOx outside of the engine, instead of having to introduce exhaust gases to cool the combustion down, like they had to do to meet California specs in '80 before they had catalysts.
The emissions standards tightened up again for '86 and Mazda started using an EGR valve there again. But only on the nonturbo cars, the turbo cars had lower compression and naturally produced less NOx so no EGR was needed.
Joe is wrong. No 1st-gen had an EGR system except for the '80 California model. Look on the top of the center housing for an EGR valve, if you do not have one, you do not have an '80 California model.
The bottom port in the center housing is for air injection. Air goes from the air pump to the ACV and the ACV sometimes directs it through that port down to the exhaust ports. IF you have an '81-85 12A. '79-80 12As had the ACV route air to the heat exchanger, which passed it along a very expensive and intricate dual-wall downpipe, then through ports in the thermal reactor, then through a pair of holes in the exhaust manifold flange which ran to passages in the exhaust ports.
What you have is an SA intake manifold and an FB engine. The emissions system will not work and you will have a major exhaust leak.
I never said they have an EGR. I said it is a port connecting exhaust gas to the intake LIKE an EGR to explain why leaving it open on an 81+ will induce an exhaust leak. I did have the flow direction reversed but the result of leaving it open is the same. I couldn't remember at the time of post that it is called an ACV port like you and others pointed out so I simplified.
In case anyone wants to know how how that system works, here is a thread about it.
In my follow up post I incorrectly called it an EGR port - my bad! At any rate, as peejay said, SA intake on an FB engine. Can the port be filled? From what I've been told, yes, it can, and without taking the engine apart. Can you find a correct FB (81-85) manifold? Yes, you can.
Joe is wrong. No 1st-gen had an EGR system except for the '80 California model. Look on the top of the center housing for an EGR valve, if you do not have one, you do not have an '80 California model.
The bottom port in the center housing is for air injection. Air goes from the air pump to the ACV and the ACV sometimes directs it through that port down to the exhaust ports. IF you have an '81-85 12A. '79-80 12As had the ACV route air to the heat exchanger, which passed it along a very expensive and intricate dual-wall downpipe, then through ports in the thermal reactor, then through a pair of holes in the exhaust manifold flange which ran to passages in the exhaust ports.
What you have is an SA intake manifold and an FB engine. The emissions system will not work and you will have a major exhaust leak.
There's no EGR valve on the car the previous owner removed it along with the charcoal canister and other bits and pieces. Iv always wanted to sort out the rats nest and solenoid rack but it gets confusing with all the bits missing. It's not a California model it's a Savana series 1 rx7 I'm pretty sure as it has the three hatch sill drain holes not 2 and the speedo on the cluster goes up to 180kph not 210kph like Australian delivered models.
when I first got the car the secondary's never worked till a few days after I noticed the pipe coming off the air pump was blocked with a solid pipe, I removed it and the secondary's have worked ever since (I'm not sure if it was so nobody could thrash the car on a test drive, or to save on fuel or maybe whoever removed bits and pieces from the rats nest didn't know what they were doing).
One pipe of the ACV goes to the blue air filter, and the other goes under the air pump but isn't connected to anything it just has a solid pipe wedged in held by a clamp lol.
I know the pipe your talking about its real skinny and runs alon side the stock exhaust.
There's no heat exchanger or thermal reactor on the car.
It's a 2.5 inch system(way too big for a Stockport 12a lol but the guy I got it off you to take it to the track for racing every now and then) it has headers, to a cat I think, a resonator then over the diff to rear muffler wich has seen better days lol.
I thought it was a FB engine as well , but I read around about the eyebrow over the spark plug holes means it's series 1 housings maybe it's series 1 housings with a later model 12a centre plate? Your right there's a massive leak the cars just too loud for a stockport and this thread explains a lot.
In my follow up post I incorrectly called it an EGR port - my bad! At any rate, as peejay said, SA intake on an FB engine. Can the port be filled? From what I've been told, yes, it can, and without taking the engine apart. Can you find a correct FB (81-85) manifold? Yes, you can.
Stupid question... But the the Nikki 4 barrel I got will bolt onto the later model manifold yea?
Here's more info on engine difference between the years
I found this information on this forum somewhere years ago and saved it (along with about 30 pages of other stuff) in a Word document. Just kept researching and researching, and copying stuff I thought was interesting. Take this for what it's worth, just stuff I found on here that someone had posted that I copied and saved. Fair warning: it has the three letter word EGR in it. I didn't save the username of the poster so I cannot attribute it to anyone in particular.
Here goes:
ENGINE DIFFERENCE THROUGH THE YEARS (79-85)
there are several ways to ID an engine.
the Rx7 engines are the first with nitrided side irons, so these should be grey in color, the earlier engines were just iron painted black.
the 79 model year engines had cream colored pulleys, 19 tension bolts, a screw in heater hose adaptor. the rotor housings have ribs front to back on them. the rotors are LDR type, with an F or R cast in the combustion recess (front or rear)
the 80 model year engines have 18 tension bolts. late in the run the pulleys are black. California has an oddball center iron and rotor housings for an EGR system.
in 1981 the engines got revised for the catalyst, the rotor housings are smooth on top with a thing that kind of looks like an H on top. the air injection passages are different. apex seals were redesigned as well. the flywheel goes from 30# to 22#
1982 is the same, although at some point the heater hose adaptor goes from a screw in fitting to a pressed in fitting.
in 1983-85 things change again, the rotors get redesigned, they will now say N F or N R, presumably the turbo rotors have a TF and TR. the heater hose fitting becomes a T for the oil to water oil cooler (beehive). flywheel gets heavier to about 24#, the rotors are lighter, so the net rotating weight is the same.
I found this information on this forum somewhere years ago and saved it (along with about 30 pages of other stuff) in a Word document. Just kept researching and researching, and copying stuff I thought was interesting. Take this for what it's worth, just stuff I found on here that someone had posted that I copied and saved. Fair warning: it has the three letter word EGR in it. I didn't save the username of the poster so I cannot attribute it to anyone in particular.
Here goes:
ENGINE DIFFERENCE THROUGH THE YEARS (79-85)
there are several ways to ID an engine.
the Rx7 engines are the first with nitrided side irons, so these should be grey in color, the earlier engines were just iron painted black.
the 79 model year engines had cream colored pulleys, 19 tension bolts, a screw in heater hose adaptor. the rotor housings have ribs front to back on them. the rotors are LDR type, with an F or R cast in the combustion recess (front or rear)
the 80 model year engines have 18 tension bolts. late in the run the pulleys are black. California has an oddball center iron and rotor housings for an EGR system.
in 1981 the engines got revised for the catalyst, the rotor housings are smooth on top with a thing that kind of looks like an H on top. the air injection passages are different. apex seals were redesigned as well. the flywheel goes from 30# to 22#
1982 is the same, although at some point the heater hose adaptor goes from a screw in fitting to a pressed in fitting.
in 1983-85 things change again, the rotors get redesigned, they will now say N F or N R, presumably the turbo rotors have a TF and TR. the heater hose fitting becomes a T for the oil to water oil cooler (beehive). flywheel gets heavier to about 24#, the rotors are lighter, so the net rotating weight is the same.
got off the phone to a rotary mechanic I was going to get the correct manifold off just before, he reckons my motor doesn't need the rectangle port blocked as it's not doing anything, so it must be my exhaust with a massive leak.
The correct model manifold is a earlier rx2 rx3 12a single dizzy intake.
I was chatting to him about blockng up the port, a tip from him if you don't want to use the right manifold is put heaps off high temp silicone in first leaving space to put the quicksteel/devcon to make it easier so it won't fall in to the bottom of the center plate.
got off the phone to a rotary mechanic I was going to get the correct manifold off just before, he reckons my motor doesn't need the rectangle port blocked as it's not doing anything, so it must be my exhaust with a massive leak.
Yes, your exhaust has a massive leak. It's at the rectangle port under the intake ports!
I'm done with the EGR. EGR engines did not have the rectangle port, they had a round core plug and the EGR valve mounted to the angled flat boss on the top of the intermediate housing. The core plug was there for process engineering reasons, to cover up the area where the drillings had to be made to connect passages together. If your engine had that, it originally had EGR and you need an EGR blockoff plate on the top of the engine. if it had a rectangle passage, it did not have EGR and you need to cover that rectangle somehow to prevent a massive exhaust leak.
Yes, your exhaust has a massive leak. It's at the rectangle port under the intake ports!
I'm done with the EGR. EGR engines did not have the rectangle port, they had a round core plug and the EGR valve mounted to the angled flat boss on the top of the intermediate housing. The core plug was there for process engineering reasons, to cover up the area where the drillings had to be made to connect passages together. If your engine had that, it originally had EGR and you need an EGR blockoff plate on the top of the engine. if it had a rectangle passage, it did not have EGR and you need to cover that rectangle somehow to prevent a massive exhaust leak.
I trust what he said but it was over the phone so he may of got it wrong.
how could I block it off without tearing the motor apart? with the silicone and some devcon/steel putty? Iv always wondered why the car sounded like rubbish but always thought it was the massive exhaust on a Stockport was the reason.
The rectangle port should be blowing if it's a leak, ill have a feel around when I go to start the car next and see what it's doing.
Back in the early 1980's I bought my first RX-7. A 1980 gold GS. It had a bad motor and I swapped a 1982 engine. I had the sake issue with the square port. I fixed it with JB Weld putty. It worked great. One of the strongest engines I've had.
Knowing what I know now, it probably would have been best to swap a 1982 intake. Since you have a header, I'd find the correct engine intake and just block off the ACV on the manifold with a block off plate.
08-12-16, 09:28 PM
What year of engine do I have?
