Does anyone understand the stock 79-80 exhaust system?
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Joined: Mar 2005
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From: Massachusetts
Does anyone understand the stock 79-80 exhaust system?
Hey guys,
Yesterday afternoon I dug into my new 79 GS that I got back in October.It is bone stock,right down to the tires,and has not run in 5 years.The PO told me when he last drove it that it was idling fine,but could not rev much higher than 3k rpm.I thought maybe an obstruction in the exhaust,and I plan on using my racing beat full dual exhaust anyway,so I started puling the original system out.To my surprise no one bolt or nut gave me any issues,or broke.the only thing wrong with the exhaust I can se is the small pipe that runs along side the exhaust system,and the muffler was rotted away,and missing where it goes over the rear axle.I am guessing this exhaust could be used by someone else if I don't hold on to it myself,so I can keep all the stock stuff.
My question is what the hell do all of these pipes in this system do under there?What is the deal with the exhaust manifold/thermal reactor thing,with the rotor shaped flange,and holes around its edge that look like the allow air to flow through from the air pump,and air control valve?Any help/insight would be appreciated.Thanks in advance.
Chris
Yesterday afternoon I dug into my new 79 GS that I got back in October.It is bone stock,right down to the tires,and has not run in 5 years.The PO told me when he last drove it that it was idling fine,but could not rev much higher than 3k rpm.I thought maybe an obstruction in the exhaust,and I plan on using my racing beat full dual exhaust anyway,so I started puling the original system out.To my surprise no one bolt or nut gave me any issues,or broke.the only thing wrong with the exhaust I can se is the small pipe that runs along side the exhaust system,and the muffler was rotted away,and missing where it goes over the rear axle.I am guessing this exhaust could be used by someone else if I don't hold on to it myself,so I can keep all the stock stuff.
My question is what the hell do all of these pipes in this system do under there?What is the deal with the exhaust manifold/thermal reactor thing,with the rotor shaped flange,and holes around its edge that look like the allow air to flow through from the air pump,and air control valve?Any help/insight would be appreciated.Thanks in advance.
Chris
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Joined: Dec 2003
Posts: 287
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From: Knoxville, Tennessee
The little pipe that runs along the exhaust system carries from the air pump to cool the thermal reactor and heat exchanger. I doubt any problem with this pipe would cause a lack of power.
FB+FC=F-ME
Joined: Jul 2004
Posts: 3,353
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From: Rohnert Park CA
The catylitic convertor looking thing is actually a heat exchanger that preheats the air from the smog pump,before its injected into the reactor.This allows the oxygen to be used by the reactor without lowering the internal temperatures, because the injected air is hot.
The small pipe that runs the length of the car is the dump tube for hot air that is pumped around the outer jacket of the thermal reactor.This system is used to prevent overheating of the reactor,which can cause meltdown.
The whole concept of the thermal reactor is very simple,and it actually works quite well to reduce smog emissions.Its just a really hot exhaust manifold that can oxidize smog pollutants within it's walls, simply with heat and some injected air.No catylist material is needed to help it out.Unfortunately keeping the reactor within its optimal operating temperature is complicated,hence all the extra gear just mentioned.Too much heat/oxygen and the reactor can burn out and collapse,cause massive exhaust restriction and loss of power.Too much airflow or a failed heat exchanger and the internal temps will drop and smog numbers will rise outside of allowable parameters.
The reactor and its associated systems are also heavy.If you can ditch them and not worry about smog,you can remove over 75lbs of stuff from the car by running a header or full exhaust system.
As far as power losses,the reactors are known for melting down internally,same goes with the mufflers.Check them out or replace them altogether to get your power back.Also,it would be best to replace the old style points ignition with an 81-85 electronic unit.It will save you a bit of tuneup maintenence and you can ditch the trailing spark cut feature which is only needed to keep the thermal reactor hot(feeds raw fuel into the reactor under certain conditions)
Later model 12A engines are called,"lean burn" because they dont have to provide the thermal reactors with excess fuel to keep them hot and burning.The reduction in fuel consumption and weight by dropping the 79 style exhaust,ignition and fuel delivery systems is substantial....
The small pipe that runs the length of the car is the dump tube for hot air that is pumped around the outer jacket of the thermal reactor.This system is used to prevent overheating of the reactor,which can cause meltdown.
The whole concept of the thermal reactor is very simple,and it actually works quite well to reduce smog emissions.Its just a really hot exhaust manifold that can oxidize smog pollutants within it's walls, simply with heat and some injected air.No catylist material is needed to help it out.Unfortunately keeping the reactor within its optimal operating temperature is complicated,hence all the extra gear just mentioned.Too much heat/oxygen and the reactor can burn out and collapse,cause massive exhaust restriction and loss of power.Too much airflow or a failed heat exchanger and the internal temps will drop and smog numbers will rise outside of allowable parameters.
The reactor and its associated systems are also heavy.If you can ditch them and not worry about smog,you can remove over 75lbs of stuff from the car by running a header or full exhaust system.
As far as power losses,the reactors are known for melting down internally,same goes with the mufflers.Check them out or replace them altogether to get your power back.Also,it would be best to replace the old style points ignition with an 81-85 electronic unit.It will save you a bit of tuneup maintenence and you can ditch the trailing spark cut feature which is only needed to keep the thermal reactor hot(feeds raw fuel into the reactor under certain conditions)
Later model 12A engines are called,"lean burn" because they dont have to provide the thermal reactors with excess fuel to keep them hot and burning.The reduction in fuel consumption and weight by dropping the 79 style exhaust,ignition and fuel delivery systems is substantial....
Thread Starter
Joined: Mar 2005
Posts: 1,584
Likes: 1
From: Massachusetts
Originally Posted by steve84GS TII
The catylitic convertor looking thing is actually a heat exchanger that preheats the air from the smog pump,before its injected into the reactor.This allows the oxygen to be used by the reactor without lowering the internal temperatures, because the injected air is hot.
The small pipe that runs the length of the car is the dump tube for hot air that is pumped around the outer jacket of the thermal reactor.This system is used to prevent overheating of the reactor,which can cause meltdown.
The whole concept of the thermal reactor is very simple,and it actually works quite well to reduce smog emissions.Its just a really hot exhaust manifold that can oxidize smog pollutants within it's walls, simply with heat and some injected air.No catylist material is needed to help it out.Unfortunately keeping the reactor within its optimal operating temperature is complicated,hence all the extra gear just mentioned.Too much heat/oxygen and the reactor can burn out and collapse,cause massive exhaust restriction and loss of power.Too much airflow or a failed heat exchanger and the internal temps will drop and smog numbers will rise outside of allowable parameters.
The reactor and its associated systems are also heavy.If you can ditch them and not worry about smog,you can remove over 75lbs of stuff from the car by running a header or full exhaust system.
As far as power losses,the reactors are known for melting down internally,same goes with the mufflers.Check them out or replace them altogether to get your power back.Also,it would be best to replace the old style points ignition with an 81-85 electronic unit.It will save you a bit of tuneup maintenence and you can ditch the trailing spark cut feature which is only needed to keep the thermal reactor hot(feeds raw fuel into the reactor under certain conditions)
Later model 12A engines are called,"lean burn" because they dont have to provide the thermal reactors with excess fuel to keep them hot and burning.The reduction in fuel consumption and weight by dropping the 79 style exhaust,ignition and fuel delivery systems is substantial....
The small pipe that runs the length of the car is the dump tube for hot air that is pumped around the outer jacket of the thermal reactor.This system is used to prevent overheating of the reactor,which can cause meltdown.
The whole concept of the thermal reactor is very simple,and it actually works quite well to reduce smog emissions.Its just a really hot exhaust manifold that can oxidize smog pollutants within it's walls, simply with heat and some injected air.No catylist material is needed to help it out.Unfortunately keeping the reactor within its optimal operating temperature is complicated,hence all the extra gear just mentioned.Too much heat/oxygen and the reactor can burn out and collapse,cause massive exhaust restriction and loss of power.Too much airflow or a failed heat exchanger and the internal temps will drop and smog numbers will rise outside of allowable parameters.
The reactor and its associated systems are also heavy.If you can ditch them and not worry about smog,you can remove over 75lbs of stuff from the car by running a header or full exhaust system.
As far as power losses,the reactors are known for melting down internally,same goes with the mufflers.Check them out or replace them altogether to get your power back.Also,it would be best to replace the old style points ignition with an 81-85 electronic unit.It will save you a bit of tuneup maintenence and you can ditch the trailing spark cut feature which is only needed to keep the thermal reactor hot(feeds raw fuel into the reactor under certain conditions)
Later model 12A engines are called,"lean burn" because they dont have to provide the thermal reactors with excess fuel to keep them hot and burning.The reduction in fuel consumption and weight by dropping the 79 style exhaust,ignition and fuel delivery systems is substantial....
Thanks for the lengthy reply.I understand it alot more now.What else I am wondering is will my header fuly cover the small exhaust lloking holes under the main exhaust ports on the block.It looks like they will,but I am not sure.
I planned on removing the stock system in favor of my header,and dual exhaust system,because in strict Massachusetts a car that was built in 1983 or older is exempt from emissions testing.I also plan on upgrading to the electronic ignition as well,but I want to make sure I can do it without cutting up the wiring.I want to be able to go back to stock at some point in time if I can,because this car is so complete,and perfect.Do you guys have a link to some instructions on how to upgrade to just the 81-85 ignition?I have seen plenty of dirct fire systems,but I think I will just be going conservative.Thanks again.
Chris
Full Member
Joined: Jun 2005
Posts: 124
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From: compton, ca.
yes they will block those two little holes i just installed a complete racing beat exhaust in my 79 threw in a sidedraft dellorto 48 and changed from points to electronic firing system i also custom made 8.5mm msd wires and 2 blaster 2 coils thats the way to treat a 79.
HEAVY METAL THUNDER
Joined: Oct 2002
Posts: 3,864
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From: Elsenborn, Belgian Eifel
Almost right Steve! We kept the 79 system right down to our S4 FC in Europe, so we're very familiar with it. The reason those small pipes run where they do is not heating the airpump air, but cooling the reactor and mid-silencer (by lack of a better name I'll call it like this) They actually don't need excess-fuel in the thermal reactor, but oxygen to burn the excess fuel that is there due to the design of a rotary engine.
That's also why it needs cooling: the inside of the reactor and mid-silencer could melt if not cooled.
That's also why it needs cooling: the inside of the reactor and mid-silencer could melt if not cooled.
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FB+FC=F-ME
Joined: Jul 2004
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From: Rohnert Park CA
Originally Posted by rotary emotions
Almost right Steve! We kept the 79 system right down to our S4 FC in Europe, so we're very familiar with it. The reason those small pipes run where they do is not heating the airpump air, but cooling the reactor and mid-silencer (by lack of a better name I'll call it like this) They actually don't need excess-fuel in the thermal reactor, but oxygen to burn the excess fuel that is there due to the design of a rotary engine.
That's also why it needs cooling: the inside of the reactor and mid-silencer could melt if not cooled.
That's also why it needs cooling: the inside of the reactor and mid-silencer could melt if not cooled.
According to my info,which comes directly from John Matras book,
"The trailing plugs switched off at part throttle to assure a rich mixture in the exhaust to keep the thermal reactor cooking and emissions low."
True,oxygen is needed to combust the waste products,but if there isnt enough fuel for the "fire",then there is no fire.
At full throttle and idle,all the plugs fire.
And,the heat exhanger is used to preheat the smog pump air before it enters the reactor because,"The heated air promoted combustion better than relatively cool air direct from the air pump."
A portion of the airpump air is used to cool the reactor,hence the double wall jacketing around the reactor.
Not trying to argue or start a pissing match,just relaying info direct from the source.I have found this book to be highly technical and accurate in the past....
Steve,
Your timing is impecable with the info on the SA exhaust. I have one in the shop now and had never worked with this style. The engine had very weak exhaust pressure, even with the cat dropped, now I know why. As a result, it gets headders.
Thank you very much for your usual detailed and insight posts.
Trochoid.
Your timing is impecable with the info on the SA exhaust. I have one in the shop now and had never worked with this style. The engine had very weak exhaust pressure, even with the cat dropped, now I know why. As a result, it gets headders.
Thank you very much for your usual detailed and insight posts.
Trochoid.
HEAVY METAL THUNDER
Joined: Oct 2002
Posts: 3,864
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From: Elsenborn, Belgian Eifel
Steve, I just rely on my info too, coming from what Mazda told their dealers back then. Don't really know who's right/wrong. It doesn't really matter either: headers are the way to go anyway! 
Hey Chris-
some more thoughts during the exhaust upgrade:
1) replace all the rubber exhaust hangers with new parts. Yours will be shot. I have the factory parts book and can snail-mail you a copy of the parts page with illustrations and part numbers. Mazda and/or mazdatrix should have all these.
2) likewise all the gaskets, though these will come with the exhaust system if you are buying a new one from RB/mazdatrix (same unit)
3) consider replacing the Tranny support pads (rubber) on the rear Tranny cross member. Easy access with the exhaust out
4) in my swap I bought all Stainless Steel attachment hardware (ie nuts and bolts). Other than heat-critical areas like the exhaust manifold (header) nuts, the SS parts will never rust and should not seize. Speaking of which, use Anti-Seize on the threads during assembly (Mazdatrix sells this) to guarantee easy removal down the road. This can include the header studs since anti-seize is highly heat resistant. For the SS hardware, be sure and take in samples of your existing hardware to be sure of thread pitch/compatibility
5) I pulled the Heat Shields down from mine after the exhaust was out. I had them sandblasted and powdercoated. Look like new (though you'll need a mirror to appreciate them
) and they will never rust. Same SS hardware treatment for these to
- and while the shileds are out, this is a great time to check for any rust issues and take care of those. Note especially around the muffler area where a good metal brushing and some POR 15 (por15.com) can do wonders. There WILL be rust!
6) remember you may need the INTERMEDIATE PIPE of your original exhaust! You can chop the secondary small pipe off if you like, you won't need it with the header set-up. Again, I took mine in and blasted and powdercoated it to prevent rust (on the OUT side) not sure what can be done INside it...
7) if you haven't removed the stock reactor yet you will find that a hinged(!) 14mm socket head is a Gawd-send in getting some of the reactor nuts off!! (uppers are buried up tight to the intake mainfold)
Best of Luck
Stu Aull
80GS
Alaska
some more thoughts during the exhaust upgrade:
1) replace all the rubber exhaust hangers with new parts. Yours will be shot. I have the factory parts book and can snail-mail you a copy of the parts page with illustrations and part numbers. Mazda and/or mazdatrix should have all these.
2) likewise all the gaskets, though these will come with the exhaust system if you are buying a new one from RB/mazdatrix (same unit)
3) consider replacing the Tranny support pads (rubber) on the rear Tranny cross member. Easy access with the exhaust out
4) in my swap I bought all Stainless Steel attachment hardware (ie nuts and bolts). Other than heat-critical areas like the exhaust manifold (header) nuts, the SS parts will never rust and should not seize. Speaking of which, use Anti-Seize on the threads during assembly (Mazdatrix sells this) to guarantee easy removal down the road. This can include the header studs since anti-seize is highly heat resistant. For the SS hardware, be sure and take in samples of your existing hardware to be sure of thread pitch/compatibility
5) I pulled the Heat Shields down from mine after the exhaust was out. I had them sandblasted and powdercoated. Look like new (though you'll need a mirror to appreciate them
) and they will never rust. Same SS hardware treatment for these to- and while the shileds are out, this is a great time to check for any rust issues and take care of those. Note especially around the muffler area where a good metal brushing and some POR 15 (por15.com) can do wonders. There WILL be rust!
6) remember you may need the INTERMEDIATE PIPE of your original exhaust! You can chop the secondary small pipe off if you like, you won't need it with the header set-up. Again, I took mine in and blasted and powdercoated it to prevent rust (on the OUT side) not sure what can be done INside it...
7) if you haven't removed the stock reactor yet you will find that a hinged(!) 14mm socket head is a Gawd-send in getting some of the reactor nuts off!! (uppers are buried up tight to the intake mainfold)
Best of Luck
Stu Aull
80GS
Alaska
Thread Starter
Joined: Mar 2005
Posts: 1,584
Likes: 1
From: Massachusetts
Originally Posted by 7aull
Hey Chris-
some more thoughts during the exhaust upgrade:
1) replace all the rubber exhaust hangers with new parts. Yours will be shot. I have the factory parts book and can snail-mail you a copy of the parts page with illustrations and part numbers. Mazda and/or mazdatrix should have all these.
2) likewise all the gaskets, though these will come with the exhaust system if you are buying a new one from RB/mazdatrix (same unit)
3) consider replacing the Tranny support pads (rubber) on the rear Tranny cross member. Easy access with the exhaust out
4) in my swap I bought all Stainless Steel attachment hardware (ie nuts and bolts). Other than heat-critical areas like the exhaust manifold (header) nuts, the SS parts will never rust and should not seize. Speaking of which, use Anti-Seize on the threads during assembly (Mazdatrix sells this) to guarantee easy removal down the road. This can include the header studs since anti-seize is highly heat resistant. For the SS hardware, be sure and take in samples of your existing hardware to be sure of thread pitch/compatibility
5) I pulled the Heat Shields down from mine after the exhaust was out. I had them sandblasted and powdercoated. Look like new (though you'll need a mirror to appreciate them ) and they will never rust. Same SS hardware treatment for these to
- and while the shileds are out, this is a great time to check for any rust issues and take care of those. Note especially around the muffler area where a good metal brushing and some POR 15 (por15.com) can do wonders. There WILL be rust!
6) remember you may need the INTERMEDIATE PIPE of your original exhaust! You can chop the secondary small pipe off if you like, you won't need it with the header set-up. Again, I took mine in and blasted and powdercoated it to prevent rust (on the OUT side) not sure what can be done INside it...
7) if you haven't removed the stock reactor yet you will find that a hinged(!) 14mm socket head is a Gawd-send in getting some of the reactor nuts off!! (uppers are buried up tight to the intake mainfold)
Best of Luck
Stu Aull
80GS
Alaska
some more thoughts during the exhaust upgrade:
1) replace all the rubber exhaust hangers with new parts. Yours will be shot. I have the factory parts book and can snail-mail you a copy of the parts page with illustrations and part numbers. Mazda and/or mazdatrix should have all these.
2) likewise all the gaskets, though these will come with the exhaust system if you are buying a new one from RB/mazdatrix (same unit)
3) consider replacing the Tranny support pads (rubber) on the rear Tranny cross member. Easy access with the exhaust out
4) in my swap I bought all Stainless Steel attachment hardware (ie nuts and bolts). Other than heat-critical areas like the exhaust manifold (header) nuts, the SS parts will never rust and should not seize. Speaking of which, use Anti-Seize on the threads during assembly (Mazdatrix sells this) to guarantee easy removal down the road. This can include the header studs since anti-seize is highly heat resistant. For the SS hardware, be sure and take in samples of your existing hardware to be sure of thread pitch/compatibility
5) I pulled the Heat Shields down from mine after the exhaust was out. I had them sandblasted and powdercoated. Look like new (though you'll need a mirror to appreciate them
) and they will never rust. Same SS hardware treatment for these to- and while the shileds are out, this is a great time to check for any rust issues and take care of those. Note especially around the muffler area where a good metal brushing and some POR 15 (por15.com) can do wonders. There WILL be rust!
6) remember you may need the INTERMEDIATE PIPE of your original exhaust! You can chop the secondary small pipe off if you like, you won't need it with the header set-up. Again, I took mine in and blasted and powdercoated it to prevent rust (on the OUT side) not sure what can be done INside it...
7) if you haven't removed the stock reactor yet you will find that a hinged(!) 14mm socket head is a Gawd-send in getting some of the reactor nuts off!! (uppers are buried up tight to the intake mainfold)
Best of Luck
Stu Aull
80GS
Alaska
1) I have a few of the rubber hangers from a few years ago so I can replace them.the hanger about halfway down the exhaust,and the rear one before the muffler were dry-rotted,and broke whan I was removing the exhaust.
2)I have the Racing beat exhaust already from my 83,and I have the gaskets already as well,but thanks for the heads-up.
3) I thought about replacing that bushing before I remived the tranny,but it look like it was in great shape so when I placed my order with Mazdatrix last tuesday I didn't order the mount.
4) A few years ago when I removed my Racing beat exhaust for a clutch swap on my 83 I quickly realized the bolts that came with the exhaust were not high quality,and I replaced them with stainless then,and I have used high temp copper never-sieze on them,and the exhaust studs on the engine since.I actually had 2 broken studs on the engine in my 83 at that same time so helicoils,and never-sieze are my friends.
5) The underside of this car is so clean I don't dare remove the heatshields,and such,as they are in great shape.
6) I am not sure about what you mean by the intermediate pipe,but I am using my whole Racing beat full dual exhaust so I don't need anything,as far as I can tell.
7) I wish you had replied sooner on this one,as I removed the intake manifold to get to those nuts on top,but it wasn't a big deal because I wanted to clean up the manifold anyway.
I am just waiting for parts now from Mazdatrix.They should be here by Tuesday.I plan to also upgrade to the electronic ignition as well,but my friend is driving me crazy about cutting the factory harness,and soldering in the wiring from my 83 to make this happen.I think it can be done a lot easier,and quicker,as well as easier to go back if I want in the future.
Do you guys think I am an a$$ for upgrading the ignition,and exhaust?I plan to keep all the factory stuff to keep this thing original as can be.I sort of want to upgrade to the 81+ brakes as well,but I am not sure it keeps the car true to its roots,so I may not.What are your thoughts?Thanks again
Chris
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