So the mechanic working on my 79 Sa says my thermal reactor is shot as its causing the car to run hotter than usual. He suggested I replace the system with the catalytic converters found on a 84 . Is this a good idea ? I have a guy who can sell me a used thermal reactor from a low mileage car but he wants near 600$ for it ( he is local, I have placed an add up on here ). The mechanic says he can get me a sub 200 price for a low miles cat . Opinions? I also stress the 7 is becoming my daily as my daily died on me.

 

Full RB exhaust only @$200.00 more than what is being asked for thermal reactor. I see you're in California,what are your emissions requirements,you're in the **** emissions state and may not be able to install a later FB exhaust legally. If inspection/emissions no issue,RB system most cost effective.

 

If I remember correctly, the later manifolds will bolt up but there are air injection ports in the housings that it doesn't cover. I'm sure you can find someone selling a thermal reactor for cheaper than $600. That absurd to ask that much for one. But then again, parts prices for these cars have gone up over the last few years.

 

it is actually not legal to put a catalytic converter on a car that never had them, even in California.

i should point out that a THERMAL reactor is supposed to be hot, that is how it works.

 

I've only had '85 FB's, so no personal experience with thermal reactors (only cast iron manifolds). I thought it was a cast manifold specially designed to get extra hot/oxygenated and work like a cat? Sort of. What can go wrong with them, besides the "cooling shell" or the air pump feeding it? Is that what we're talking about here... the outer shell rotting off and now the iron is getting too hot for safety?

 

The cast iron manifold IS the "thermal reactor". All FB's had them unless converted to straight headers.

I wouldn't worry too much about the thermal reactor getting too hot unless it's getting red hot or something strange. Your mechanic might be seeing the cat getting too hot if he's messing with the sensor that comes stock on them to let you know of an overheat...

 

Nope. The SA's (79-80) have a "thermal reactor" which is a different part than the big log manifolds we have on 81-85 fb's. It's bigger and designed to get really hot, like a CAT. The FB manifolds are just manifolds, with cats behind them.

I just don't know what can go wrong with them, other than the air pump system.

 

70-80 Thermal Reactor on left, 81-85 manifold on right. The manifold normally has a heat shield in it, but you can see they are different parts.

 

I recall that the thermal reactors (talking 79/80 here) have some internal passages or something that are prone to failure and then clogging, yatta yatta. Been a while since I looked at my old one and it's since been scrapped.

As far as I know you can install the later FB manifolds on a thermal reactor equipped engine block, however not the other way around (someone check me on that, it's been a while since I've seen one). As I saw someone mention above, there are extra ports on the earlier engines which work with the thermal reactor, and without these it will not function properly. I installed an FB exhaust and smog system (intake manifold, and rats nest included) to pass emissions originally. This worked for me because at some point before my ownership, a later year 12A was swapped in that did not support the thermal reactor (ports missing). I was able to pass smog with a FB exhaust manifold, mostly blown out cat, the air pump, and some rats nest tomfoolery but your mileage may vary, particularly if your car still has the correct engine.

My suggestions at this point would be to either...

1) source a new thermal reactor if that's been working for you so far
2) get an RB or custom exhaust if your emissions laws permit it (RB will be far simpler)
3) try to install some cats (if this is legal....? I did it). This could be:
- the system from an FB generation car, however the smog system of the SA will not really know what to do with the FB parts so you'll need to do a little finagling.
- a universal heavy metal cat (not high flow, those don't help you pass smog too well) and figure out some solution for a manifold. At one point I had an exhaust on my car where an FB manifold was welded to some pipe and then to a cat; not great long term, but it let me pass smog.
- a custom exhaust (maybe an RB header; the collected version will make this easier) with some form of universal cat like I mentioned in the previous option.

Getting a new thermal reactor will be the most straight-forward. I'm not too sure how the FB exhausts will bolt up, but they won't match the smog system so it will require some work regardless. At that point a custom cat setup might just be easier, although I can't say for certain. Most of this will depend on your smog laws.

That got a little convoluted but hopefully there's some useful info in there somewhere.

 

Well I stand corrected. I had no idea they were different.

 

Well, let's throw some science in here so we can gain a better understanding of the method;

The SA Thermal Reactor is huge and heavy. It has a port leading directly into it's front end which is fed by the Air Pump and the Air Control valve on the side of the manifold to control where air is directed. The Control Valve has a secondary exhaust pipe about 1.5" in diameter that leads all the way to the muffler - but most of your cars will be missing this, as it likely rusted out over time. Originally, this kept bypass air from the exhaust ports on the engine exiting behind the CAR when it could not be pumped into the Thermal Reactor. The heavy cast iron Reactor is designed to contain exhaust gas for an extended period of time, and the internal port baffles which are installed into the Reactor inlets when its installed are directional AGAINST the natural flow of air. This is why they erode quickly and rusty chunks get blown out the exhaust and captured in the muffler.

The Thermal Reactor lives up to its name in that it is designed to retain heat. The Air Pump supplies fresh oxygenated air to the Reactor so that the oxygen car react with unburned hydrocarbons to reduce HCO, oxides of nitrogen and create carbon dioxide instead of CO (carbon monoxide). The high heat environment is what fosters this chemical reaction, so Thermal Reactors run HOT. If they don't, they just function as manifolds. The primary benefit of a Thermal Reactor is that it's cheap to manufacture - it is not particularly effective, especially during warm-up - which is why later FB cars got better catalytic reactors.

For 81+ cars, the Catalytic Converter uses platinum mesh to store heat and the high chemical reactivity of platinum as a metal is what fosters the chemical reaction, instead of just high heat. Heat is needed, however - and expected, as shown by all of our cars having a Thermal probe on the passenger side of the tunnel and a corresponding idiot light on the dash to warn you of an impending fire! There are 3 catalysts on 81+ cars, two smaller monolithic converters (*which function much like mini Thermal Reactors, and the Main Catalytic Converter that needs fresh air to operate. That thin pipe coming from the Control Valve at the intake manifold and fed by the Air Pump is what supplies it.

Now you know!

 

These things are built like tanks, with no real moving parts. The original post states that the mechanic said "the thermal reactor is shot and causing the car to run hotter than usual" Would it really erode away to the point of being non-functioning (a hole internal or external somewhere) and would that make the engine run hotter? It doesn't add up to me.

 

The guy rebuilding my engine is eddyrenown . Legality is of no issue, I won't go any further on that topic though, let's just say all the emissions systems went bye bye , so I'm not concerned about the legality of my car at this point. Consider it a form of protest from a law student to the state who enacted an bonkers law forcing ga 40 year old car to pass modern-day smog laws, if people can burn down buildings, I can grease some palms. He said is it's making the 12A run hotter than it should as evident by the seals being flat ( no damage to the irons or anything else ) . Id swap to a RB set up but it's on backorder until mid-September and I need the car ASAP . If any of you guys could hook me up with a RB set, used or otherwise and are near LA CA , il buy it. Mind you I only have around 400$

 

An RX7 resto is no place for a starving artist.

 

I have seen a handful of thermal reactor manifolds degrade to point where they began to break up internally and the broken up pieces partially plug exhaust outlet. This condition can make engine run hotter as well as noticeably down on power. You can see damage with reactor removed and i have removed the broken pieces and reinstalled reactor for in transit customer to continue their trip and replaced reactor manifold when ordered part came in.

 

There is a RB header in Indiana for $60. It is a Facebook marketplace item 203837024118039

 

So the additional heat is due to the blocked exhaust. That makes some sense. Thanks.

 

i completely agree with this part, i am so tired of smogging cars, they always pass! you are missing the loophole though, if the reactor is NLA, and it makes you fail smog, they give you an exemption, although only for 2 years

or since it is not legal to put a converter in a car that didn't come with one, you can put an 81+ engine in there with no cat, and its perfectly legal...

 

California smog laws are just ridiculous if you ask me. Just wanted to add that.

 

In CA can you register the car as Classic or Antique and get away from emission check? That's what I did with mine (PA Classic plate).

 

I think in CA the cut off is 1975 and hasn't changed in years., Here in NC its 35 years old so its rolling.

 

In PA its 15 years or older to get "Classic" status and 25 or older for "Antique" status. Neither requires emissions check. But you have to request those tags from the state.

We also have a rolling 25 year no-sniffer check, but everything '74 and newer gets a visual check for OE emissions parts. Unless you have the Classic or Antique tags.

Fun fact for '96 and newer cars with OBDII port - as long as the computer doesn't show any codes, you pass emmissions. All the tuner cars are CAT-less, EGR-less, etc etc but as long as your tuner reprogrammed the computer for the mods, and the computer shows all-good, you pass emmissions.

 

you can register it that way, but i think it still needs a smog?

 

i'm ready to go to Nevada or Oregon for registration, its 10x cheaper, less hassle

 

Same here and no one really cares about visuals.