Cats for Classics?

Ransom said:

alfadriver said:

so back to the basics- O2 + fuel = combustion.  Without one of them, you won't have combustion- so lean, where there's almost no fuel is cooler, and rich where there's almost no O2 is cooler, too.  But in either case, if you give it fuel when lean or air when rich- you will get combustion in the catalyst.

In an attempt to keep the education and clarification thing going, I know I've associated lean with hot, but perhaps that's just all about slow combustion and heating exhaust valves?

And to make sure I understand your last sentence, you're talking about a misfire dumping unburned fuel into a lean environment in the catalyst, or a leak adding oxygen to a rich environment, either of these causing cat-destroying combustion?

Lean in of itself is not the hottest- as Paul_VR6 pointed out, the peak combustion and exhaust temps come right at stoich (or so very lean of stoich that you would not really notice).  I think the "lean = hot" is when you are trying to make the most power, and are running 11-12:1 for best power- and it goes lean from there- that will quickly elevate temps.  But the peak temp is always at stoich.

And the point of the last sentence is that there's enough fuel and air as a combination in the exhaust to support a significant exotherm in the catalyst- just pointing out a couple of ways you can get it other than a dead misfire or rich and an air pump.

amg_rx7 said:

I would definitely install one of the modern metal core 300 cell cats in an old car to clean up the nasty stench. You’ll definitely get some good life out of it 

I successfully used one in my FD RX7 running around 10.9-11.2 afr and premixed when on track for a good 5 years and about 35k miles and it was still functioning and not clogged when I removed it for a mid pipe with both a metal cat and muffler to quiet the car. 

Here is an example of what I used:

https://www.summitracing.com/parts/mpe-59959?seid=srese1&gclid=EAIaIQobChMIr6vMnuza5AIVdBh9Ch0r4gE7EAQYBCABEgKXgvD_BwE

 

FWIW, that may work, somewhat.  But it's not going to be super efficient.  There can't be much metal washcoat on that catalyst- not for $105.  Metallic catalyst substrate is considerably more expensive than an equal flow ceramic.  If it works good enough, it works, though.

alfadriver said:

amg_rx7 said:

I would definitely install one of the modern metal core 300 cell cats in an old car to clean up the nasty stench. You’ll definitely get some good life out of it 

I successfully used one in my FD RX7 running around 10.9-11.2 afr and premixed when on track for a good 5 years and about 35k miles and it was still functioning and not clogged when I removed it for a mid pipe with both a metal cat and muffler to quiet the car. 

Here is an example of what I used:

https://www.summitracing.com/parts/mpe-59959?seid=srese1&gclid=EAIaIQobChMIr6vMnuza5AIVdBh9Ch0r4gE7EAQYBCABEgKXgvD_BwE

 

FWIW, that may work, somewhat.  But it's not going to be super efficient.  There can't be much metal washcoat on that catalyst- not for $105.  Metallic catalyst substrate is considerably more expensive than an equal flow ceramic.  If it works good enough, it works, though.

Correct. You won’t pass your state’s emissions tests but the cat will cut down the stench to acceptable levels. As you can imagine, a rotary without a cat is a nauseating stench and a ‘dirty’ exhaust considering the premix and rich AFR.  This type of cat helped dramatically and was durable 

So we've kind of come full circle from "never work, don't waste your time" to "Yeah, it should help but may not last" with a good discussion in between. Good Stuff.

To refine my original question - do we still need an air pump for dilution on an old fat carb car, or do the newer catalysts accept a wide enough HC range to skip that component? From Alfa's description above, it sounds like an air pump would not be recommended.

In reply to Dashpot :

Honesty, the carb+air pump systems are not all that good.  Nor robust.

If you really want a catalyst, find an EFI system for your car.  

In reply to alfadriver :

Nope, no resonator.  These are the components:

... and the mid pipe is tucked into the frame under the transmission. The frame rails of a Spitfire are close together and the body tub sort of wraps around it with the driveshaft and exhaust running in between.

It can actually be a task sometimes to keep the exhaust from rattling against the frame.

In reply to Ian F :

Does that really run inside the frame rail??  Or under it?

But your predicament is pretty clear.  Still, EFI running more accurate will help, but I hesitate to suggest that you take a performance hit and not use headers....

In reply to alfadriver :

Yep. The center pipe runs mostly between the frame rails. A good thing since otherwise it would probably get ripped off the car. Even tucked up as it is, the exhaust is prone to getting smacked. 

The header is the OEM system in Europe (where the Spitfire was never saddled with the single carb intake).  As much as running a cat would be nice, it would be pointless to even install the new engine I have for the car if I saddled it with the US-market exhaust manifold. It really is that bad. 

In reply to Ian F :

Well, I'll keep my eye out for some possible ideas, but I don't think there's much out there that wil help....  Sorry, man.

I know this sounds kind of simple as compared to the deep discussion in this thread but also make sure your AIR pump works, people. Especially when it comes to stink.