Adding cats to mid pipe?

[kerrit]

Given the $3k cost of the AMS catted downpipes, I was wondering if anyone has done catless downpipes and then added cats downstream?

Is there any room to weld on cats without hitting the underside of the car?

[Craze]

There is room

[1320racer]

kerrit: Great start to a thread! I have had these same thoughts and I am too currently investigating how far one can locate the cats downstream for them to be effective and safe.

I'm still reading (and I will test mine to see if this is true) but it seems more recent catalytic converters, when operating normally, are between 1200 F to 1600 F. But if there's a problem or a clog, they will become even hotter (2000 F).

Older, carbureted egnines often have exhaust temperatures in the 1100 F to 1300 F range with fuel system calibration for power enrichment typically designed into the carburetor.

Edit/Correction: (Click here) for resource
Depending on the application, catalyst inlet temperature is often 650 C to 850 C at the inlet to the first catalyst. It is typically controlled to a 850 C to 900 C maximum temperature, often by fuel enrichment in engines with PFI fuel systems. The limiting factor for exhaust temperatures in the past had largely been exhaust catalyst durability (sintering of active metals and metal oxides and washcoat/substrate durability). Catalysts have improved to the point that the limiting factors nowadays are often the exhaust valve, exhuast port, exhaust manifold and, if the application is boosted, turbocharger turbine housing materials. Catalyst bed-temperatures differ from inlet and outlet temperatures due to thermal mass after startup and due to exothermic reactions during warmed-up operation. I have unpublished exhaust temperature data that is more recent but here is a link to some older published powertrain development data that includes exhaust and catalyst temperature data that may be of interest:


When I installed 200 cell cats on my Jag, they were welded 5 inches downstream from stock to simplify the install (due to angle and curvature of the cats) and they worked fine since there was still a lot of stock heat shielding that far downstream. Beyond 8 inches, the heat shielding was insufficient and the connections for the sensors would not reach anyway. I did not want to buy, or make, sensor extensions.

[kerrit]

Originally Posted by 1320racer

kerrit: Great start to a thread! I have had these same thoughts and I am too currently investigating how far one can locate the cats downstream for them to be effective and safe.

I'm still reading...but it seems more recent catalytic converters, when operating normally, are between 1200-1650 F. But if there's a problem or a clog, they may become very hot (2000F).

Older, carbureted egnines often have exhaust temperatures in the 1100 F to 1300 F range with fuel system calibration for power enrichment typically designed into the carburetor.

Edit/Correction: (Click here)
Depending on the application, catalyst inlet temperature is often 650 C to 850 C at the inlet to the first catalyst. It is typically controlled to a 850 C to 900 C maximum temperature, often by fuel enrichment in engines with PFI fuel systems. The limiting factor for exhaust temperatures in the past had largely been exhaust catalyst durability (sintering of active metals and metal oxides and washcoat/substrate durability). Catalysts have improved to the point that the limiting factors nowadays are often the exhaust valve, exhuast port, exhaust manifold and, if the application is boosted, turbocharger turbine housing materials. Catalyst bed-temperatures differ from inlet and outlet temperatures due to thermal mass after startup and due to exothermic reactions during warmed-up operation. I have unpublished exhaust temperature data that is more recent but here is a link to some older published powertrain development data that includes exhaust and catalyst temperature data that may be of interest:



When I installed 200 cell cats on my Jag, they were welded 5 inches downstream from stock to simplify the install and they worked fine since there was still a lot of stock heat shielding that far downstream. Beyond 8 inches, the heat shielding was insufficient and the connections for the sensors would not reach anyway. I did not want to buy, or make, sensor extensions.

these are good considerations I didn't think of!

I deleted the primaries and ran the stock secondaries on my e90 M3 for a while, this was a common mod and they're located quite a bit further downstream - here's a pic of the stock pipe:



Really the goal here is to not have the fuel smell issues from going fully catless, which I deal with on my e90 but don't want to deal with it on my DD m5

[1320racer]

Thanks for including the picture. Is there an optical illusion or does the stock exhaust system go from ~2.5 inches to more than 3 inches at the rear exiting mufflers?

[F10CPROG]

Heatwrapping the downpipe upto the cats will help keep the exhaust temps up so cats can be located further back i would have thought?

[1320racer]

Originally Posted by F10CPROG

Heatwrapping the downpipe upto the cats will help keep the exhaust temps up so cats can be located further back i would have thought?

I have no experience wrapping downpipes (or anything) with heat tape but you bring up a good point that it should allow us to move the cats back even further. How far is still an unknown. I read an article (I will try to find and paste a hyperlink) where a tuned F10 M5 with 800+hp wrapped the turbos and decatted downpipes, which resulted in the under hood temps dropping ~200 degrees. I don't recall if that was C or F.