Adding convertor (s). Yes, I said adding.

[SquareRoot]

Well ****! The Magnaflo rep tells me that the convertor must reach a minimum of 350 degrees to "light off".

My K20 has long tube headers and true dual 2.25" pipes. After crawling under it tonight, I realized there is no way on Gods green Corona virus infested earth that a cat is going to fit before the cross member.

Soo, I brought home a thermal temp gun from work and measured the pipes temp from the exhaust ports all the way to the rear axle.

Using long tube headers, the cat would have to essentially be connected to the header flange. It barely reached 350 degrees at that point. At the cross member where I have plenty of room, it barely got to 150.

I drove the truck and got the engine to temp (195) and let it idle during all the testing.

Just to be sure the readings were accurate, I took measurements with the temp probe on my Fluke multimeter. Same....

So I guess I'm **** out of luck. I'll have to rely on tuning the efi to get it the best I can.

 

[roundhouse]

Well ****! The Magnaflo rep tells me that the convertor must reach a minimum of 350 degrees to "light off".

My K20 has long tube headers and true dual 2.25" pipes. After crawling under it tonight, I realized there is no way on Gods green Corona virus infested earth that a cat is going to fit before the cross member.

Soo, I brought home a thermal temp gun from work and measured the pipes temp from the exhaust ports all the way to the rear axle.

Using long tube headers, the cat would have to essentially be connected to the header flange. It barely reached 350 degrees at that point. At the cross member where I have plenty of room, it barely got to 150.

I drove the truck and got the engine to temp (195) and let it idle during all the testing.

Just to be sure the readings were accurate, I took measurements with the temp probe on my Fluke multimeter. Same....

So I guess I'm **** out of luck. I'll have to rely on tuning the efi to get it the best I can.

You could use some short tube headers

 

[Frankenchevy]

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[SquareRoot]

You could use some short tube headers

Ummm......ok

You must be registered for see images attach

 

[SirRobyn0]

I'm no emissions expert here, but will cats have a shorter life if the A/F ratio is overly rich due to not having feedback from an O2 sensor? Then again, I don't think the auto manufacturers had any feedback when they started using cats back in the mid-1970s. The idea was to convert as much NOx and CO as possible to nitrogen, oxygen, carbon dioxide, and water.

***Edit: I just noticed the OP has EFI. But my question above is still a good one for a carburetor-equipped engine.

The short answer is yes, cats will have a short life the with a richer mixture, but there were plenty of carbed vehicles built without feedback systems including the one I drive, that have cat (s). A properly tuned carb will go a long way to mitigate that.

I am simply choosing by pipe size.
I haven't look much farther than that when I am browsing the selections.

Well ****! The Magnaflo rep tells me that the convertor must reach a minimum of 350 degrees to "light off".

So I guess I'm **** out of luck. I'll have to rely on tuning the efi to get it the best I can.

I can't tell you for sure that you'll get the cats to 350F everytime you drive it, but the reaction inside the cats does cause heat. In other words if you put a pair of cats in they will run hotter than the exhaust pipe temps you are reading right now. I can tell you on my truck with single exhaust, there is no way the pipe before the cat is 350F on most days, but I can tell you the cat is working. Most modern cars do have the primary cats on the manifold, but that is mainly so they warm up faster and start working quicker. I would put them on and not worry to much about temps, just get them as close to the front as you can. However changing to the short headers would be better.

 

[Rickf]

Would ceramic coated or wrapped headers push the heat towards the long tube collectors?

 

[CorvairGeek]

While none of them like a rich mixture, the 3 way catalyst (containing platinum, palladium, and rhodium) for control of HC / CO / NOx is dependent on a feedback fuel system (O2 sensor) for most efficient operation. The older design (2 way) for only HC and CO, not so much.

Did you know it is technically illegal (federal) to add a catalyst to a vehicle that didn't have one new, or add a second for true dual exhaust? You can thank the wizards of smart for the same reason that a used converter (which may be perfectly fine, lots of newer vehicles get totaled) cannot be legally resold. It can't be 'certified' that it is compliant.

 

[metal tech]

YES, long tube headers are going to need either ceramic coating or wrapped to keep heat in to light cat. This is also why most have to use a heated O2 sensor with headers, lack of heat. If you have the space put the cats right after the collector adapter. Trying to be green isn't easy on old stuff.