Question about Magnaflow High Flow cat on otherwise stock truck

[sneakingfart]

Hi everyone,

I have a '99 Suburban that I got for free in non-running condition. Fixed all of the mechanical issues and cosmetic issues, and part of that involved getting new catalytic converters. I went with a Walker cat that seemed decent. Anyway, about 6 months later, one of the cats is rattling inside (not heat shield), and truck sounds like a POS. Runs fine otherwise, I just can't stand the rattle. So I need to replace the cats again. Annoying, but is what it is. My question is, is there is significant performance benefit (or longevity benefit) to going with the Magnaflow high flow cats? It's about double the price, but I will go for it if you guys tell me it's worth it. My only experience with high flow cats is my 400 HP Civic Type R with a full 3 inch turbo-back exhaust and high flow cats, and it is so loud inside when accelerating that I would actually not be happy if it was my daily driver. Those of you that are running it, anything annoying about it? Noise, vibration, etc? This is my daily driver, and sometimes for the family when we need something larger and I don't feel like putting miles on my other cars. Thanks for your advice.

 

[df2x4]

I'm on my second Magnaflow Y-pipe/cat assembly on my red truck ('97 C1500 4.3L), and both have failed in the exact manner you describe. I'm just dealing with it for the moment on the second one. Granted this is on a V6 truck with a single cat so the 5.7L dual cat Magnaflow assemblies may be better, but I have not been impressed with part number 23457.

If and when I replace it again I'm thinking of trying the Flowmaster equivalent.

 

[Schurkey]

Make sure the catalyst is not overheating (likely due to misfire or failed O2 sensors.)

 

[sneakingfart]

I'm on my second Magnaflow Y-pipe/cat assembly on my red truck ('97 C1500 4.3L), and both have failed in the exact manner you describe. I'm just dealing with it for the moment on the second one. Granted this is on a V6 truck with a single cat so the 5.7L dual cat Magnaflow assemblies may be better, but I have not been impressed with part number 23457.

If and when I replace it again I'm thinking of trying the Flowmaster equivalent.

Hmm, that's unfortunate. I don't want to spend $850 just to have the same problem again. It seems to have a 5 year warranty, but still. Thanks.

 

[sneakingfart]

Make sure the catalyst is not overheating (likely due to misfire or failed O2 sensors.)

Thanks, I think it's unlikely. No misfire codes (no codes at all actually), and all 4 O2 sensors were replaced when I did the cats the first time. Truck runs and drives fine. Is there another way to check for misfires? I have an advanced diagnostic tool.

 

[b454rat]

Where in NY are you? I have the stock cats I took off my 99 Yukon.

 

[someotherguy]

IMO no benefit to the high flow on a stock application.

A while back one of the stock cats went bad on my '06 SS, rattling like crazy and finally blew into chunks so the exhaust sounded really dumb with one cat and one blown. Local performance exhaust shop welded in a universal fit Magnaflow for about $150. Can't beat that when the "direct fit" stuff is almost $800.

Richard

 

[Das Hatt]

New York State passed a law within the last year that any replacement cats has to either be OEM or have a CARB EO number. I live in New York also and Summit won't even ship a universal federal emissions cat to my house.

https://www.dec.ny.gov/docs/air_pdf/amccguide.pdf

 

[Supercharged111]

If the high flow version comes with a 2.5" head pipe and the non-high flow has the weak @$s 1 7/8" head pipe then yes, it's worth it even on a bone stock application. Is there a difference in head pipe sizes here?

 

[b454rat]

Must live in a populated area. They don't give 2 ***** where I am. Long as check on light isn't on, it's good.