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I went ahead and bastardized my RMM dp 12 months ago with a hi-flo cat. About 2 weeks ago on cold startups there is a rattling noise coming from the passenger side and once the car is fully warmed up the noise completely dissappear.

Put the car up on stands and lightly tapped the DP with my fist and the damm cat was making the exact same rattling sound. Ask a muffler about the noise and they said that a "ceramic biscuit" could have broken inside the cat that is what is causing the rattling noise and once the car is fully warmed up it expands and stops making the noise. Called up the cat manufacturer and they confirmed that the "ceramic biscuit" could break if the car is running rich. They explained the a rich fuel mixture could easily elevate the temps. inside the
cat to above normal causing it to "burn up", weaking whatever is inside causing it to break.

Anyone with a hi-flo cat a year or older have any problems?

I currently don't have a fuel controller, which is probably my next mod.
 

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If you are using an inexpensive high flow cat I wouldn't be surprised. I don't know if a rich mixture would cause it to break loose, I would lean more toward cheap manufacturing/design.
 

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I did the same thing to my RMM and never use the hi flow cat (Random Technologies) . The cool thing is I had the muffler dude put flanges on my cat and DP so I can interchange the cat in and out when I want. It's great for passing emissions tests though. Cars that run rich like BPU cars will make quick work of catalytic converters. Ask Dennis Walsh or Anarkey (sp) on this forum for a reason why! :)

sleeper said:
I went ahead and bastardized my RMM dp 12 months ago with a hi-flo cat. About 2 weeks ago on cold startups there is a rattling noise coming from the passenger side and once the car is fully warmed up the noise completely dissappear.

Put the car up on stands and lightly tapped the DP with my fist and the damm cat was making the exact same rattling sound. Ask a muffler about the noise and they said that a "ceramic biscuit" could have broken inside the cat that is what is causing the rattling noise and once the car is fully warmed up it expands and stops making the noise. Called up the cat manufacturer and they confirmed that the "ceramic biscuit" could break if the car is running rich. They explained the a rich fuel mixture could easily elevate the temps. inside the
cat to above normal causing it to "burn up", weaking whatever is inside causing it to break.

Anyone with a hi-flo cat a year or older have any problems?

I currently don't have a fuel controller, which is probably my next mod.
 

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No problems here with my random tech high flo bullet cats. But my dad's '96 Bonneville had its cat replaced from rattling noises (broken segments in the cat). That car was stock of course., I did try experimenting with propylene oxide in the fuel during a magazine test, but that makes the mixture leaner (oxygen is contained in the propylene oxide and hence you carry oxygen in the fuel rails). Rich tuning, bad sensors, big injectors w/o compensation in programming can cause the cat to clog from overwork and maybe break off. Bad O2 sensors from runnig too much leaded race fuel can also cause rich running.
 
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