BBK catalytic convers for shorty headers done


Active Member
Apr 3, 2015
So a few years ago 2015 I bought a BBK high flow x pipe with cats for my 93 Fox mustang LX for emissions. I installed cats when emissions test was required but cats were removed after I passed emissions which was usually 1 day tops.
Well this year was a bit different installed cats took to emission station and failed not because of cats something else ended up registering car in non emission county. But cats have been on now for a month but noticed last week again passenger cat is knocking or making noise. At first I though it was A I R Pump replaced under warranty and still noise coming from cat. A few days ago I confirmed it was passenger side cat got under car and could hear noise coming from cat,
But question is this is second set of BBK high flow cats I have burned up, I know they are ceramic inside which is not best material but second set of pipes I have messed up.
Is anyone else out there having same issue as I am having with these BBK high flow cats?
And anyone out there having better luck with another company and high flow cats?


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Active Member
Jul 12, 2018
I’ve come across quite a few BBK & other brands of single stage Catalytic Converters running cheaper monolithic “honeycomb” ceramic’s & avoiding usage of reinforcing with platinum & palladium, thus- easier to disintegrate. More economic as they limit/avoid more expensive elements, such as platinum, palladium, and rhodium, gold.
You get what you pay for..if even that. Late stage failure yields disseminated chunks. These types of Cat’s are made cheaply, a weak link, sensitive to to slight anomalies.
But, there’s another (?). Your Car has a small, undetected issue, it should be able to run these without incident, and for much longer periods..I’ve seen them run for 60K with no breakdowns, issues with Inspection.
I’m not a Treehugger, honest opinion is spending $$ once & installing high quality Cat’s, period. Motor is designed for this proximal back Pressure, and you won’t lose HP/TQ of any significance, power loss of concern due to running good Cat’s is A Myth.
An AIR (Smog Pump) has a very light parasitic loss, again- not significant.
Pypes , SLP both makes some good, solid Cats, as well as Kooks. Magnaflow’s top end Cat’s I also recommend. all offer Warranties. I’ve personally run each one listed. Flow is great, and they do a good job scrubbing the air. My 350HP 96’Cobra, 410HP 2008 GT, >700RWHP 2008 GT500 all run H or X pipes with Kooks Cat’s. I live in Mass., never had an emissions failure or issue with them.
There’s (5) general reasons Cat’s like BBK’s fail.
1) Physical impact. More Fragile.
2) Excessive combustion temperatures, thermal shock. Material bit more brittle.
3) Unburned fuel entering the Cat., breaking up the media, saturating & igniting.
4) Another element being burned during combustion, e.g., Coolant..
5) Obstruction within downstream exhaust.
6) Detonation. May be very subtle.
Details of above, alternative causes:
These generally won’t much affect high quality Cat’s, but larger issues may.
A) Most often cause is a result of unburned fuel entering Cat’s from improper air/fuel mixture (Generally rich, yet running too lean creates thermal spikes). Or a systematic issue, such as Leaky injector(s). Combustion occurs within Cat. Check Oil for fuel.
B) Intermittently firing cylinder(s), Ignition, weak spark or other ignition anomaly.
C) Aggressive ignition timing curve causing elevated Cylinder combustion temp’s, cheap ceramics cannot handle this well. Dieseling May occur in severe cases.(Tuning).
D) Leaky intake or head gaskets allowing coolant to enter during combustion.
E) Small leaks in upstream exhaust allowing cool 02/C02 causing thermal shock, cracking the composite. (manifolds/headers, etc).
F) Incorrect valve lash settings, I.E.; Valves adjusted tight, hanging open very slightly during combustion & escaping into exhaust.**
G) Poor quality fuels, inadequate Octane for Timing, Compression ratio.

** (F) Above not exclusive to, but more often in pedestal mount Rocker setups. I’ve had more than a few 302’s/351’s with 150lbs of Cyl.compression jumping to 180-185lbs with addition of shims, correcting excessive preload adjustment..
These engines generally ran decent, valve/valves affected were hanging open very slight, yet allowing fuel/superheated combustion gases to escape, creating thermal cracking of certain Ceramic Cat’s.
One “pop” & disintegration begins.
Hope this helps you, please feel free to ask any other questions. I’m not a Catalytic Converters expert, but have seen & dealt with many scenarios affecting them.
Good luck!
- John