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· Mack
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Based on my understanding, that's pretty much spot on. Ever wonder why headers and high flow cats cause check engine lights? It's because the high flow cats are not filtering out as much stuff as the stock cats and the secondary O2 sensors detect this and set a code.

A better argument might be that not all cars benefit a whole lot from a super free flowing converter, i.e. you need to be at or above a certain power level before it makes a huge difference.
 

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That article had some truth to it, 7 or 8 YEARS AGO. it was written in 2004, out of date now. 100, 200, and 300 cell count metalic substrate cats blew that all away. Yes, Virginia, metal core cats, like what Solo uses do flow more. What the truth from that article should talk about is the size of the inlet and outlets as being just as important core material. Our large cats would flow more if the inlet and outlet were larger. a larger cat has more holes per inch, more holes per inch, more flow.
 

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Whoever wrote that is completely ignorant and retarded :slap:
I would ask if you can find a high flow cat for any car that has the same substrate density as an OEM cat, yet flows better than the OEM converter. Or on the flip side, find a HFC with a less dense substrate that still filters the same percentage of harmful gases from the exhaust as the OEM unit.

I went to a workshop held by a well known motorsports company and they basically held the same opinion. Yes you can pick up more power by having high flow cats, but you aren't being sold a product that functions at the same level as a stock converter. You're essentially paying "more for less." This explains why high flow cats are not as expensive as OEM cats. However, the high flow simply means "less filtering." Perhaps a more accurate product name would be low filter catalytic converter, but of course that's bad marketing because it would likely sell less units since people would opt for no cats instead of high flow cats.

You could also make the argument that people would still pay for high flow cats since some filtering and less crappy exhaust smell is better than no converters at all. It's a matter of personal preference at that point though.
 

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Time for a question like this.

How much does the inlet/outlet size affect the flow?

Does anything think LTs with hi flow cats could pass an actually emission's sniffer test? (ie.. not the standard OBDII scan check for codes that can be beat by turning off the rear 02s)
 

· Premium Member
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The owner of an exhaust shop once gave me the whole "there is no such thing as a high flow cat" line a few years ago. He may have read this article but the way he made it sound I took it that he meant no one cats flows better than the other, which is obviously not true.
 

· Arrival
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I am sure any straight through flowing cat with larger inlets/outlets will flow better than our large bodied, small inlet with a horrible 90 degree outlet stockers. Just sayin.
 

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A high flow cat is just that. High flowing. It does that by having less material. Sure it doesn't run as clean as an oem but it doesn't mean that it isn't converting... You could still pass the sniffer test with high flow cats, plus have a faster car with more power. That is indeed fact.
 

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Yeti, that's encouraging especially since you live in Ca. That passing grade might mean a Pat G custom "emissions tune" though?
I have several friends with cammed Ls1 And ls2 Gto's that have passed the sniffer with hfc's.

When pat g spec'd my cam he did it under the premise that I needed to pass smog. I have run the car with and without solo hfc with my cam and the solo cats eliminate all that stank smell the car has when catless. Even though they are 200 cell they worked great and I am sure would have passed the sniffer. People have run them with out tunes and didn't throw a cel so...
 

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Based on my understanding, that's pretty much spot on. Ever wonder why headers and high flow cats cause check engine lights?
I drove around for two weeks after installing headers / HFCs before getting tuned. No lights, no codes. Car passes inspection 100%.
 

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Interesting article...in the first paragraph they say the product doesn't exist and in the next they define it...

The smell from the highflow cats is my biggest gripe about the car. Does anyone else think there catted header car is fumey? I'm curious how much doping or plating is on the Kooks cats compared to Solo or Random Technology products. My issue doesn't appear to be tune related because I had both Vector and PatrickG try and address it without success.

FWIW I had a cammed LS1 before this that had headers with the Random Technolgy cats and it wasn't nearly as fumey as the G8. Maybe my Kooks cats missed the plating operation? I don't think the header manufacturers have much incentive to sell cats with alot of plating because of its cost and do so more for the visual appearance.
 

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I would ask if you can find a high flow cat for any car that has the same substrate density as an OEM cat, yet flows better than the OEM converter. Or on the flip side, find a HFC with a less dense substrate that still filters the same percentage of harmful gases from the exhaust as the OEM unit.

I went to a workshop held by a well known motorsports company and they basically held the same opinion. Yes you can pick up more power by having high flow cats, but you aren't being sold a product that functions at the same level as a stock converter. You're essentially paying "more for less." This explains why high flow cats are not as expensive as OEM cats. However, the high flow simply means "less filtering." Perhaps a more accurate product name would be low filter catalytic converter, but of course that's bad marketing because it would likely sell less units since people would opt for no cats instead of high flow cats.

You could also make the argument that people would still pay for high flow cats since some filtering and less crappy exhaust smell is better than no converters at all. It's a matter of personal preference at that point though.
Just like air filters. More flow = less filtration.
 

· Car RamRod
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I am sure any straight through flowing cat with larger inlets/outlets will flow better than our large bodied, small inlet with a horrible 90 degree outlet stockers. Just sayin.
this. and yep, if you ditch the stock cats with the horrible 90 degree bend you will pick up hp...just ask anyone with midlength headers and HFC
 

· Arrival
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I have yet to get the "stank" smell since I ditching my cats... just sayin
Downshift in manual mode a couple gears when stopping at an intersection with your windows down. That is about the only time i ever smell the exhaust. Doesn't bother me, though.
 

· CCG8 / FLG8
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HF cats throw a code, usualy for failing the cat efficiency test. This is a test run by the ECM that alters the mixture briefly then looks at how long it take for the rear sensor to shown the change. HFC flow faster so the sensor responds too soon. Solo HFC come with rear sensor extenders. These add length (time) to the path of the gasses that reach the rear O2 and the ECM thinks all is fine.

Kooks make some "Green HFC" that they claim make the same power as their non-green hfc, don't throw codes and will pass sniff tests.
 

· HPT Pro Tuner
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I have yet to get the "stank" smell since I ditching my cats... just sayin
I take you have ditched the stock cats and the car is running catless. Give it a couple of days for your nose to catch up. She will stink :)
I love the smell though, but sometimes i wish it wasn't intense, usually when the popo is besides or behind the car at a stopligth. So far knocking on wood....


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