[DrBrutal]

Ok... So I've decided to throw a cat on the catless DP. One thing though, what cats are truly "high flow"? I can't imagine a cheap ebay "race" cat is actually any good.. Who knows what's what? I don't want opinions... I've seen 100 cell cats, which say "won't pass emissions" but I'm under the impression they aren't actually cats, but foolers.. Here's an example. It says "metallic core" where normal cats are ceramic.. What's the difference? Are these legitimate working cats? Like 90% of all ebay posts, there's no real -important- useful information on the product being sold...

http://www.ebay.com/itm/Catalytic-C...Parts_Accessories&hash=item3cbd35c32a&vxp=mtr

 

[bpray9223]

Magnaflow 59959

/thread.

 

[dave_n_ruth]

Cats float if you put them in a potato sack and throw them into a river. -Total myth!

 

[BMac_R]

Honestly, toss in the Magnaflow. It's unrestrictive and it saves you from headaches because the fumes will be somewhat filtered.

 

[DrBrutal]

Magnaflow 59959

/thread.

Is it actually more flow than stock? Seriously, the stock one is much wider, therefore, in theory it should have more flow. If stock and magnaflow have same CPSI (cells per square inch, which I do NOT know if they do or not), and the stock has a larger overall inner volume to length, then it would flow more, even with a smaller entrance and exit diameter.

However, it also has to be considered the overall length, and the amount of restriction per inch.. So... What's a good way to physically test which has more flow?

 

[unboxy-R]

All I know is I installed a set of BBK cats in a mustang that were "Hi-Flow" and in two years they wouldnt pass a sniff test in Virginia. The tech at the shop told the "Hi-flow" cats use less material in the cat to gain the flow, so they dont burn off the excess HC causing them to fail the test sooner.

 

[DrBrutal]

All I know is I installed a set of BBK cats in a mustang that were "Hi-Flow" and in two years they wouldnt pass a sniff test in Virginia. The tech at the shop told the "Hi-flow" cats use less material in the cat to gain the flow, so they dont burn off the excess HC causing them to fail the test sooner.

HC?

 

[BMac_R]

All I know is I installed a set of BBK cats in a mustang that were "Hi-Flow" and in two years they wouldnt pass a sniff test in Virginia. The tech at the shop told the "Hi-flow" cats use less material in the cat to gain the flow, so they dont burn off the excess HC causing them to fail the test sooner.

Magnaflow cats are 49 state legal and should pass the sniffer...mine did...if not then ummm use 2.

 

[1maitai]

HC?

hc = hydrocarbon. un-burnt fuel.

 

[DrBrutal]

hc = hydrocarbon. un-burnt fuel.

Damn. and I got an A in chemistry lol

still nobody has answered any of my important questions.

 

[spinall4]

In order to get real good quality legit cats that will take the punishment of a turbo car you will spend a lot of money. Eight hundred dollars or so.

You want metal core, ss body 304 some of the cheaper units are 409 ss, ect. The 100 CPI units may not make the second o2 sensor happy and a cel off. The trade off is less cells per inch flow better, but work less.

I have heard good things about this brand. Hjs is what awe tuning uses. If you search they had a good write up on why these are good

http://www.quality-tuning.com/catalytic-converters/p90950082.html

 

[thegrapist]

Is it actually more flow than stock? Seriously, the stock one is much wider, therefore, in theory it should have more flow. If stock and magnaflow have same CPSI (cells per square inch, which I do NOT know if they do or not), and the stock has a larger overall inner volume to length, then it would flow more, even with a smaller entrance and exit diameter.

You're not thinking about things in terms of fluid dynamics. Air, which flows exactly like fluid, flows best in a laminar (straight) pattern. When you have a pipe that expands then contracts you get turbulence. Turbulence is caused by the changes in high and low pressure zones. All things being equal, a straight pipe in most situations will flow better than something with a pipe that transitions to a larger diameter then goes down to a smaller diameter.

cliff notes: it flows like crap because the air expands inside the pipe then has to be packed into a smaller diameter

Do we know for sure if it flows better? No way. But based on that theory it shouldn't.

Also, I forget where I read this (maybe it was from FM), but a car actually lost power when the cat was removed. I guess the theory was that it aided the air in creating a laminar flow. Go on youtube and check out laminar flow hoses. It'll blow your mind.

 

[thegrapist]

The 100 CPI units may not make the second o2 sensor happy and a cel off.

True, but depending on the state this may not matter. In jersey if your car passes an obd2 scan, they don't do a tail pipe sniffer. So if your state is similar, one could *in theory* (and this is a hypothetical situation, purely for the sake of argument) just pop in an o2 spacer found on ebay and call it a day.

 

[SleepR_again]

Almost passed in MA the other day w/o cat whatsoever. No problem with the cat, just got nailed for not having the front plate. Now instead of a "5" on my windshield, I have an "R". Looks good.

 

[DrBrutal]

True, but depending on the state this may not matter. In jersey if your car passes an obd2 scan, they don't do a tail pipe sniffer. So if your state is similar, one could *in theory* (and this is a hypothetical situation, purely for the sake of argument) just pop in an o2 spacer found on ebay and call it a day.

I was running an o2 spacer on the OBX, however since it's a 45 degree angled bung, you can't get a 90 degree spacer on it, and a straight spacer + sensor makes the overall width too large, and it hits the firewall... It's only a matter of time before the sensor wires break off... Luckily, until this point, the OBX actually didn't fit properly, allowing for the spacer + sensor to fit without rubbing... Except it was rubbing on the other side of the exhaust well.

I do not have to pass emissions.. It's not required where my car is registered... So I will never have to pass any inspection... The only reason I want a cat is to get those damn fumes from pouring into my car. Nobody will ride in my car since the fumes are unbearable.

This is why I'm making this thread, I want to know the best cost-effective solution... I'll get one of those metallic 100-cell cats if I won't throw a code (just can't stand having a CEL) and if the fumes will go away, or be way less extreme. If the 100-cell will throw a code indefinitely (especially within a short amount of time) I'll pass. I'll get a cheapy magnaflow.

Just looking for solid, backed-up answers... Thank you to those who have given some.

So with all this being said, I'll leave it up to a vote, what would be my best option?

 

[DrBrutal]

You're not thinking about things in terms of fluid dynamics. Air, which flows exactly like fluid, flows best in a laminar (straight) pattern. When you have a pipe that expands then contracts you get turbulence. Turbulence is caused by the changes in high and low pressure zones. All things being equal, a straight pipe in most situations will flow better than something with a pipe that transitions to a larger diameter then goes down to a smaller diameter.

cliff notes: it flows like crap because the air expands inside the pipe then has to be packed into a smaller diameter

Do we know for sure if it flows better? No way. But based on that theory it shouldn't.

Also, I forget where I read this (maybe it was from FM), but a car actually lost power when the cat was removed. I guess the theory was that it aided the air in creating a laminar flow. Go on youtube and check out laminar flow hoses. It'll blow your mind.

This pokes holes in everything you said, sorta.. I'm not really finding videos that prove laminar flows better than turbulent. Except logically it makes sense.. Heat distribution doesn't necessarily mean better flow, though. The video doesn't really give a good argument to which is better.

 

[BeerEngineer]

You're not thinking about things in terms of fluid dynamics. Air, which flows exactly like fluid, flows best in a laminar (straight) pattern. When you have a pipe that expands then contracts you get turbulence. Turbulence is caused by the changes in high and low pressure zones. All things being equal, a straight pipe in most situations will flow better than something with a pipe that transitions to a larger diameter then goes down to a smaller diameter.

cliff notes: it flows like crap because the air expands inside the pipe then has to be packed into a smaller diameter

Do we know for sure if it flows better? No way. But based on that theory it shouldn't.

Also, I forget where I read this (maybe it was from FM), but a car actually lost power when the cat was removed. I guess the theory was that it aided the air in creating a laminar flow. Go on youtube and check out laminar flow hoses. It'll blow your mind.

This pokes holes in everything you said, sorta.. I'm not really finding videos that prove laminar flows better than turbulent. Except logically it makes sense.. Heat distribution doesn't necessarily mean better flow, though. The video doesn't really give a good argument to which is better.

I think it's that more bends/expansion/pressure changes slow things down, not whether it's actually laminar or turbulent. Laminar is a correlation, not a cause.

That said, if things cool more quickly, you will have more volume in a smaller chamber, moving slower, so that has to be weighed.

The car that lost power is probably an old NA, with poor fuel management, since they actually need a certain amount of backpressure to work properly. Not true in forced induction.

 

[bimmerd00d]

 

[BMac_R]

That is the most epic troll ever.

 

[dave_n_ruth]

That is awesome, lol.