This question is for all 2.0, 2.2, and 2.4 owners...

I just got a hi flow cat for christmas and I see it has an 02 sensor bung in it...

are you guys moving the secondary 02 sensor to this spot or leaving it in its stock location and covering up the spot on the cat?

 

oh btw, this is a Magnaflow Car Sound cat, 2.5" diameter

 

Well I have no cat at all, and left the o2 sensor where it would normally go, and I havent gotten a CEL

 

hmm, well I got this cat because I hear its one of the few that doesn't actually throw a CEL, just wondered if it had to do with the 02 sensor placement.

 

I dont think the engine will throw a CEL any way you put it, because if it doesnt throw a CEL without a cat at all, I doubt it will with a cat

 

thats possible but even some guys that have hi flow cats have thrown CELs...it could vary from car to car.

right now mine is throwing a CEL for my cat and I still have the stock one on so...I wanna make sure it goes away with a new cat.

 

I would just try putting it in there and if you get a code you will have to move it down. I would think it wont throw a cel. Thats the cat Im gonna get when I make my own downpipe this spring. Are you making a down pipe with that. If not you should because the stocker sux!

 

yeah I'll give it a shot, I should be able to have it welded in next weekend

 

hmm...kinda the wrong place to ask, but since its a yes or no question and its on topic, i might as well

would a hi-flow cat pass emissions in cali?

 

Put the cat on where the old one is. Use your second o2 sensor in that bung that's on the cat, and then after that use a 45 degree mendral bend and flange to mate up with the exhaust. That is what I did, but I have a vibrant cat without the bung. You'll end up with a nice full 2.5" downpipe then.

 

I suggest you put the CAT back on...cause when you go to have it inspected they are gonna use a sniffer on your car and your not going to pass inspection. Your also breaking federal laws by doing that too.

 

gotcha...I am already missing that flange after the cat...I already have full 2.5" exhaust from the header back. only thing left is the stock cat, which is now bad so its getting replaced with the magnaflow.

the reason I asked my question is because the stock secondary 02 sensor sits a little farther back, but I think I will move it.

oh and to answer your question hunterkiller, according to my box...this cat meets CARB
http://www.gravanatuning.com/applica...50_Hi_Flow_Cat

 

Inspection on all relatively modern cars is completly done through the computer.

 

All catalytic convertor modifications are illegal. That includes replacing your stock cat with a high flow catalytic convertor.

You wanna hear the really funny thing. Backpressure probe put in stock front O2 sensor location with stock cat convertor = .6psi backpressure. Same car, same exhaust, with magnaflow catalytic convertor = 1.1psi.

Every car since 2000 has come equipted with a high flow cat. Thats why the industry standard for exhaust system backpressure dropped from 2.0psi to 1.0psi.

Ill get the article and section that covers cat convertor replacement as soon as I get back to school.

 

Not necessarily true. If the cat converter fails, like almost everyone's on here has, you can replace it with a high flow cat that meets CARB standards. Not all states have emissions testing either. For instance, my car is registered in New Hampshire and they require a smog test where they hook up to my OBD2 port and let the car idle for a minute. I'm stationed in South Carolina however, where the car doesn't even have to be inspected at all!

 

You hit it on the head, any cat mods are against federal DOT laws. Only time a cat is permitted to be replaced is if the OEM cat failed. And yes, pretty much all cats made now are "high flow" cats. As for the sensor placement, the closer to the cat the better as far as a secondary o2 goes. I wouldn't run a primary o2 that close to the cat though, it will throw readings off that are required for fueling calcs.

 

okay, if hi flow cats are an industry standard, then why would a company sell hi flow cats...since theyd only be for replacements?

im just tryin to solve this cuz ive got one of those rare cobalts with a SAI and 2 cats, n thats gotta be robbin some horses

 

Because most people are uneducated about catalytic convertors. So if they can still be sold why not sell them. Not to mention they are still an upgrade for older model cars (1G dsm's, older honda, anything pre 1999 really).

Also, despite popular belief, a certain amount of back pressure is needed in an exhaust system. It allows for resonance wave tuning. Excessive backpressure is what is bad.

I cant believe they needed two cats and SAI. Wow. I havent had the chance to work on one of cobalts equipted like this but I wonder what the reasoning behind it is.

Truthfully any tampering with the cat is a federal offense and im not kidding when i say the first offense is good for up to 7 years in jail and a 10,000 fine PER cat convertor.

 

i cant imagine backpressure is good at all, even a little bit...exhaust velocity...sure...if pipings too wide, it would be hard for the exhaust to build its velocity, thus smaller pipes are needed (which is where i thought the whole "back pressure" thing came from)

according to the site, its legal in 49 states, and is only to be used in california if off-roading.
thanx though, glad someone responded

ahh yeah, about modding them...theres this

 

Theres a lot more to that then just 5 years 50k miles. Like i said, I can get the article and section number if you want to read all about cat replacement. I go back to school on the 2nd of Jan so if you want just PM me and Ill shoot all the information over to you. It is however very legal and long winded. Good stuff to know though.

You are correct. You dont neccesarily want ANY backpressure. However, true race exhausts have to be designed for a certain RPM range. The length and diameter of the pipe determine the RPM range the wave tuning works at. When the exhaust pulse reaches the collector, it changes velocity. It also creates a negative pressure wave that travels back through the header and creates a negative pressure area in the header. The idea behind TRI-Y headers is to create the higest negative pressure area in the tube for the cylinder that is going to open the exhaust valve next in the cycle. On a traditional small block chevy (with a 1-8-4-3-6-5-7-2), cylinder 4 is on the exhaust stroke after cylinder 8. So the negative pressure wave from cylinder 8 should create the greatest negative pressure in the exhaust tube for cylinder 4.

Above or below that rpm range, and you get backpressure. Its almost impossible to avoid. Just to give you an idea, this is the formula we use for building headers. It perfectly shows how rpm factors into exhaust design.
(850(180+EVO))
------------------- -3 = Header pipe length
Max Power RPM

EVO is exhaust valve opening at .050" lift at the valve.

 

I "thought" my OEM cat had failed so i replaced it with a magnaflow hi-flow. I wonder if thats breaking the law?

Either way, it DID throw a code but it DID NOT trigger a CEL. During some warranty work my dealership actually got a "reduced cat efficiency" code of somesort. But then again my car is a factory freaking hitting 22 lbs of boost with a stage 2 pulley.

Is the hi-flow worth the 80 bucks? Yes.

Will it throw a code? Possibly.

 

How is it worth the 80 bucks if it does exactly the same thing as your stock cat convertor does?
Now is it worth the 80 bucks if it actually works worse then the stock cat convertor? I already told you that backpressure increased by using a Magnaflow over the stock on.

And why not get it replaced for free under warranty. Cat convertors are warrantied for 8 years or 80,000 miles.

And yes, you broke the law.

 

It's too bad that the stock b-pipe narrows down to 2" before it enters the cat and is smushed at the rear o2 sensor, greatly restricting airflow. I prefer the sound of the stock unit - nice and deep and quieter than my CA b-pipe.

Has anyone done any tests on the vibrant cat to see how well it flows compared to stock?

I wonder if it would pay to cut out the vibrant and weld in the stock cat, eliminating the piping restrictions?

 

If anyone is in the North IL/South WI area, and has a vibrant cat, Id be more then willing to lend my time and my pressure gauge to test the vibrant cat. Free of charge!!!

I understand replacing the B-pipe, and I'm not trying to convice anyone not to mod there car. There is just way to many mis-informed people out there.

 

well the number one reason to ditch this factory "high flow" cat is because I don't need a 2" choke on my full 2.5" exhaust. Your exhaust is only going to flow as good as the smallest area in your system. And of course being on nitrous I'm burning alot of fuel so its obvious why this would be a concern.

#2, the reason my stock cat is going bye bye is because its bad. it was fried during an issue I had with my ICM and is begging for a replacement. no well in hell they'll replace that under warranty especially when they take one look under my hood so no reason to even waste time there.

once its all said & done I'll have a free flowing 2.5" exhaust from the header back

if you'd like though you can have my stock "high flow" cat