Hi guys
I'm thinking of replacing my cat with a high flow to open things up a little bit. I'm running straight pipes at the moment. My car isn't really loud at idle but the second you step on the gas it starts screaming. How much louder will my exhaust get with a new cat? I like not having a muffler as it's legal here and I don't care to see it blatantly under my bumper.
Thanks guys
Alex

 

the cat wont affect sound much at all.

 

If you're going from a stock cat to a high flow, it should at least be noticeably louder. Nothing crazy though.

 

I replaced my original cat that came with my car with a highflow catco. I did notice the car being alittle louder. I do think the orginal cat my have been alittle clogged. Now i have a catco high flow cat and I have better gas milage and the car seems like it drives and preformes better.

 

Don't blast me but....

Cats are a FEDERAL requirement. Meaning, they are required in ALL 50 STATES, regardless of emisions testing or not, or what you've been told.

But for your question....
Cats can help tone down & mellow out any raspiness you might have. My car is a 2-way Magnaflow (3-way is what was put on our cars) and despite my car being "technically" illegal (no more smog pump or the air tube) my #s are so clean, they were very surprised for a 190,000 mile car!

My last test before moving to a non-emissions testing county here was:
Mar 15 2007, 02:56 PM

High Speed-2692rpm
HC 220-limit.........4-my reading
CO% 1.20-limit........0-my reading

Idle
HC 220-limit.........16-my reading
CO% 1.20-limit........0.01-my reading

 

WOWSER, your car runs with like, like no pollutants coming out at all. That's crazy, I bought a 3-way, which should actually do better than your 2-way, as I also removed my smog parts and was hoping my car would pass emissions. Seems like I should be fine, since I will have replaced all tune up parts including many sensors and relays before I test her. Kind of a thanks for letting me know I shouldn't be worrying so much.

P.S. I hate the way cars sound without cats, that unnecessary rasp it gives. Of course, bigger motors make this sound better too, so...

 

If you don't have a smog pump on your car anymore, having a 3-way is pointless. The tube is for the "third way" & the lack of pump & tube going to the cat, will only throw a flag, that something is missing.

 

How can that be if it DOES NOT have an air tube in the first place?

I don't see Magnaflow messing this up...

This is what I have.
http://www.summitracing.com/parts/MPE-94109/

 

Hmmmm....I always thought 2-ways didn't have the tube & the tube was for the "third way"/3-way cats. My bad.

Thats the cat I have too, so you should be CLEAN.

I'm in a non-testing county, but cats still hafta be there visually. I could gut it, but why bother? To gain like 2 or 3 hp?

 

Oh, well alrighty then CLEAN it is.

Three-way

Since 1981, three-way catalytic converters have been used in vehicle emission control systems in North America and many other countries on roadgoing vehicles. A three-way catalytic converter has three simultaneous tasks:

1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2 (THIS DOES NOT HAPPEN IN 2-WAY CONVERTERS)
2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + 2xO2 → xCO2 + 2xH2O

These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine running slightly above the stoichiometric point. This is between 14.6 and 14.8 parts air to 1 part fuel, by weight, for gasoline. The ratio for LPG, natural gas and ethanol fuels is slightly different, requiring modified fuel system settings when using those fuels. Generally, engines fitted with 3-way catalytic converters are equipped with a computerised closed-loop feedback fuel injection system employing one or more oxygen sensors, though early in the deployment of 3-way converters, carburetors equipped for feedback mixture control were used. While a 3-way catalyst can be used in an open-loop system, NOx reduction efficiency is low. Within a narrow fuel/air ratio band surrounding stoichiometry, conversion of all three pollutants is nearly complete. However, outside of that band, conversion efficiency falls off very rapidly. When there is more oxygen than required, then the system is said to be running lean, and the system is in oxidizing condition. In that case, the converter's two oxidizing reactions (oxidation of CO and hydrocarbons) are favoured, at the expense of the reducing reaction. When there is excessive fuel, then the engine is running rich. The reduction of NOx is favoured, at the expense of CO and HC oxidation.

Just a little wiki information.

 

When you test the car, come back & post up your results, or PM me with them.

I now wonder if mine is a 3-way? I bought the car from a friend who had put the cat & LS1 cat-back on, amout 2 months before I bought the car from him so......

 

Whoa, that's alotta good info. Thanks guys

 

Every little bit counts! I just paid for a new one so there is no way I'm gutting it just to have to buy another..

 

did i read this correctly? you are running straight PIPES not PIPE!
if you have true duals then you will need 2 cats.
if by PIPES you mean they split off the single pipe into two pipes then one will do.
nice place to live - no muffler required.

 

Sorry, straight pipe. I might put true duals on it at one point, when I get headers, but no time soon