I am new to the C5. I have installed headers on various types of small blocks. I have a 97 and I ordered a set of full length headers. It came with the A.I.R flanges to weld in. My question is should I delete the AIR flange and rear o2's and have them tuned out or should I install the AIR... I am confused as to what that flange actually does.

 

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Kenny

 

If you are in a state that requires emmision tests--then you should weld the AIR fittings on--just block them off--They do a visual test to see if they are installed-- No smog in your state ?? then leave them off But unplug the 2 pigtails that plug into the air pump under the left frt bumper--If you get AIR codes turn those enablers off--best is to have all the REAR 02 enablers set to "not reported" and "no mill" with headers

 

I guess I do not understand why everyone is so quick to kill EPA emissions related components.

What is the function of the AIR injection? To help fire off the cats at initial startup. What does this hurt on performance? Nothing other than less than a minute of the air pump running. So worst case is you add 4AMPS? of load to the alternator until the cats are fired off and normal operation from there.

What is the issue with leaving the catalytic converters in place? Unless you are more than 600HP at the crank there is minimal restriction with todays catalytic converters. Considering they will flow nearly 300HP each side without restriction...what is the problem with leaving them on?

I have personally tested numerous catalytic converters to see the difference in power restriction. Considering a factory set of cats from a 2002 LS6 C5 was a 3HP restriction compared to a high flow 200 cell aftermarket cat and then with no cats the factory cats showed a 6.5-7HP restriction. I hardly think it is worth the environmental impact to run without cats because at WOT heavy load there is less than a 10HP loss with them on. Mufflers and press bends are more restrictive than the cats will ever be.

I am by no means a tree hugger...but to remove something just because the internet wanna-be go fast people think we are still in the world of old bean media filled two way cats that would hold back 30+HP is pure ignorance. The only way to hurt the flow of todays cats is to run leaded fuel through them or overheat them with an improperly lean running engine.

Sorry if I sound harsh or like I am attacking, but I am a bit tired of people being told to drop emissions related items because they are hindering a vehicles performance. It is just not true.

 

Just so you know--i was not trying to advoacte eliminating the AIR system--just trying to answer his quetions on what he needs to do-On my persoanl C5 with 390 RWHP & in Calif.--I run both the air pump and have metal Hi-flow cats-- Utimately, everyone has to make to make their own decision based on their conscience as to the air we breathe--

 

Clean up the engine bay, get rid of the annoying exhaust popping on Decel, eliminate uneccesary weight, eliminte the possibilty of exhaust leaks and generally speaking less useless things to break

This just isnt true, they are a restriction, no matter how you look at it, yes high flows are better then stock, but none the less they are a restriction. They do cost HP, some more then others, but when you start increasing horsepower the % they rob starts increasing as well, and yes i have plenty of tuning and racing experience to back up my claim.

I agree that an exhaust with bad mufflers/bad bends can create just as much of a restriction on airflow as cats, but when you are trying to maximize, you should build your exhaust correctly, when done right the biggest restriction you are left with are the Cats.


If a vehicle is tuned correctly without cats, even modified ones will run much more efficiently then stock, so tell me how that is bad for the environment?

Honestly, you have a pretty strong opinion on this, warrented or not. And im sure your not gonna take my word over your own personal experience, but to say that everyone who ditches their emmisions systems is a "internet wanna be go-fast" is a bit arrogant, and im pretty certain that any of the nations top tuners you talk to are going to disagree with you.

 

If your state requires them i would keep them, to much hastle to get rid of them.

If your state does not require it, id get rid of it, there IS performance to be gained.

 

Ok...to clear things up a little and I STRESS that I am not attacking anyone. Sorry for the long reply also. I just re-read it and I want to convey what I have learned with over 20 years in the business of squeezing out higher performance from what we are handed from the factories.

Anything in the exhaust system that is not a straight through smooth pipe is a restriction. Even bends alter the flow of air and will ultimately slow the velocity of the gases. The cats of course are not straight through, but how much restriction is actually in just the cats? Minimal until the cats can not handle the CFM. This is when higher HP severely effects the equation.

Like I said before...until you get up into the 600HP range at the crank, the factory cats will flow plenty of air to not be too much of a hinderance. Too much of a hinderance, in my proven definition and experimentation, is less than 2%. 2% of 600HP is 12HP. Anyone who is used to 500+HP from their car will not feel another 12HP. It is hard to feel 12HP in a Honda Civic let alone something that weighs in at 3200lbs dry.

Example...612HP compared to 600HP in the quarter is worth no more than 0.060 of a second if the driver is that perfectly consistant. But then is the car used on the track 1/4 mile at a time exclusively, or is it a daily/weekend driver that sees the track once a month or once a season? Lets put that increase in speed/acceleration in a daily driver sense. Is a guy going to notice he arrived home 0.4 seconds faster on his 5 mile commute? I know there are some busy and competitive corporate folks who drive corvettes, but I highly doubt the noticeable difference.

The factory exhaust is large. In turn the factory cats are high flow large inlet and outlet ports. Cats are a medium designed SOLELY to produce a chemical reaction which burns off excess gasses in it's material. On the other hand the muffler is designed to absorb sound energy which slows the velocity of gases leaving the system. Slowed velocity will directly equate to lossed power. Many people/shops do not take the time to "test" what they are putting on in any combination of what they are putting on. Most of the time a shop will sell a combination of things to get a 20HP increase (without a PCM tune) from the factory setup like headers, X-pipe without cats, rear section with aftermarket mufflers. Not paying attention to the fact that the power loss in the system was the factory manifolds and worse yet the mufflers. I have tested damn near every combination of what is currently on the market. The factory cats are not a power killer on motors less than 600HP on my dyno.

I do not agree with this even slightly. All harmful pollutant gases can not be controlled with just a proper tune. That is the sole job of the catalytic converter to burn these emissions off as they are a direct and nearly uncontrollable by-product of a gasoline burning internal combustion engine. Can you reduce the amount of emissions over a factory tune not running cats with a perfectly dialed motor...definitely. But to remove a component that will do nothing more than compliment your tuning skills with even less of a carbon emission with minute power losses does not make sense to me.