[Umbriel]

Originally Posted by Jhunsberger

So if it is a monetary reason for not doing a tune, why not buy the headers, save up for the tune, then do it together. That way you dont risk anything. Just like someone said, things come up.......so you put the headers on with the thought of saving for a tune in a few months and it turns into 6-12 months. At that point you are putting header on for what, the sound, and risk possible damage or drivability issues? Its just the way i think and operate, just do it right the first time, end of story. Nothing is inexpensive these days, let alone moding a modern day performance car.

It probably does add a little but of horsepower but not much not being tuned. I personally would never do it that way because I would want the full benefit of what I am adding to my car but I am financially stable enough to do it. I am not going to criticize someone for not tuning if they are piecing it together and do it that way though.

[Fraxum]

Can someone please explain to me how a better flowing exhaust disrupts AFR? I am not being sassy here, maybe I am missing something.

Anyway headers without a tune on an LT1 may not get all of the HP you get from LTs alone (15 rwhp) but you will see most of it as Chevy did not leave much for us in the LT1 tune in a near stock LT1. But absolutely you will get O2 CELs without a tune. But otherwise you will not notice a performance difference with or without an ECM tune with just LTs.

And if you do not tune you can pull the headers out and sell them and not get the tuned car value hit. Now you could sell a stock appearing car as stock, but if you do you are not an honest person.

And besides all that headers just ruin the great and manageable stock sound of the LT1 and LT4.

[RyanR623]

Originally Posted by Fraxum

Can someone please explain to me how a better flowing exhaust disrupts AFR? I am not being sassy here, maybe I am missing something.

Anyway headers without a tune on an LT1 may not get all of the HP you get from LTs alone (15 rwhp) but you will see most of it as Chevy did not leave much for us in the LT1 tune in a near stock LT1. But absolutely you will get O2 CELs without a tune. But otherwise you will not notice a performance difference with or without an ECM tune with just LTs.

And if you do not tune you can pull the headers out and sell them and not get the tuned car value hit. Now you could sell a stock appearing car as stock, but if you do you are not an honest person.

And besides all that headers just ruin the great and manageable stock sound of the LT1 and LT4.

Look up closed loop vs open loop fuel system. Basically the headers allow the engine to breathe better. Which in closed loop is fine the ECU will read the O2 sensor and adjust, but once it goes open loop it uses preset tables. Open loop is generally used once you hit a certain throttle position or RPM, but not sure how the system works in our cars.

Long story short, you will run a tad lean in open loop because the ECM isn't adjusting for the extra air.

[KingLT1]

Originally Posted by Fraxum

Can someone please explain to me how a better flowing exhaust disrupts AFR? I am not being sassy here, maybe I am missing something.

Anyway headers without a tune on an LT1 may not get all of the HP you get from LTs alone (15 rwhp) but you will see most of it as Chevy did not leave much for us in the LT1 tune in a near stock LT1. But absolutely you will get O2 CELs without a tune. But otherwise you will not notice a performance difference with or without an ECM tune with just LTs.

And if you do not tune you can pull the headers out and sell them and not get the tuned car value hit. Now you could sell a stock appearing car as stock, but if you do you are not an honest person.

And besides all that headers just ruin the great and manageable stock sound of the LT1 and LT4.

There isn't a lot of room to add power and not bump into the peak torque limit on the stock tune. Also the o2's are moved further away from the engine with headers and they do not switch the same because they run cooler. So you have to adjust a o2 threshold table in the tune and disable a host of o2 codes that will pop up aside from touching up the fueling in the MAF calibration.

[TJay74]

Originally Posted by RyanR623

Look up closed loop vs open loop fuel system. Basically the headers allow the engine to breathe better. Which in closed loop is fine the ECU will read the O2 sensor and adjust, but once it goes open loop it uses preset tables. Open loop is generally used once you hit a certain throttle position or RPM, but not sure how the system works in our cars.

Long story short, you will run a tad lean in open loop because the ECM isn't adjusting for the extra air.

Newer GM cars only stay in Open Loop for about the 1st 60 seconds of start up, that is a Federal mandate. After the 60 second time frame they need to transition over to Closed Looped operation.

The reason for that time frame is it takes that long for the cats to light off and for the O2 sensors to start reading correctly.

[RyanR623]

Originally Posted by TJay74

Newer GM cars only stay in Open Loop for about the 1st 60 seconds of start up, that is a Federal mandate. After the 60 second time frame they need to transition over to Closed Looped operation.

The reason for that time frame is it takes that long for the cats to light off and for the O2 sensors to start reading correctly.

Ah, yeah it's been a while since I've messed with that stuff or read up about it. Back when I was tuning it was usually closed loop until it hit a certain RPM or throttle position. It was always turbocharged cars so probably was different.

Is it like that for all newer cars now?