If I go from stock to LT’s will my A/F change? Someone told me his went rich when he put his headers on. I am trying to figure out the science on this but can’t. Unless he had a leak before the O2’s I’m not sure how it will change the A/F.

 

MIne did and the EGR goofed up as well.

 

You will usually run a little richer after putting headers on..

 

Mine ran richer, but I dyno'd before LTs with no cat, so some of the cars that are running richer after LTs may be because the cat soaks up some fuel.

 

Bummer.
I think mine is running rich already.
Anyone give a guess why it does this?

 

i dont see how you could run rich just from installing headers unless you didnt get them sealed up well before the O2 sensors.

 

when you allow the engine to "breathe" you are introducing a better scavenging effect. Headers and good ones will have a"vacuum" that pulls the exhaust out due to the design of the primaries and how they are configured. So you run richer because of the better ability for the engine to breathe

 

I would agree.... on a mass-air car (94 and newer) installing headers should not change the A/F ratio. What may be happening is 1) the previously mentioned air leak before the O2 sensors; 2) the O2 sensors not reaching the proper operating temperature because they are farther from the engine; 3) poor quality O2 extensions; or 4) burned plug wires causing misfires. All of these might make it run richer.

But, assuming you have done everything correctly, the PCM should still be able to hold the A/F ratio at 14.7:1 in closed loop/low, moderate load driving. And that should carry over to the WOT scenario, in power enrichment mode.

 

grygst76 is right...

Good headers will create a natural exhaust vacuum that will reduce exhaust back pressure. Without as much backpressure, there will be less exhaust gas recirculation (hence the impact on EGR function). The engine will be drawing in more clean air instead of recirculating exhaust gasses which will also reduce your fuel economy.

This would be particularly a problem for the LT4 because EGR function occurs in the heads as a result of the significant overlap of the LT4 cam.

As for running rich, this should not be occuring. The computer should be able to compensate by reducing the EGR cycle (LT1 engines only). If you are running an LT4, I would not be too surprised to see a slightly richer mix.

Good luck...

 

whoops I did not mean it would make your car run richer, but only slightly I have been

 

Mine is an LT1.
But the one I was talking about that went rich is an LS1.

Thanks.