How does changing headers, exhaust, cats change the air to fuel ratio? I just dont understand as all it does is help it breath out better. I can see this with any engine mod such as intake, plenum, heads... But mods after the engine I just dont understand.. Sorry if this is a stupid question but I like to know the ins and outs before i buy something..

 

O2 sensors incorrectly read the gases in the cats, making it think the engine is old, so it adds more fuel in the cycle.

 

Is this something we need to be concerned about when just adding these simple bolt on parts?

 

Im not sure as Iv heard that when you add the Plenum, headers, and high flow cats that people are running lean which means an ECU tune is right around the cornor along with some dyno time with a A/F meter..

 

yes.. I've heard that as well and its a bit disconcerning..

 

yea but it just makes you get your butt to a dyno and get some A/F readings.. No biggie as iv never been to a dyno..

 

actually...

reads HOT with NO or Less cats and takes in more air to try and COOL...

 

How does it read hot in the absence of something that superheats the air?

 

my .02

The extra breathing allows better emptying of the cylinder, thus there is lower pressure and more of the intake charge gets pumped in, thus the engine will need to add more fuel, hopefully the engine will adapt for this, but it depends on the motor and the ECU

 

cats cool off the exhaust gasses...

 

Ohhh so your saying that you will only/probably have a problem when you replace the cats with High-Flow or Test Pipes.. Cause I have an intake and plenum and next mod will be high flow cats with the Nismo exhaust. I just want to know if I will expect a change in A/F that I might have to get my ECU tuned...

 

Catalytic converters are only useful when they reach operating temperature which is extremely high. Please enlighten me on how this cools exhaust temps. Converters work appropriatley in excess of 1800 degrees F. This is much hotter than the air in the manifold. In fact, this temperature on a EGT gauge is indicative of a lean running FI motor measured near the exhaust port on the head. The cat is obviously not attached to the head. The exhaust without the cat, in the location of the cat, would be an untested, unvalidated, guessed upon by me, 650 deg. F or so on a normal running NA motor. How is that hotter than 1800 deg?

 

ask Techno Squre...

last I heard them comment on the apparent "lean" cituation (which I never experienced on my car with RT Cats) it was because the added heat the O2 sensor reads after the cat makes the car run lean...

Ask them... or MR Twisted will explain what TS said...

 

The O2 sensors read more fuel in the exhaust which makes it think the motor is rich which will make the ECU lean the mixture up. Has nothing to do with heat. There is always unburnt fuel that makes it through to the exhaust and the cats normally burn this off. This is one reason why I think it is a good idea and one reason I am installing a HKS Twin Power Ignition when I put the XERDs in on Friday. To help more completley burn the mixture before it enters the exhaust. This is much more plausible than the heat argument especially considering an O2 sensor measures AF ratio and not EGT. If it measured EGT we could all splice into the O2 sensor for our EGT gauges. You can't. More specifically, an oxygen sensor senses the amount of !!!oxygen!!! in the exhaust, thus the A part of the AF ratio. The F comes by way of subtraction.