My AFR was a little under 12:1 at boost.Haven't been on a dyno since i installed the TP.wondering what my AFR is now.Any guesses...?

btw: I'm running a stock Vortech

 

leaner than 12:1? cant offer an exact value and i doubt anyone can...

 

You will have to forgive my possible ignorance, but it is to my knowledge that a test pipe will not cause you to lean out your motor.

If you are having your car dyno'ed for power, adding in the option of having your A/F pulled as well - it is possible that you will be a bit lean. However, this all depends on the location of the wideband.

A test pipes location is in your exhaust... after the motor. It will not affect how much fuel, air, or spark is going through your engine.


From this point is knowledge that I have learned over time, however a few points may be incorrect. Before taking it for gospel, please have another member either verify or deny this.

Your primary o2 sensor (located in your exhaust manifold) is used specifically for giving the ECU A/F feedback. It tells your ECU to add/pull fuel to compensate for the air flowing through the engine.
Your secondary o2 sensor (located in your cat converter) is used as a backup reading for your first. However, it's primary use is to ensure that your car is running clean and the cat is doing it's job.

If you have replaced your cat converter with a test pipe, without using the proper corrections (manual or electronic fix) it will cause your check engine light to come on. Once this does, it is possible that your vehicle will change to a 'safe mode'.

 

Why would a test pipe lean out a car?

 

The cat normally is restrictive compared to a test pipe. When you slap on a test pipe, more flow out means more flow in. This extra flow could possibly lean everything out a few points, but it really depends on the car.

It's been observed by some locals here running testpipes or exhausts and FI. There's also been a few similar cases with members on s2ki.

 

There's a thread just a few posts down from this one about this very issue...

https://www.s2ki.com/forums/index.php?showtopic=442563

ya@inline: "Thats why i said MOST of the ones WE'VE seen and dyno'd very lean. Yes the exhaust system AND the test pipe cause them to lean out."

From my personal experience, a testpipe alone is enough to lean a stock CTSC >13

 

pretty much like elusiv was saying that when your cat is on it reduces the flow of the exhaust, but when you add a testpipe the exhaust flows right through and therefore not letting the gasses buildup where the primary O2 sensor is which will lean out your A/F ratio

 

You don't run a wideband?

I can tell you once I install the TP. I have put on the exhaust and it leaned me out on that according to the gauge .5-.7 leaner.

But like you said, getting to the dyno will give you the best.