turboholic

Thank you for the in-depth explanation James!
My car was measured on a Superflow dynamometer.
Before we call the mythbusters, do you agree that idle AFRs are not affected by any backpressure? Paul´s idle AFRs seem to be far off-spec.
In the near future I will install a second AFR sensor after the turbo (where the air injection plug normally sits after the cat) and will be able to see 1 on 1 comparison before and after turbo.

JamesE

What you see on the dyno is irrelevant. The error is there, imbedded by design. Wether you see it or not depends on the health of your lambda probe/measuring device.

When I did the test you are about to do, it was very noticeable.

turboholic

Would like to know your opinion on above question.

Also, if you say that the after-turbo dyno O2 sensor makes no sense, why should they use it in the first place? Does the car produce different exhaustfumes on a dyno compared to streetuse? I doubt that.

Regarding the pre-turbo AFR readings, the factory installed stock AFR sensor before the turbo, if that makes no sense at all and only causes erratic readings (what I seriously doubt) why did Porsche do it?

Kaefer

I'm getting ready to install a WB02 in my 930 and now I'm wondering the same. Why did Porsche install the stock 02 sensor before the turbo?

My guess is the stock 02 sensor is there to simply monitor idle and cruise AFRs, not WOT AFRs. During WOT the system is in open loop and the 02 sensor is not in use. For idle and cruise the stock location should fine (no/minimal boost during idle/cruise).

Ugh. I guess this means I'll need to weld in an 02 bung somewhere after the turbo for the WB02 sensor. Good times...