auto_god

So I realize this data is several years old now (got busy playing with my new Camaro SS 1LE!), but I recently finally got fed up with my flapper valve sticking on me and removed it and the stock muffler and replaced it with a OE replacement style muffler. Being the curious person I am, I once again installed by backpressure gauge into the same location on my truck and logged another full throttle run.................and the verdict is.............No difference! Same 6.5 psi. Now having said that, there is now no backpressure at all under normal driving. You have to be at full throttle now to observe any pressure. So once I got those results my thoughts then turned to how much of that 6.5 psi was attributed to the secondary converter (I had been taking my backpressure readings from the downstream 02 sensor bung on the drivers side). I decided to install an o2 sensor bung in front of the muffler (and obviously downstream of the secondary converter) and ran the test again. This time I observed 5 psi of backpressure, leading me to the conclusion that 1.5 psi of my backpressure is attributed to the secondary converter. After seeing the data, I've ordered a different muffler to see if that 5 psi can be banished (I'm confident it can). I'll report back when that happens!

So here is a question for those that have seen the valve inside (I have not......yet!). Does it appear that the shaft that passes through the flap is a separate component from the flap itself? Here is where my mind is at being the data kind of guy I am. What I would like to do is to remove the flap entirely from the system in a non destructive way and then redo my backpressure test to see what impact the flap really has on the measured backpressure. What I was pondering is if I were to cut off the end of the shaft without the spring (see attached image), could the shaft be pulled out of the flap allowing me to recover the flap out the intermediate pipe where it separates at the flex. I could then plug the holes where the shaft was & perform my backpressure test again. I have 2 reasons behind my interest in doing this. 1. As I stated above, I'm very interested to see the flapper valves role in the measured backpressure. 2. I really don't mind how my truck sounds (I'm at the age where quiet is just fine with me), so if this modification provided a reduction of some or most of the backpressure without the expense or increased noise levels typical of aftermarket exhaust systems, that would be a complete win in my opinion.

I realize this is an older post but thought I would share my results of doing pretty much the same test with my 5.3L a while back investigating whether a catback would be of any benefit to me. Peak pressure of 6.6 psi occurred at just shy of 5500 rpm. My cruising data was very similar to the original poster's, although with any sort of load at all above around 2000'ish rpm there would a consistent 1 psi or higher. I'll update later when I've upgraded the exhaust system and have new data from that!