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I couldn't imagine what it would sound like with test pipes. The HFC's and catback sounds insane. Getting even better as it breaks in. Only gripe is that I wish they offered carbon fiber tips as an option. The ones that come with the exhaust could be better aesthetically.
Last edited by mcervinojr; May 20, 2026 at 09:01 PM.
I couldn't imagine what it would sound like with test pipes. The HFC's and catback sounds insane. Getting even better as it breaks in. Only gripe is that I wish they offered carbon fiber tips as an option. The ones that come with the exhaust could be better aesthetically.
Fitment is good with the AFD?
I can't wait to hear how it would sounds paired with the Concept 841 headers. The 841 is epic.
No complaints from my local shop that installed it. Does take a bit of tweaking to center perfectly in the center of the valence, but I feel like that would be the case w/ any exhaust.
Would be the first Z06 on this forum to run hi flow cats without CEL after 150-300mi.
Without tuning or CELlink that is
There are no guarantees with any high flow cats, but I can report I have over 4000 miles with no cel ever. Same for a friend that had his installed a month apart. Both cars 2024 models with Milltek 200 core high flow cats.
I have Miltek high flow cats and had to use the mini cats to get past the clearance issues with the eVenturi air intake. Alas it did not solve my CEL issues either. I had to use 45 degree ones to get the clearance, but maybe the big daddy ones will fit, but I don’t think it would solve it. I got a lot of miles before the first CEL, and it will throw them quickly on track. So I just got a CELsync and left it at that. Tune will be next.
Base on my logical reasoning is that the AFD system neck/taper down through each transitions just before it reaches the massive 4" tip to echo all that high pitch sounds.
Think of it like an air type instruments. ie. Flute, saxophone etc.. How about when you whistle to create that high pitch tone. Does that make sense?
One can argue that it may POTENTIALLY create restriction and thus lose power for sounds. But this is a NA application and may not be an issue. But if you are pushing ZR1 type hp with FI, bigger is better.
The Valtronic seems to have a similar design concept and maybe Fabspeed to a certain degree.
This are the physics principles that you're looking for:
A conical (tapered) pipe is the best shape for enhancing a full, rich series of higher harmonics. Because a cone’s varying diameter allows it to support both odd and even integer multiples of the fundamental frequency, it produces a harmonic sequence of \(1, 2, 3, 4\), etc.
How Resonator Pipes Work
Resonator pipes operate by capturing and reflecting sound waves.
Reflection & Standing Waves: When a sound wave travels down the pipe, it reflects at the end (either open or closed) and travels back. If the pipe's length perfectly matches a fraction of the wave's length, the reflected wave constructively interferes with the incoming wave, creating a standing wave.
Amplification: The resonator effectively amplifies specific frequencies. The shape and length of the pipe determine exactly which frequencies get boosted or canceled out.
Why Shape Determines Harmonics
Different pipe geometries favor different harmonic profiles:
Conical Pipes (Best for Higher Harmonics): Tapering outwardly allows the pipe to behave acoustically like an open cylinder, regardless of whether its far end is open or closed. This shape naturally produces a full spectrum of both odd and even harmonics, resulting in a complex, rich, and bright tone.
Cylindrical Pipes (Closed): Because they are closed at one end, they only reflect odd multiples of the fundamental frequency. This produces a simpler, more hollow tone, typical of a clarinet.
Cylindrical Pipes (Open): These produce all harmonics (odd and even) and sound richer, but are harder to physically control across higher modes compared to a conical shape.
Helmholtz Resonators: Instead of a long pipe, these use a distinct cavity and a narrow neck. They are primarily used to target, trap, and cancel out single, highly specific frequencies (such as unwanted exhaust drone) rather than enhancing higher harmonics.
A flat plane V8 at 6,000 rpm is rotating at 100 times per second, which means it is making 400 evenly spaced exhaust pulses per second, which means it's fundamental frequency is 400 hz.
The first higher harmonic is 800 hz. 2nd order harmonic is 1,200 hz, 3rd order is 1,600 hz, 4th order is 2,000 hz, 5th order is 2,400 hz. etc.
That high pitched, ringing sound that you're hearing in the AFD exhaust is the 4th and 5th order harmonics.
A pipe that is uniform in diameter will play all of the harmonic frequencies, but they get fainter in the higher harmonics. A trumpet or trombone shape to the exhaust exit will enhance the higher harmonic frequencies, leading to a brighter and higher pitch tone.
I just installed the stainless AFD w/ mufflers and valves on my 25'. I paired it with Milltek HFC's. It sounds absolutely amazing.
I assume you transferred over the factory valve actuators from the stock exhaust right?
I have the same setup as yours but can’t get my valves to work. I even ordered a set of new actuators (P/N: 85520525, the one without the rod) but those don’t work either.
The valves and valve springs seem to be in pretty good shape so I don’t think the issue is with the valves. I can’t even do valve relearn via my Foxwell NT710. When I try, nothing happens.
I’m getting the following codes when I scan the car:
P3171- Variable Exhaust Flow Control Valve Feedback Circuit High Frequency
I assume you transferred over the factory valve actuators from the stock exhaust right?
I have the same setup as yours but can’t get my valves to work. I even ordered a set of new actuators (P/N: 85520525, the one without the rod) but those don’t work either.
The valves and valve springs seem to be in pretty good shape so I don’t think the issue is with the valves. I can’t even do valve relearn via my Foxwell NT710. When I try, nothing happens.
I’m getting the following codes when I scan the car:
P3171- Variable Exhaust Flow Control Valve Feedback Circuit High Frequency
P316E - Variable Exhaust Flow Control Valve Feedback Circuit Low Duty Cycle
P3184 - Variable Exhaust Flow Control Valve 2 Actuator Signal Performance
Are you sure that the Foxwell NT710 can reprogram the valves?
I got a Launch Creader Elite. First thing I did was plug it into stock exhaust and reprogram the valves. When it said valves successfully reprogrammed, I was like, ok I know this works. Let's change out the exhaust....
Last edited by Phimosis; Jun 11, 2026 at 06:59 PM.
Are you sure that the Foxwell NT710 can reprogram the valves?
I got a Launch Creader Elite. First thing I did was plug it into stock exhaust and reprogram the valves. When it said valves successfully reprogrammed, I was like, ok I know this works. Let's change out the exhaust....
NT710 is supposedly bidirectional and definitely has exhaust valve learn procedure in the menu but haven’t been successful with this exhaust. It did work when I installed AWE.
Before I put the stock exhaust back on, I might as well, give the scanner you mentioned a try (I heard about Launch from others too).
NT710 is supposedly bidirectional and definitely has exhaust valve learn procedure in the menu but haven’t been successful with this exhaust. It did work when I installed AWE.
Before I put the stock exhaust back on, I might as well, give the scanner you mentioned a try (I heard about Launch from others too).
The valve controllers are the stock GM part right? Maybe the linkage is binding up or the AFD valves are sticking? It could also be the valve controller position was a little off when you tightened them down (install notes says: before you start, make sure the actuators are installed correctly, as even a few degrees of misalignment can cause the relearn to fail). Maybe try disconnecting the valve controllers from the linkages and see if it will try to cycle correctly during the valve learn procedure, with no load on the valve controller? Or maybe the connectors aren't fully seated so there is a fault in the signal going in or coming out?
With the Creader, when I initiated the valve learn procedure, I could hear the exhaust valves cycle, like you went from race mode to stealth mode and back to race mode and then after less than 2 seconds it says something like "exhaust valve relearn complete".
The valve controllers are the stock GM part right? Maybe the linkage is binding up or the AFD valves are sticking? It could also be the valve controller position was a little off when you tightened them down (install notes says: before you start, make sure the actuators are installed correctly, as even a few degrees of misalignment can cause the relearn to fail). Maybe try disconnecting the valve controllers from the linkages and see if it will try to cycle correctly during the valve learn procedure, with no load on the valve controller? Or maybe the connectors aren't fully seated so there is a fault in the signal going in or coming out?
With the Creader, when I initiated the valve learn procedure, I could hear the exhaust valves cycle, like you went from race mode to stealth mode and back to race mode and then after less than 2 seconds it says something like "exhaust valve relearn complete".
Something weird going on for sure… I followed your advice and removed the actuator from the valve housing. Still had codes and relearn was unsuccessful. Then to rule out any issues with the extension harness removed the extension harness and connected the oem connectors directly to the actuator. Still had the same codes and relearn didn’t work. Weirdly I wasn’t able to erase the codes with my scanner either. Makes no sense at all to me. Wondering if there is something wrong with the scanner. Launch Creader arriving tomorrow so hopefully will have more clarity soon. Will report back.
Something weird going on for sure… I followed your advice and removed the actuator from the valve housing. Still had codes and relearn was unsuccessful. Then to rule out any issues with the extension harness removed the extension harness and connected the oem connectors directly to the actuator. Still had the same codes and relearn didn’t work. Weirdly I wasn’t able to erase the codes with my scanner either. Makes no sense at all to me. Wondering if there is something wrong with the scanner. Launch Creader arriving tomorrow so hopefully will have more clarity soon. Will report back.
I can't find the exact wording right now, but when I was reading up on the valve re-learn, it says clear any codes, then perform the valve relearn. Maybe the old codes that it threw are preventing it from attempting to do a valve relearn? And why isn't it letting you clear the codes?
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