Popping noise at 2500 rpm with DPI exhaust

[DaraSue]

Continued from this thread: http://dmctalk.org/showthread.php?18...nsor-grounded/

I had my car in for emissions and the owner of the shop (who may or may not actually be a mechanic) said he heard a misfire. The sound he was talking about is a light popping noise at high idle (2500-3000 rpm), similar to the gurgling noise when decelerating. I don't really notice it as much when I'm driving but it's noticeable when I'm standing outside the car.

My buddy who also has the DPI exhaust listened to it and says his makes the same noise. Does anybody else with the Spec exhaust experience this? My car had a leaky injector seal and fouled plug on the #6 cylinder but it still does it after replacing the seal, cleaning up the plug, replacing the o2 sensor, and tightening a bunch of loose nuts on the exhaust manifold.

Is this actually anything to be concerned about or something commonplace with this exhaust setup?

[dmcnc]

You're probably talking about the exhausts crackle effect when you let the throttle go.
https://www.youtube.com/watch?v=kNtL6EfPgRI

[DaraSue]

You're probably talking about the exhausts crackle effect when you let the throttle go.
https://www.youtube.com/watch?v=kNtL6EfPgRI

Yeah, I've noticed that before but what I was specifically concerned about was hearing the noise when I hold the throttle steady at 2500, unless whatever small variation in pressure is enough to make it crackle the same way.

[FABombjoy]

Kjet will lean out off-throttle as the meter plate closes. If everything else runs correctly its probably a lean misfire during a no-load condition. It’s a little unburned fuel igniting in the exhaust. Some people like to tune this in on purpose. The decel valves offset the effect a little.

[David T]

Two ways to reduce that popping. Experiment with the springs on the decel valves or add a dashpot to keep the throttle valves from slamming shut.

[FABombjoy]

Whoops, re-read and saw that this is when holding throttle steady but in a no-load state? Or is this when cruising?

I still wouldn't be concerned. It seems like having such an overall short exhaust system makes for a fair amount of exhaust feedback based on actual air/fuel ratio. Lean will pop/crackle, especially on decel. Too rich is kind of "arrhythmically thumpy", it's hard to describe since it isn't as noticeable as lean afterfires.

A functioning lambda system guarantees that you're never at a steady air/fuel ratio, unless the engine is very cold or your at wide-open throttle. It's orbits somewhere around 14.7:1 but will never settle down.

If you're at a cruising state near 2500RPM, you're pretty close to peak torque and the engine really prefers to have a little more fuel around this point. This might be why?

[DaraSue]

Whoops, re-read and saw that this is when holding throttle steady but in a no-load state? Or is this when cruising?

Yeah, it's with the car parked and revving it up to 2500 - 3000 rpm (such as while checking dwell or doing an emissions test) . I've never really noticed it much while driving but idk if it's because it isn't doing it or because it's harder to hear from inside (although I do notice the decel crackling while driving).

[DaraSue]

I chatted with Josh and he suggested I might need a valve adjustment. It's been about 20,000 miles since it was done. I don't want to attempt it myself and my experience with local shops has been underwhelming so hopefully my engine doesn't explode on the way to Seattle...