Altering Header Resonance

[Hambone!]

I'm reasonably certain this is the proper place for this post, as the question is not entirely exhaust related, but also tuning and mechanical black magic. I have an LS3 / TVS 1900 combo with a set of Pacesetter long tube headers. The problem, is the headers generate a frequency the knock sensors keep picking up and the PCM pulls timing. Is there a practical way to alter where the headers resonate? Clamp or weld a piece of metal to them? Dimple them with a hammer? A realllllly big hammer? I know considerations can be made in the tune, but just trying to eliminate as many issues as possible. Is this feasible. or just tune around it?

[CFster]

If it was my car I'd try a couple flex pipes after the headers.

[TheJDMan]

Would something like this work?

http://www.speedwaymotors.com/Speedway-Auger-Style-Muffler,1736.html

[funcars]

Instead of modifying the headers you might want to try to isolate the knock sensor more. Basically you reduce the signal levels getting to the sensor so it does detect knocking at low levels. Putting on an extra fitting between the knock sensor and the block with teflon wrapped threads on both ends can help. Do a little research on knock sensor isolation and you will come up with other techniques too.

Good luck

[Hambone!]

Would something like this work?

http://www.speedwaymotors.com/Speedway-Auger-Style-Muffler,1736.html

Interesting....and cheap enough to give them a try.

[Hambone!]

Instead of modifying the headers you might want to try to isolate the knock sensor more. Basically you reduce the signal levels getting to the sensor so it does detect knocking at low levels. Putting on an extra fitting between the knock sensor and the block with teflon wrapped threads on both ends can help. Do a little research on knock sensor isolation and you will come up with other techniques too.

Good luck

I suppose isolation could help, but that would desensitize them all the time. I'd rather have them always active and listening for detonation as this is a supercharged engine. If I could move the interference out of their listening range, I think I'd have the best solution.

[exwestracer]

Your idea of welding strips of metal to the tubes should also work, but there's really no way to predict where the problem is coming from... You might have little strips of metal all over the place before you stopped the problem.

Another angle would be to use (assuming they'd fit) a larger tube header. Since the engine is supercharged, exhaust scavenging isn't such an issue. Larger header tubes should result in a lower frequency pulse due to the slower exhaust gas velocity in the tubes. I believe the knock sensor software is looking for a pretty specific voltage signal, so it shouldn't take much of a change to get you out of that window.

[Jim Nilsen]

I keep wondering about whether or not you will just make it to the vavletrain noise and still have a problem? I asked about a knock sensor for my efi system and was told that my valvetrain noise would be setting it off and they told me I didn't really need one. You situation is a lot different to a point, the real thing to think about is how you can do it without while you are trying to make it work. Sometimes asking the right questions at the right time to some people can make your life a lot easier, getting something you think you need is customer service, getting what you really need sometimes takes guidance from others to solve the problem and that takes the right questions.

I worked with a vibration anylist for a while and his saying was "add mass" you could just play around with stainless steel band clamps and place them in different areas on the header to see what happens. You can then easily remove the clamps and know where to put the extra steel and how much. You could also try to make a bracket that would hold the collector area to the engine to make it more ridgid also adding the mass of the engine, but this could also cause another frequency that might not be good?

Goodluck, problems like this are hard to solve with little money invested, hope it doesn't go too deep for you.