[Chris Bryant]

I have an AEBS header with stock exhaust. All heat shields from the cat aft remain in place. From the day the header was installed, I noticed a resonance at certain RPM's *under acceleration*. At first I thought it was the header. After checking each month to ensure that all bolts are tight, thumping the collector, flex-pipe, cat, and b-pipe, I know that nothing is rattling loose. However, I noticed how THIN the heat shield ABOVE the cat and b-pipe is. Man, it feels like tin(though it's probably cold-rolled galvanized). Anyway, I am considering spraying this shield with an underbody coating, or some other high-temp, grime-resistant material. This should eliminate this LARGE, amphitheater shaped piece from resonating.

Anyone have a similar experience? If so(or even if not), any suggestions? I'm all ears, as it were.

 

[spnx]

I think that it's unlikely that it would be rattling unless it's touching. Has the bracket that holds up the cat rusted away?

This often happens, and it can leave the cat free to bang against the shield.

I've installed three shortshifters, and the last one I did has this problem.

Also, if you put undercoating on the cat shield, I think the high temps there might burn it off, or at least make your car smell. I don't think that's a good idea. You could attach some dynomat to the other side of the shield, where it's right against the body though. I know people have done this.

 

[Ben]

There is mention of this noise on SE-R.net. "They have been some complaints of a rattle or chirping noise that both headers make at approximately 2500 rpm. To me it sounds like a cricket chirping. This is not harmful and not all cars do it. I am not sure of its root cause. The new generation Stillen and Hotshot headers do not seem to make this noise."

 

[Chris Bryant]

Nope - no rust(98' SE/southern car).

Putting some type of material on the *back* of the heat shield is a better idea. Not sure that dynomat could withstand the heat & grime, though I've thought about it.

The sound is strange, almost like it is created inside the pipe. But it definitely eminates from under the car, not out of the exhaust pipe.(once cruising, the resonance goes away - only happens under acceleration).

Thanks for the input.

 

[spnx]

I think you hit the nail on the head with your last comment. If the primary walls aren't too thick, like in my 1st Gen Stillen header, you will get some sound.

My car makes a "rattlesnake" sound under hard acceleration, but I kind of like it. It may be something you just have to get used to.

 

[brian]

ya, it is a common problem with em' headers are tuned to make each cylinder "hit" the same and get each stroke exactally the same on each cylinder, and when it hits a certain rpm, it will have sort of an effect as to make a resonance, my hotshot did it, my stillen does not.

 

[Chris Bryant]

I knew there would be *some* additional noise when the primaries hit their resonant frequency, but this amount is surprising. However, if you have seen an AEBS in person, you notice the primaries look like a small pipe organ(long and large). Guess it could just be the header and nothing else.

And I am used to it(and kinda like it).

But I know I'll like it more with a Courtesy exhaust on it(in due time).

 

[brian]

ya, I think with the longer primaries it will resonate more (kind of like a pr cai) also on the dimater of the primary, how big the secondary is, ect, all of that comes into play, that is why (theoretically) a 4-1 header works better than a 4-2-1 header, I know my car runs better with the 4-1 on it (really good on the top end though)