re-rattling

Shamrock

Sorry guys for the bump. I just haven't found an answer and I thought maybe to ask the question differently. After I gutted the stillen sports cats and tuned with up-rev, I started to hear a "rattling" noise at 3000 to 3500 rpm (it only occurs at these revs and in every gear.) This doesn't happen when I rev in neutral;only while driving. I tried to video it but it just isn't loud enough. It's a separate noise then the "rasp" that people claim comes from the cats after gutting; however, maybe it is a sound caused by resonance due to the gutting of the cats. Either way it's got my panties in a wad. I couldn't reach a conclusion as to what it is but maybe you guys can tell me what it isn't. I've read so many horror stories about things like crank noise or "knock." Could it be timing? Knock? Crank? Thanks

Shamrock

C'mon people. Any ideas what it isn't before I go crazy taking things apart? Or more importantly before i make others crazy taking things apart. Thanks!

Zoren 370

Just for clarification when you said gutted the cats do you mean removed it / delete and replaced with a straight pipe?

Try checking the exhaust heat shields under the trunk they do rattle at wot or try test pulling down your exhaust pipe it might be hitting the cross brace bar at the center.

I had to do a washer and nut mod to bring it down( the cross bar) or clamp your exhaust at the rubber exhaust hangers to pull the exhaust up.

That was the case about mine. I only hear a rattling sound at that rev 3000 up.
Now it gone. Btw I placed a dynamat on my heat shields.

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SouthArk370Z

Two guesses:
1) The piping is moving a lot at certain RPMs and load and striking something on the frame or other parts of the car. Try adding some weight at different points in the piping to dampen resonance.
2) Internal resonance as you talk about in the OP. Adding a little restriction may help but may just move the "rattle" to a different RPM.

Good luck figuring it out.

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Shamrock

Thanks guys. Good ideas. I gutted the cats and put them back on. So no one thinks it's timing, knock, or crank? I tuned with up-rev after the gutting and that's when the rattle started. I was thinking maybe the rattle was from a bad tune, but what do I know? You guys are the masters!

Zoren 370

Btw this is the cross bar Im referring to. My resonators are hitting this bar at revs.

image.jpg

I hope you find it. I know its annoying as it took the fun out of my Z for awhile.
Worst case just get a test pipe to replace your gutted cats.

Shamrock

Got ya. I'll check. Could it be however any of the above engine issues?

SouthArk370Z

If the rattle is not in the exhaust piping, get an OBD scanner and monitor the oxygen sensors, knock sensors, &c.

__________________
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Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

Shamrock

A problem like that wouldn't cause the engine fault light to light up? I used the up rev prg to get the ecu to ignore the oxygen sensors because after the gutting the engine fault light lit up.