JimMueller

iTrader: (9)

I had my engine overhauled recently and I since the car was given back to me I now have a resonance between roughly 2000-3000RPM that shakes the cabin and rattles the contents of the center console.Same ATI non-underdriven crank pulley, new OEM motor mounts, new OEM tranny mount, replaced cats in y-pipe with straight pipe, same LS7 clutch, same OEM aluminum driveshaft, new axles, stock 10-bolt rear-end was rebuilt during the same time frame. I'm not seeing any rubbing witness marks from the exhaust hitting the chassis, although I just noticed that the clamshell exhaust hanger fell apart and we have that side supported by safety wire for the moment., But after using the safety wire, the resonance continues. The car was on a 4-post lift last night for some cleanup tasks so I couldn't check all angles, but my digital level said the bottom of the oil pan, bottom of the tranny, and driveshaft were all very close to 1*, the axle was hanging so I didn't measure it.

Any ideas how I can isolate and eradicate the resonance?

HioSSilver

iTrader: (8)

Lots of stuff can cause nvh issues. It could be something as simple as not tie wrapping wires or the throttle cable down. I have seen them vibrate the against underside of the cowl. I had the right rear tail light make a vibration once. Took me forever to find that.

Floorman279

iTrader: (11)

where is your exhaust exiting the vehicle

JimMueller

iTrader: (9)

Full exhaust, SLP Dual-Dual over the axle, cutout capped.

Floorman279

iTrader: (11)

check for leaks at cutout?

wannafbody

iTrader: (2)

I have a resonance at 1900 rpm with longtubes and catted y. Get past 2000 rpm and it disappears. Could just be your exhaust configuration.

HioSSilver

iTrader: (8)

Yea sometimes just changing tip configuration can change sound/resonance greatly.

99 Black Bird T/A

iTrader: (4)

FWIW - My 99TA picked up a resonance noise around 1,500 rpm after the RPM Magnum install, new hydraulics, CF drive shaft & RXT clutch. It's minor but my guess is something in that list isn't secured as previously.

Floorman279

iTrader: (11)

this is why people put down sound insulation in these vibratory machines. i will be doing that in a year or 2 i think.

JimMueller

iTrader: (9)

It didn't behave that way before the car was towed to the shop, so I'm just hoping it's something simple that has been overlooked without a requiring a wild goose chase.

G Atsma

Have you checked for ANY spot the pipe(s) might be contacting the chassis? Just touching in one spot will resonate like crazy!

HioSSilver

iTrader: (8)

No it's not. But it is why people use zip ties and/or why people should put stuff back in it's holders.

I mean they're pretty quiet cars stock till people mess them up.

JimMueller

iTrader: (9)

I was very happy with my vehicle, even with 850/375 springs and a full rod end rear suspension, before the overhaul. Now I'm frustrated at having to chase little things that were correct prior to the overhaul. I no longer look forward to driving it.

HioSSilver

iTrader: (8)

Damn that's alot of spring for a street car. I couldn't stand the rod ends in my car. I changed them out to adjustable bushings from ridetech.

JimMueller

iTrader: (9)

I replaced the rear passenger side clam shell exhaust hanger today and removed the safety wire, and replaced my wideband sensor. Still have the same vibration. The only tight spaces are on the driver side (pipe is already flattened) where it makes a bend towards the center of the car (it looks like the body is slightly polished here above the bend) and where it crosses over the cross brace attached to my decoupled torque arm. Right now the brace is lowered by a pair of 1/4" spacers, and there is some sort of foam or rubber material zip-tied to the brace right below the exhaust pipe to prevent metallic noise. With the engine off, the pipe has maybe 1/8"-1/4" clearance to the foam if you look at it from the ideal angle.

I don't see a way to raise the exhaust, so I'll check with the engineer that designed the TA to see if there are any concerns with lowering that brace further. I don't want to blindly run into some funky geometry problem.

The cross brace from the front:

JimMueller

iTrader: (9)

The PE (physical engineer) that designed this torque arm says not to lower that brace at all, for both structural and geometry reasons. Not sure where to go with this now... will solid or poly motor mounts reduce NVH that far back from the motor compared with the current setup? The ARH header primaries tuck up very well, as does the ARH y-pipe. There aren't any hangers between the heads and the brace, nor between the brace and the post-axle hangers. Raising the post-axle hangers only tips up the exhaust starting where the y-merge connects with the cat-back, which is after the brace and doesn't help. Welding something to the y-pipe and then bolting it to the floor certainly doesn't seem to be a solution that would reduce NVH. Any ideas?

wannafbody

iTrader: (2)

Are you sure it isn't drone from removing the cats?

JimMueller

iTrader: (9)

Honestly, no, I'm not sure. I did have an offer to buy a very lightly used ARH y-pipe that I could try installing. But it's more than just audible, I can feel it in the seat...it's like a soft fast thumping I can feel at idle, that generates excessive vibration in the cabin between 2000-3000RPM. I'm not above 3K that often yet, but the few times I have been the vibration/thumping seems to disappearr above 3000RPM...no, it's not reasonable to only drive the vehicle above 3000RPM

Darth_V8r

iTrader: (4)

Sounds like it might be hitting the seatbelt bolts in the tunnel