mikesimpalass

I could use some advice on a vibration I'm experiencing with my car, I think it might have to do with exhuast resonance but I'm not sure. I have an ls swapped gbody monte carlo with long tubes, 3 inch true duals, and summit turbo mufflers.

the vibration is present between 2100-2400 rpm . it seems to be dependent on engine speed, not vehicle speed. I can even feel it with the car in park revving the engine. I recently re did my exhuast hangers becuase I thought they were too rigid, after I did, the vibration is much less noticeable, but it's still there.

it's pretty annoying becuase my car is that rpm range while cruising on the highway.

I've seen where some people have added weights to the exhuast to nullify resonant frequencies, added resonantors, or just bought different mufflers, any advice?

ULTIMATEORANGESS

iTrader: (4)

where is your vibration most pronounced?

mikesimpalass

where in the car? I can feel it in the floor and in the seats

while driving, it seems to be most pronounced around 60-70s mph. above or below those speeds, it seems to smooth out

ULTIMATEORANGESS

iTrader: (4)

are your u joints ok and your trans mounts?

mikesimpalass

driveshaft and u-joints are new, I have a rubber trans mount which is also new.

I also considered whether or not my u joint angles were off, both operating angles are 2.7 degrees

mikesimpalass

i might have found my vibration problem. I have exhuast leaks in each side of my dual 3" pipes, just in front of my mufflers. and the escaping exhuast gases are blowing onto the floor of my car just under the seats. if this is it, it will be an easy fix!

Mongoose350

iTrader: (1)

You want a good gap between the exhaust and the car. Even if it's not touching at idle, when you increase throttle the engine may move a little and cause contact between the exhaust and the bottom of the car. It's also possible your trans mount could be transferring vibration but I don't think that would be an issue while sitting still.

mikesimpalass

I know the exhuast looks really close to the bottom of my car in the pictures, but it's actually about an inch away.

mikesimpalass

I just noticed today, that when I'm driving down the highway around 55mph, everything seems really smooth. but if I coast and allow the car to engine brake at 55 mph, I get a really strong vibration

JetMech442

iTrader: (1)

Not sure if you're experiencing mechanical vibration or exhaust induced vibration.

I'll share my knowledge/experience with the exhaust side since no ones touched on it.

What you may be experiencing is the exhaust frequency at 2100-2400 rpm is matching your cars natural resonance frequency. This setup occurred in my LS2 G8GT after I removed the rear mufflers. The fix is simple. Install a Jpipe that with a length that matches the frequency.

Googling "Jpipe G8GT DIY BIGRED585lbs" will get you to several very informational threads.

The exhaust will output a first frequency of 140-160Hz between 2100 and 2400 rpm. Download an a frequency app like frequesense or spectrumAnalyzer and drive at the offending rpm(highway usually has more load and thus more power to the drone). You should see 140-160 Hz as the highest frequency...if you do..it's drone and the Jpipe is a simple fix.

Okay, this got really long. hope it helps. If it turns out that you DO have drone, feel free to ask more questions, I'm happy to help.