If I'm cruising around, anywhere from 4th to 6th gear 2000 rpm and above and I give it some throttle, the car kind of vibrates, gets real doggy, and gives a rumbling/vibrating sound. Is this normal for the LT1/T56 in such a low rpm range, or is it a problem with the clutch/tranny or engine itself? I can't figure it out. Thought maybe motor mounts, but doesn't really fit the picture. I have neck snapping throttle response in the lower gears/low to high rpm though, it's just real different than that in the powerband I stated above. I'd appreciate any insight, as this really bothers me - the doggedness AND noise.
Thanks

 

I'd guess that either your driveshaft is out of balance, or the exhaust is hitting the floorboard

 

TTT for ya

 

Hey thanks. I thought the exhaust also, that's why I paid careful attention when we put the Hooker in this weekend to make sure I had 'space'. It did the same thing with the flowmaster catback, and still with this catback and I know it is not hitting ANYWHERE. But, I can't confirm the Y pipe isn't hitting. Tried seeing if it is, but I can't for sure. It's the SLP Y that comes with the shorty headers, and I didn't put that in. Soooo, maybe that? What would I have to do, drop the Y?
Thanks

 

I highly doubt the Y-pipe is hitting...maybe it's hitting the crossmember? What speed does the vibration start? If it's 80mph and up, it's most likely the driveshaft...

 

I noticed your Sig states you have a ES trans mount bushing. When you install it, did you install the little plate with it as well. If so, remove that plate and it should help.

I read on this Forum that the Plate was not made for our application but the ES instructions said to install it. But when you call ES they tell you NOT to install it in a 4th Gen F-Body. I was getting some vibration in my car too but at idle and when I pulled the plate off, about 65% of the vibration went away. I then told my friend "Maldo" who has a 97Z with an ES bushing how well it works and he should remove the plate from his M6 equipped car. He did it the very next day and said he could not believe that almost all of his vibration went away. I would try to pull that plate off first and see if it make an improvement. Maldo's car would the pretty much the same exact thing what your car is doing when going from like 60 to 85 MPH and now he said its about 80% better.

Hope that helps,
Claude

 

The plate IS on. However, I could be going as slow as 55-60 in 5th gear, hit the throttle, and get a vibrating, chugging sound as well as really no pick up. There's no hesitation, just no get up and go. Along with the vibration sound, it is loud and reverberates throughout the entire car. Next time I'm under the car I'll slide that ES bushing plate out. Thanks for the info, but I don't think that is what's causing this. How knows? I'll give it a try. It just seems to me that the car is bogging down and 'chugging' too much, at these speeds vs rpms.
Thanks

 

I really know absolutely nothing about the knock module, but I read in another thread that the module detects knock and is way too sensitive in the stock PCM. Maybe the vibration is setting off the knock module and retarding the timing. Dunno, but sounds like a must mod to me.


Knock Module Thread

 

I already have the LT4 KM. I don't know what's going on. This morning at 1800 rpms, 45 mph in 5th gear, REAL doggy and very LOUD reverberation in the car. However, real strong throughout the gears, NO HESTITATION. It seems that whenever I try to fix/upgrade something and think this car is totally good for the season, something comes up that bothers me and makes me frustrated that I don't even want to drive it. Drive from work is 26 miles, by the time I get close to home, this vibration,noise, and reverberation is REALLY BAD in all gears, all rpms. Help me.
Thanks

 

has it occured to me that yo could be bogging the engine.

giving it alot of gas in such a high gear, at lower rpms will make the engine work VERY hard to accelerate. kindda like starting off in 3rd...it doesn't like it.

i noticed that since i put my prothan trans bushing in, that if i let the rpms drop a bit too much, and the engine starts to struggle, that "sound" is transfered into the interior much more.

does it do anything like you describe if you use a lower gear?

giving too much throttle in a high gear is like starting on a bicycle in top gear...no matter how hard you push or how strong you are...it takes forever to get going

 

Yeh, your definitly right. But, after driving for about 30 minutes and the 26 miles, when pulling out from a stop, the vibration kills me, as well as the sound! None of these are present after only driving 5 minutes. What rpm should I normally cruise in, considering I've got 4:10's? I am wary of leaving it in 5th and cruising above 3000 rpms on the interstate. Just seems hard on the old girl. Thought maybe Y pipe is hitting, I just can't believe that though. Makes sense that maybe that boggy vibration is transmitting THAT much through the ES tranny mount. You think maybe my engine mounts could be worn through, and the vibration of the engine is going through the mounts to the whole car, like maybe when I am not letting it have enough rpm's when I hit it? Keep thinking maybe all this is in my head, but after the drive this morning, paying careful attention, I now firmly state this is getting re-god-dam-diculous.
Thanks

 

I had this exact same symptom when the TB intake elbow was ripped and not on tight.

CHeck for vacuum leaks. \