Hey whatsup fellas, been a while since Ive been on this board... maybe I can get some answers from some of you seasoned veterans

My true duals (and every other LT1 I have seen with duals) has a horrible drone to it right at the range where you cruise on the freeway. Is there any way to get rid of it? My system is exactly like kmook's old system, Hooker LTs to 3" Heddman xpipe to 3" bullets and turndowns at a 45 degree angle with the ground. It's loud as **** and I love the sound, but the drone is unbareable...

What will get rid of it, it seems like a problem inherent to running true duals with the exhaust pulses specific to the LT1 motor. Anybody succesfully get rid of it???

 

You might try a different style muffler, that could help, possibly a turbo one or chambered. A fiberglass packed bullet kind of has that always there tone, it doesn't "pulse" like an ordinary muffler, that could be part of the problem. There's mufflers out there that are about as deep as a bullet so you can still fit it under there.

And I have heard an X-pipe has a certain amount of resonance to it that can't be eliminated. After all, in equaling out the exhaust pulses, you're going to make it sound more "even" and it will have less of a pulsated or "rumpity-rump" sound that SBCs are famous for.

Basically, if you want to mellow it out a little bit, you might lose a few hp in the process, but as usual, there are sacrafices you have to make if you want performance, and if you want a loud exhaust, you're going to get some noise on the freeway.

Hope my suggestions help. I've listened to several x-pipe/bullet style LT1s now and I think I still prefer LTs w/ separated duals and some chambered mufflers. I think I might end up going with an H-pipe as a compromise between regular and x. Has anyone even done that on an LT1? It woluld be nice to hear a clip before I buy. The X-pipe thing is so popular right now everyone seems to have forgotten there are other options still.

 

Hwat gears do you have in the rearend? A friend of mine changed over to 4.10s and due to the higher rpm his drone went away, and he got better gas mileage because the engine was i better rpms for his power band, Just my 2 cents

 

It's the turndowns. No doubt. Take the bishes off.

 

Based strictly on anecdotal evidence, the #1 cause of drone seems to be the selection of too large an exhaust pipe size. That's also bad for scavenging, since overly large pipes also cause you to lose exhaust velocity, which is bad for scavenging.

You mentioned that you have the same exact system as Kmook.
If you're engine doesn't have pretty close to the same power levels as his, you have too large an exhaust system. On a dual exhaust for an LT1 at stock displacement and typical street power levels you probably want no more than a 2.5" pipe. Anything under 300hp and you probably want to at least consider 2.25" pipes.

 

Here's the main drone issue... it's dumping underneath the car... plain and simple... get the tips out from under the car, and the drone is gone...

I've had TDs on my car for 2 summers, and with it exiting infront of the rear wheels, I have ZERO drone from my exhaust.

With dumping under the car, you are resonanting all the body panels on the bottom of the car, thus the drone; dump the exhaust out from under the car, and no more drone, that simple.

 

Yeah, like everyone has said, either exit the true duals out the back or out the side, NOT under the car, thats where the problems are at.

 

I had a MAC catback system that droned unbearably. I fixed it by cutting the resonators off. The tone became more aggressive and a bit louder, but there is no drone. My thinking is that you just need to alter the frequency of the sound waves in some way or another.

 

Haha. Well i had a set on my SS, It was not that bad but it did have a large cam in it. I now have a set on my TA and the drone is much worse... and it has a stock cam.

For one i think having a cam makes a difference, at least in my definition of drone. Second i'd agree with everyone else on the turn downs. Maybe change the angle of the turn down, or just make them point almost straight back? That might change the amount or at least pitch of the drone.

 

I've got 3 inch true duals dumped. He's right there isn't really any reason to go bigger then 2.5 inch unless your running a sick 383 or a power adder. I'm putting down about 350-360rwhp and i dont need the 3 inch. If i could do it all over again i would but i guess it leaves room for improvement right....

 

My bullets just flow straight out towards the back of the car. Sounds 50x better.

 

Yes, fix your turndowns. mine were turned like yours at first, and I had horrible resonance, but i cut the majority of the turndown off, and had them exiting almost straight out the muffler and it sounds soooo much better.
Heres a link to the way mine look.
My True Duals (LS1)

 

Do you just leave one cutout open at a time?

 

Nah, that was on that pic was taken on the lift when I had my cutouts welded on.

 

The problem is your tips are angled towards the ground so the sound reflects off the ground and resonates back in the cabin.

Turn the tips so they are sideways instead of facing the ground.