I put dyna-mat under the rear seat, and up the axle well behind the rear back rest, jute behind the devider board. much quiter inside the car now. There's still a very faint drone at 45, not obnoxious but I can tell it would be 100x worse with out the deadner

Manifolds
TTI 2.5"
X-pipe
Dynomax muffs

I have 1 7/8" TTIs and Dynomax Super turbos w/ 2.5"pipe. I was surprised to find that I had no drone. I to used dynamat but I have no idea whether that made the difference. Oh...and I do have an h-pipe.

i have headers plus a 3" TTi X.Pipe System with the long Dynomax Super Turbos. Cars is packed with Raamat and Ensolite foam. Everything is fine as long as i have at leas one side of windows shut. As sonn as i open all the windows i have a very bad drone – but only at idle speed (makes me hate stoplights)

Well, I'm not an acoustics engineer or any other kind of engineer, but it sounds like you have a passive radiator problem. In other words the panel or componenet that is vibrating is not being excited directly, but is just transmitting the vibrations.
Used to be a stereo speaker back in the 60s or 70s that use this idea to "enhance" bass frequencies.

What you have to do is add mass (undercoating, stick-on insulator, etc to the panel or item, or support it more ridgidly. Something to get the culprit's resonant frequency away from the exhaust system frequecny

The panel or componenet might be behind the headliner or unedr the carpets or in the trunk. Problem is to find it.

Or do what I did after my second set of glass-packs: ditch the duals and glasspacks and install stock single exhaust. Ahhhh peace and quiet....

I'd go for undercoating for sure.

My $0.02

Our Dakota had a horrible drone that vanished when the headers were increased from 5/8 to 3/4 primaries.

Maybe you can use larger diameter pipe between the manifolds and muffler? Drone is the most uncomfortable thing to endure, so good luck!

Are you using the factory muffler shield?? It should stop a lot of the noise before it hits the floor.

Oh yea, NEVER buy a Lil Red Express,cause there is some drone....

I have a super turbo on my V6 Dakota and it has an annoying drone over 50 mph.

My Fury has a healthy 440, TTI headers, 3" exhaust, no cross over and Cherry Bomb Vortex mufflers. I am told it is really loud when followed, it can be heard over a mile away! However it is very comfortable when driving, you can easily hold a conversation at 70 mph with the top up or down. The Vortex mufflers have a very low restriction, slightly curved follow path, but the case is super thick and solid. They have a deep, rich, mellow sound, but they heavy case seems to help funnel all the noise out the back, rather than up through the body. The only insulation in my car is the jute carpet padding.

I have experienced the same results when I used to have iron manifolds and 40" long glass packs. My brother used to have 24" packs on a Duster that was awful, I have had 36" and 40" packs on a couple vehicles with great sound and no drone or cackle.

I think the thicker cases help the drone a lot. i wouldn't use the Vortex on something I raced though, they are heavy, not will never rust out!

If you want a quiet exhaust--buy a Rolls Royce!
Someone is onto something in regards to the undercoating.Not only does it "protect" is also deadens any noise from the ehxaust.
But not everybody likes the look of its black ugliness-especially after all the hard work detailing the belly of the beast.
May I suggest installing dynamat or something similar under the carpet to quiet the cabin.
Nobody sees it,and you can still show the underside nice and purdy.Then run whatever exhaust you prefer.
Much easier and affordable than spending big bux and wasting time on swapping exhaust systems that will still be loud.

if your looking for a sound that you can legally get away with on a hot big block....4(2x2) mufflers reducing to 2x 2 1/2" or less outlets.

only way to get these machines quiet.

the resonator you tried meant glasspack, right? or was it just a tip? anyways install the glasspack before the muffler to get that benefit.

no 3" outlets. it opens up a new group of low harmonics that penetrate. its affecting people not even able to look at your car...thats kind of stupid.

didnt some magazine do a backpressure study and found that rear tailpipes account for some "measureable" forward thrust?

Insulate, insulate, then insulate some more... That's the best advice...I've got A/C so I added some thick jute carpet padding on the floor,roof, jute padding under the back seat and wheel well areas,on the package tray and rear divider as well as foil type behind the door panels...And I inadvertently quieted the whole seating area down dramatically... I've got Hooker 1 7/8 super comp headers and a complete TTI 3 inch "H" pipe{which is louder than the X}with the super turbos and there's no drone or resonance...You have to roll the windows down if you want to hear it loud...And it definitely sounds different to the people outside or behind the car on the road...

Won't all that insulation prohibit the shaped and properly contoured carpet from fitting properly?

I've got hooker 2 inch headers and 3 inch exhaust to the axel and 2 and 1/2 out the rear bumper on My 67 GTX.H pipe.(flowmasters 40,sounds great) 440 stroked and bored to 498. I have that damn drone at 45 to 70 mph ...not real bad..but there...if You figure it out..let Me know. I have zero floor insulation and will give that a shot. Thanks to all for their input

I fought your same problem with my 70 Challenger with the TTI 2.5 and manifolds, both with just the Dynomax and with resonators behind the dynomax.

my car has undercoating and I had lined the interior with sound deadening/heat blocker and from 2K to 2.5K I had a drone so bad my ears would ache all day after just a 20 min ride.


I finally changed everything to a stock style exhaust from Accurrate LTD and now it is a pleasure to drive.

Try this and tell how oh how you never did it before......

ADD RESONATORS!!!!!!!!!!!

Toss some GOOD resonators at the back, get rid of the drone. Add two more mufflers, get rid of the drone. Add Dynamat and try to mask the drone....

My 70 Challenger 451 has a complete TTI 2.5 system and headers and it only drones at idle. Interior is completely original stock.