Eric at Classic Chambered Exhaust made me a set of these 2.5" resonators to fit beside the gas tank on my 70 Challenger. He made them so that they would bolt onto my new 2.5" R/T exhaust tips. All I had to do is cut off the rear TTi exhaust pipe and clamp them on.

My car with the same exhaust system other than having long tubes (and Ultra-Flos which should be worse than super turbos) had more drone noticeable with the TTI turn-downs on it. I eventually cut them off and went with some tips that stick about an inch past the bumper and its a lot more bearable. I think those TTI turndowns cause some "drumming" under the car.

Could you temporarily try taking the turn down tips off just to see if they are causing it?

I once had a car with full length exhaust exiting into exhaust tips that ran parallel with the ground exiting under the rear valance and never had a drone issue at any rpm. It had Hooker Aero Chambers and 2.5" pipe start to finish.

Very cool. What was the change in loudness and drone?

On A-bodies with full exhaust the leaf spring and gas tank barely fit 2 1/2" exhaust. So can go any wider than that. Can go up and downward for a box or oval type deal with the same width as the inlet and outlet diameters. Never seen a 2 1/2" resonator like that.

Are those really TTI shorty Headers? The first tube seem to drop down instead of angling back at around 45 degrees.

They're TTi's...

Can you undo the motor mount and jack the engine a little to get some room to make the dent? Otherwise mark it and unbolt it. You could possibly move it enough to dent it?

Yea they are, most TTI shorties I have looked at had lots of space around the box. Even the stock power box clears no problem. Did you use old rubber biscuit engine mounts that may have flattened out over time?

The length of your tailpipe from muffler back matters a lot to the rpm where Drone is most severe. Just as a Church Organ makes different musical notes when different length pipes get air blown through them, so will your exhaust make annoying music.

Very roughly, if drone was severe at 2000 rpm, and much less at 1500 rpm,
then your tailpipe length needs to increase
2000 divided by 1500
4/3 rds

Other things come into play here, such as the temperature of the exhaust gas, which will be higher the more the trottle is opened.

You could experiment to find the added length that snuffs out drone.
Buy two ninety degree fittings, and two lengths of either solid or flexible corrigated pipe,
and add maximum length for side outlet style exhaust,
then cut off about two inches at a time untill the exhaust note suits you.

Drive up steep hills to demonstrate how a more open throttle changes exhaust temperature and therefore drone.

The quietest set up for low drone in the 1200 to 2200 rpm range is usually large "Helmhertz Trap" mufflers mounted cross ways near the rear bumper fed by as long as possible tailpipes. T-Traps of closed stub pipes the right length can also kill drone at a particular rpm.

Really well stated. Furthermore, the tub of your unibody car is one big musical instrument as well. When the mufflers resonate, all that harmonic vibration will make the car itself drone. In fact, much of what you're hearing is the car! If you haven't gone the dynamat route this will help a bit but not completely. The last car that I installed dumps on was longer ago than I'd like to say. I found a great solution for the drone. I purchased a pair of Thrush resonators and installed them after my mufflers and added about a foot of pipe beyond them so the dumps dropped right in front of the rear axle and it completely solve my problem. Before I installed the resonators, the drone was unbearable like yours at a certain RPM. Second gear was a real beotch. Just remember that the harmonics of every exhaust system are different, so what worked for me may not work for you.

If you want to see how harmonics work go inside a walking tunnel of decent length with smooth surfaces. Stand in the middle. Then start singing a low note and start raising the pitch. At some point your voice will begin to make the tunnel start ringing really loud!

If the header tube is just barely touching the steering box and there are no sharp spots to wear thru the header tube I would just leave it alone.

My dad has an early nova and the steering link touches the headers at full lock. While it has left some small witness marks on the headers it's not enough to justify wrecking the ceramic coating by beating dents in them for that last 1/16" - 1/8" of space.

Do you have a spare tire and rubber trunk mat? If not that may help as well.

I'm quite suprised as well as I know of a couple of people who have both the Borgeson box and TTi headers. But with how wishy washy factory tolerances and 40+ years of moving around anything is possible.


That's quite possible as I reused the ones that the previous owner gave me.