Today I actually had the opportunity to drive my car on the freeway. With the 6-speed manual, I'm able to get the RPM's down to about 2000 while driving at 70 mph. I have one big problem with that... The drone is absolutely unbearable at high speeds. I ended up dropping my speed to 60 mph where I was cruising at 1500 RPM and the car was as quiet as a church mouse. My only other option was to speed up to 85 mph where the car was cruising at 2500+ RPM. While inspecting my engine bay during my lunch break, I also noticed a bigger problem, that my headers are resting directly on my steering box.

So, I need two fixes: 1) Is it possible to move/shim the steering box or engine so they won't contact anymore? (I have a cherry picker) 2) What's the best way to get rid of the drone?

My 408 makes about 523 hp. I have TTi shorty headers, TTI 2.5" X-pipe, Dynomax Super Turbo mufflers, and turn downs. I realize that the 2.5" diameter is undersized for the amount of peak horsepower I'm making, but I needed the 2.5" exhaust to ensure everything cleared the undercarriage.

Changing the muffler will probably be the easiest way to get rid of the drone, I just don't know what style of muffler to try to remedy it.

tail pipes will help A lot.

for sale 1968 Dart GT. then go buy a new challenger. All fixed

Thanks for the productive and informative response.

Hey Samy: (AKA Baller in training)

The interference may not be the direct cause of the drone but should be corrected anyway. Contact like that may cause vibrations at all times. I had an ear on a transmission crossmember rest against the trans mount and it buzzed at all times! The engine and trans, even when perfectly balanced, produce vibrations that certainly will find their way to you if they are not absorbed by something. The rubber in the mounts does this. This is also why the poly urethane mounts transmit more vibration.

I'd rather see the header clearanced (Dented) than to mess with altering the steering box position. The latter may result in increased bump steer, steering wheel off center, more turns to left than right. (Or vice-versa)

Hot Rod magazine did a dyno test where they tested an engine with new header,s then they bashed several tubes. The second test showed only a very slight loss in power. I took that to mean that one should not be afraid to put a few dings in their headers to get the clearance that you need. It sucks to ding up new pipes but life happens...

If you have turn down exhaust pipes in front of the rear axle, you will be amazed at how much quieter the car would be with full tailpipes that exit beyond the rear bumper by an inch or so. The under car exit causes the sound waves to resonate, reverberate and buzz the entire car.
I don't have any experience with the type of mufflers that you have. I ran Flowmasters for many years but changed to Dynomax welded Ultra Flo mufflers to eliminate the echo/reverberation. These Ultra Flos haxe zero drone at any rpm or road speed.
I know that you have spent a ton of $$$ and may be looking to save a few bucks. I know I would. You can try dimpling the header for clearance to see if it helps. I doubt that it will but it is needed anyway. Shoot for at least 1/4" clearance.

I know its a PITA to get in and do it. But sometimes you can loosen all of the motor mounts and lift the engines weight with the crane and then re-tighten everything. More than likely the mounts were bolted on and then dropped in. There is a small amount it can be moved by loosening them all and re-positioning it before tightening it down...
I'd venture to say by doing this you are going to make your oil filter clearance on the other side tighter....

The drone is typical without having tailpipes...

Tailpipes out the back will help a bunch. What do you have for motor mounts, is it a solid driver's side mount?

You can consider a pair of resonators as well.

Which 6th gear do you have, the 0.50?

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.

Sorry, my terminology seemed to have confused everyone. I have TTi's exhaust tips that turn down after the muffler.

Tailpipes will probably fix most of it, getting the header to steering box issue fixed will get more of it and if you do not have a crossover, either an H or X pipe that will help. Adding resonators will help. I'd do the first two then see if it's gone and add the rest in order of listing if needed.

Make sure the exhaust is rubber hung, the stock hangers were designed to isolate exhaust noise from the chassis, use them if you can. Gert under the car and very closely inspect the exhaust system for any other rubbing or metal to metal contact, do not be afraid to move the system about by hand to see if things can touch, even if it appears not to at rest.

Move the engine or dimple the tube before you fool with steering box location. Of course you ought to do a bumpsteer check to make sure the gear box is in optimal location before you move or dimple, but it's not 100% necessary, just attention to details there.

Another vote for tailpipes.

If you do go with tailpipes and they don't eliminate enough of the drone by themselves, then any cheap bullets (we used to call them glasspacks) in the tailpipes work good as resonators and usually deal with the remaining drone quite well. Do you have room for all that?

You should try to re-position your engine as suggested above. But it looks like you are probably going to need to hammer on your headers. That won't hurt your performance, but will take a toll on the coating.

A piece of insulation there will help to cover up the dent and the accompanying coating damage as well as keep a bit of heat off the box.

I have the standard 67-72 motor mounts. The biscuit style I believe so there seems to be some wiggle room. I have to see how much room I have for resonators. And my final drive ratio for the trans is 0.63:1. I'm running 3.55 gears on a 26" tall tire. But doing the math, I may have the other transmission, which I hope not.

Do you have tail pipes at all or just dumps at the axle ?

Schumacher sells shims that go between the biscuit and the K frame , but don't get carried away and change your drive shaft angle , I would try shifting the engine toward the passenger side instead of raising it because it could eventually settle back down.


Also you could grind a little off the steering box ... that is obviously more work ...

I have full tailpipes with their exhaust tips. The exhaust dumps before the bumper.

That's what I was worried about with changing engine position. I'll probably try skicker's method tomorrow and moving the engine a little to the passenger side. I may even dent the header. I have a feeling that contact may be causing part of my drone. I have the day off tomorrow, so I have some time.

tailpipes for sure. I tried various mufflers and turn downs on my Fury before finally putting the tail pipes on. World of difference.

And dent the header and be done with it.

My TTI 3" system does the same thing. I think resonators between the axle and bumper are where we are headed...

I was thinking of a decent place of putting them, but there's hardly a straight piece of tubing on the entire system. If resonators are going on, they're probably going to have to go there.

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.

I wouldn't worry about denting that tube, you might be able to use a long pry bar with a rag to pinch it there. Otherwise you have to mark it, and either remove it or jack the engine to be able to actually swing at it with something. Usually scratching some paint or injuring yourself...

Nice! I have a guy here that is going to do some for mine as well. Do they work?