Exhaust Interference and Drone Problems

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?

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.

I ran a full TTI system in a 68 Barracuda the super turbos drone like crazy. I now have Ultra flows much better also tail pipes are a must.

I will try that soon. Tomorrow I should have some time to play with the car and it shouldn't be raining. I'm going to start by attempting to dent the header as that needs to be done regardless. Afterwards I'll take a look at the tips. IIRC, they should only be held on by exhaust clamps, if they're welded on, I may just go with some circular resonator past the muffler.

I was thinking something like this may work. They don't look that much larger in diameter, but I'll have to take a better look:

https://www.summitracing.com/parts/vpe-1792/overview/

https://www.summitracing.com/parts/sle-310013919/overview/

They're TTi's...

So, I just took a look at the headers, and I don't know how I'm going to be able to dent these while they're still in the car. I have some flat ended punches and I can barely fit them around there. Even with a rag on the other side, I'm worried about puncturing a tube or something as I gave them some slight hits and knicked the surface of the tubing.

As for the exhaust, the tips seem to go from the mufflers to the back of the car. So any modification will require some welding... Speaking of which, I just got a cheap flux core MIG welder for Christmas. However, I won't tackle that as my first project.

Looking at the underside, I have some room between the leaf spring and the gas tank. My exhaust is actually a lot closer to my leaf springs than it is to my tank. But if I go to the resonator route, there's plenty of space past the gas tank to mount them.

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?

I'll fiddle with it tomorrow. I have a cherry picker and some lifting chains I can try for the first time.

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.

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!

Well, I'm having trouble with denting the headers. I tend to be a wuss when it comes to hitting things as sometimes I don't know my own strength and may break something if I try to hard. How hard can I hit this thing? Right now I'm using a punch with a flat end on it (microfiber wrapped around the edge) and a hammer. This is all inside the car as I just realized the headers don't have hex-head bolts but the 12-point or sided bolt (I don't remember what they're called) and I don't have those sockets on hand (another thing for the wish list). My last resort is to undo the motor mounts and move the engine.

As of now, I have no sound deadening in the car. I wanted to lay some in the back for the electric fuel pump as that can get very noisy. But since the car is so stiff, the vibration is just circulating everywhere as it's trying to find something to give. 6th gear is unbeable between 65-80 mph (optimal CA cruising speeds). The magnitude of the drone is less at lower speeds.

The problem is that the TTi system uses offset mufflers so I'm going to need my resonators behind the rear axle. There's plenty of room after the gas tank, but how much room after the resonators do you generally need before dumping the exhaust? Can you do it at the resonator outlet? A couple inches? I don't think I have enough room for a 12-18" resonator and another 12" of tubing.

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 might at this point, but we'll see. The side of the header contacts the round body of the steering box.

I need to measure/find a spare wheel for this car as I've got the big brakes up front. But it's in the works. No rubber mat either.

How about using a large flat bladed screwdriver or stock type lug wrench flat tapered end to push in between the header tube and steering box and used that to push it in a little

I would fix the engine mount before you start bashing the header, if you have looked at other cars with the same headers and box you already know that you should have lots of clearance in that area. I guess that whoever put the engine in just bolted it in wherever it landed in the engine bay....

I could try that. Maybe later in the week.



I actually read in another thread that someone else is having problems with the TTi shorties and Borgeson box. I'm curious if the '67-72 K-frame vs. 73+ K-frame makes a difference.

I would just dump directly out of the resonators. If you go over the axle you're achieving the same effect that 360view was referring to by adding pipe. No guarantees, but it's really the best you can do.

I kind of like that idea.

For denting the tube in just the right way, perhaps a hydraulic c-clamp or similar?

Headers are always a pain with fitment. TTI uses good tubing that is hard to dent. I was initially thinking that you could use a long pry bar in between the area there as well. If it's not transferring vibration into the column or making noise, I would just let it clearance itself.

Plus you don't want to chance cracking the steering box while you are trying to dent the header.

Whats wrong with a few shims between the mount and bracket?

While were talking about noises from the back of the car check to see if the trunk lid torsion bars have a rubber sleeve between them where they crisscross in the middle. If the rubber is missing the bars can rattle against each other.

I don't think the trunk torsion bars could create the exhaust drone, but you may as well add the rubber if you don't have it. A couple inches of fuel line with a slit down the side of it will duplicate the original just fine.

I'll leave it alone for now and probably add resonators to the back in the future.

I have the Vibrant SS 18" Bottle Resonators on mine, and it really makes a difference.

Mark

Same here with the short case super turbos on my big block Dart , I think it's the mufflers , the rest of my system is factory manifolds and mandrel bent tubes front to back.

Have you tried moving the engine to the passenger side some yet ?

I see you have a Borgensen box , TTi makes the headers to fit with a Chrysler box , is the Borgensen that much bigger in that area ?

Don't try to dent the header with a punch, that is not going to work, especially with the header on the engine and in the car.

If shifting the engine over doesn't get you some room I think you should just bite the bullet and pull the header out , dent it , and put it back.

As far as the drone it's those short case mufflers, put on an ultra flo and see if it changes it .

I have those TTi tailpipes, I'm still trying to figure out what the bleep was going thru TTi's mind when they came up with that mess. I cut mine all up to get them in the FACTORY location, total waste of money .

Bringing this thread back from the dead. I have to make this car more road trip/gf bearable. Gf loves the car, but it's pretty annoying that we have to raise our voice in the car to talk cruising around town. I haven't even taken her on the freeway, yet.

Since the last post I had, the 14" Dynomax Super Flow mufflers were removed and 18" Magnaflow mufflers were placed in instead. This removed some of the drone, but not all. Now it only drones between 1800-2100 RPM, but is still pretty bad and in optimal cruising speeds. I also had the leaf springs moved in with Dr Diff's offset shackle kit so adding resonators to the tailpipes may be a no go at this point. I'll have to check tomorrow (finally, a day off). That being said, in December, I'm going to have a 3 week break from my master's program and the last week of the year, I'm taking off from work, so I'll have some time to work on the car. I am thinking about going with some advice most of you had in the beginning and getting rid of the turndown tailpipes and adding some clamp on exhaust tips to, hopefully, redirect the pulses away from the car instead of under the car. I can only imagine it should be pretty easy and only require grinding the tips off, deburring the tubes, and clamping new ones on. Once I have time to play with my el cheapo welder and be comfortable with it, I'll weld them in place in the future. I was thinking about either dual (https://www.summitracing.com/int/parts/jex-jst123/overview/) or oval tips (https://www.summitracing.com/int/parts/bor-20155/overview/), but am not sure which would look better. I want something a little different than classic round tips. Does anybody know if these usually come with clamps or if I should order some? If so, what's the best clamp to get?

If this doesn't work, I may just follow 360view's advice and try clamping on 90's and making it sort of like a side exit exhaust from the back to get rid of that drone.

I'm looking to order parts soon, so I can just have at it once I finally get my break.

Any advice would be appreciated. Thank you all and Happy Thanksgiving!

I hope you can deal with your drone with the changes you are making. But my personal experience with this is that nothing will kill the drone other than some sort of after-axle resonator.

If you find an alternate fix, be sure to let us know.

Running the exhaust out to the bumper will be a big help. I had turn downs in front of the diff on my Duster that got to be annoying with the sound resonance later on. Sounded cool at first but not later.

There's a big difference between running turndowns in front of the rear axle and running pipes out to the bumper. But if your tailpipes run to the back bumper and end in turndowns, changing the shape of the last 3" isn't going to change a thing.

One thing to think about is the floor is like a big speaker. You can reduce sound levels a lot by damping this area. There are many choices such as Dynamat, Fatmat, Lizardskin, and asphalt roofing material. I don't fancy my car smelling like the La Brea tar pits on a hot day, so the roofing material is out for me.

The trunk floor is another prime candidate. Then there is the hood and firewall. Lizardskin is applied by spraying so for the trunk and under hood areas it might be best.
You may not want to be spraying in your car interior so one of the peel and stick products would be more readably utilized. Reading the websites I see there is more to the stuff than simple mass loading, which is what the asphalt roofing material does.

Here's an experiment for you: there are a lot of flooring products that come in one foot squares and are peel and stick. You cold run an experiment for just a few dollars. Apply the flooring material to your interior floor and trunk floor. See if it makes a difference. It won't cost a lot as I've bought squares at one of the dollar stores for a dollar a square foot.

I didn't read all the posts so I cant remember if you have an H or X pipe already. If you don't have one, get one in there.

The bullet resonators will also have a great effect on sound. Back in the day there was something called "chambered exhaust" Where the exhaust pipe was deformed so it acted like a muffler. I wonder if anyone has aomething like that to act as a resonator and not take up so much space.

Oh, and nice Dart! It looks super smooth and clean.

Good Luck,
R.

Then there's sound cancelling technology.........

We'll see how it turns out. I have never been a huge fan of the turndowns so getting regular or dual exhaust tips will be a visual more pleasing to me and probably worth the investment. Again, I can add length to the back if I add a 90 degree bend an extend it to a "side exit" exhaust and if that doesn't work, then I'll have enough room for resonators.

Yeah, when I took my car to the shop last, I gave them some dynamat and told them to install it in the cabin and they never did so I still have some left over. For now, I just really don't want to start taking out the interior. Who knows, that may change once I have that week off.

Just walked to the garage and measured things out. Resonators are definitely not going on the tailpipes next to the leaf springs. There will be interference. With just tips alone, it seems like I will only extend the exhaust by 2 inches, so like some of you said, it may not do much.

My other option is doing a rear-side exit exhaust which will definitely be interesting. Either I could just extend the exhaust to the side with a 45-90 degree bend capping it off with exhaust tips or I may have enough room to reroute the exhaust off with just a 60-90 degree bend and a resonator (Either Jones Exhaust - https://www.summitracing.com/int/parts/jex-jr25/overview/ or Vibrant Performance https://www.summitracing.com/int/parts/vpe-1792/overview/). If I go to the resonator route, I will probably just have the "cannon" look as I won't have enough room for exhaust tips. Not sure how that will change the sound but hopefully it eliminates drone.

What exhaust clamps do you recommend? I take it these are for pipe-to-mufflers/resonators (https://www.summitracing.com/int/parts/pye-hvc10/overview/) and these are for pipe-to-pipe (https://www.summitracing.com/int/parts/pye-hvc65/overview/).

http://www.accurateltd.com/Hi-Po-Resonator-Tip-Assembly_p_267.html

How long is it and what kind of clamp would be required?

Are you running a crossover up front? (an H-pipe or an X-pipe)? If not, that will help. Do you have room in front of the mufflers for some resonators?

what is the smallest out side diameter resonator for 2 1/2" pipe? These are so low there's scrapage from high centering on speed bumps and driveways.

A couple of the older posts alluded to these but you seem to have missed what they were talking about - Terms for the same thing: Helmholtz resonator, 1/4 Wave resonator, Branch Resonator
Google Branch Resonator and the flick to the images results to get the idea
This page has some technical ways to work out lengths
http://mkiv.supras.org.nz/articles/exhaust_drone.htm

You could possibly fit a pair above the diff?

With some creativity you could make them adjustable fairly easily

I'm already running an X-pipe and there really isn't any room in the front for a resonator. That was the first thing I mentioned to the muffler guy when I brought the car in.The exhaust is too close to the body and transmission. Heck, I'm even rubbing in a couple of spots. Anyway, the diameter of the smallest resonators that I could find was 4" as shown in my links above.

And I have high centered the car on a speed bump in my work parking lot before, but since then I've raised the car in the front about 1/4-1/2" and added stiffer springs.

I saw them, and it's a cool idea I would like to implement, but that would require welding and that's a skill I am not comfortable with just yet.

I'd ask Accurate, I do not know, but I do know it's a reproduction of the factory setup, so it "should" work in that area

Did a quick search and it seems that some Chevelles and Mustangs came with a muffler before the axle and a resonator out back from the factory.

I can build 2.5" core resonators with 3.5" OD bodies in any length (well - as long as 40" body). As far as the dead-end tuning pipes & bullwinkle pipes, I've NEVER seen someone actually run these on any application.

So did a butt ton of Mopars

The early A body 273 hipo setup was like that

What is keeping you from fixing the rubbing? Touching exhaust can make an enormous amount of noise.

The header was rubbing against the PS box and the exhaust pipe was hitting the T-bar. Since then I got new T-bars and I haven't looked at it. I am more timid working on the front of the car than the rear. Just dealing with more weight (engine). I never feel comfortable working with it alone.

We are heading into the colder seasons of the the year.
Does your vehicle's Drone noise change with air temperature?

I have been toying with the idea that the RPM and throttle setting where drone occurs could be shifted by injecting air into the exhaust with a 12 volt compressor. Water injection might work also.

Cooler exhaust gas should have a lower speed of sound,
which should shift the conditions where the Drone is loudest.

Someone adventurous might also experiment with adding E85 to the fuel.

The most recent night when I brought it home, it was about 50-60 degrees outside which is usually about 30 degrees cooler than when I normally drive it. I did not notice a change in drone tone or location. The drone almost always occurs between 1800-2100 RPM while I'm inputting some sort of throttle.

If it's rubbing it will always make a drone. Fix that first

Well, then I'll need to move the engine. As mentioned at the start of this thread, the headers are hitting on the driver's side. I checked the Torsion bar interference and it seemed like the mechanic dimpled the tubing before installing the T-bar, but there is still a small amount of rub. So, my engine needs to go a little up and to the passenger side which should be accommodated by a shim

What's the safest way to shift the over to the passenger side with shims and what tools will I require? I have an engine hoist and quite a few different chains/tools for lifting the engine I bought from Summit when I got the hoist. Is it as easy as loosening up the motor mounts and installing some shims? Schumacher seems to be out, but I may have some extra scrap metal lying around. If not, would washers work? Do they go between the bracket and the rubber mount or between the K-frame and the rubber mount.

OMG, are you kidding me? You would go through all that to reduce or eliminate exhaust drone/resonance? CHANGE THE MUFFLERS or add resonators to the current setup! For the love of God!

Some of the cheapo parts store biscuits are quite a bit thinner than factory. And of a lower quality. Replacing them with the proper thickness may move your header away from the box. You could easily make some shims to put between the biscuits and the k member. All you need is some flat metal, a cut off wheel and a drill. Personally, I wouldn't trust the cheap rubber mounts as far as I could throw them. I prefer solid mounts as I don't mind a little vibration. There are alternatives though : http://www.dodgecharger.com/forum/index.php/topic,13216.0.html

Schumacher usually shows where the engine should be located, i.e. it's factory location. I would confirm that first, then if you can move and/or shim things about till all clears. But it is not uncommon, even with TTI's to occasionally need to manually clearance the tubes (bash a dent in them). If you decide you need to go that route I'd look at how some do it with finesse, You tube video or similar.

I'll take a look at my biscuit mounts, They're probably a little worn out as they were on the previous owner's engine. I think I have some 1/8" steel plate laying around and I have a cut off wheel and plenty of drills so that shouldn't be a problem.



I found the engine location guide per TTi's website. I'd rather not pursue the dent the header route as it has more manual labor involved, but we'll see what happens.

I am not sure of whether God loves, tolerates or dislikes drone.

Ooommm.....

God gave us free choice, of course he dislikes drones

For God so loved the world he gave Mopars their beloved exhaust tone, that whoever doesn't have drone, shall not perish, but have eternal smiles.

Should take about an hour at most to drop a driver's side TTI header, at least it would in an ebody[?]. Drop it, press/bang it and go back together. The engine will move quite a bit on those mounts, you need sufficient clearance in a static and dynamic running state....FWIW i have a chromoly torque strap on my engine [which doesn't help NVH], the same transmission and zero drone. It's not much of a mystery, keep it from rubbing and put some decent mufflers on it.

IMO, if you aren't already, I suggest you take just a couple of trusted Moparts opinions and use them as your guidance. You can go round-and-round chasing rabbits within a large thread like this....

Things are pretty tight in an A-body. Even with a small block. But based of all of the information from this thread, I think this will be my plan of attack for my break.

1) Attempt to remove header and dimple.
2) If 1) fails, shim engine.
3) If 2) fails add resonators out back.

Taking a look at the engine bay, I feel more confident now.

Quick question. Is it worth it to replace my biscuits? The passenger side looks smooshed, kinda? If I do, should I go rubber, solid steel, or poly locks?

Someone else may need to confirm, but both mounts look out of alignment? They look to be rotated around a couple degrees????

my old eyeballs aren't very good any more, but those rubber mounts are not installed as they should be. they are to be in line with the block mounts, not having part of them angled off the K member pads. are they upside down perhaps ? there should be a "bump" of sorts that will locate the isolator in the block mount properly. am i seeing this correctly ? is this even the correct K member ? when i perform a transplant and don't have the correct K, i bolt engine and transmission together, locating the assembly with the transmission mount. then fabricate "towers" that will position the engine where it wants/needs to be on the K, after removing the original "towers" from the K before lowering the engine/transmission assembly into place.

This comes down to three common problems which require very simple basic fixes.

First, dimple the headers so there is ample clearance between the headers and the chassis.

Second, re-adjust the rest of the exhaust so nothing touches the chassis.

Third, add resonators near where the exhaust exits the car (parallel to the gas tank is the preferred location).

These three fixes will take care of your drone problem, period.

I had a drone on my 6.1 Hemi '69 Cuda with full 2.5" TTI H Pipe exhaust and Dynomax Super Turbo mufflers. Plus the exhaust was quite loud when cruising.
I installed a set of Flowmaster Resonators 15150S. Drone completely gone and exhaust much quieter. Very happy.
These resonators are a straight through 2.5" design with a closed tube alongside. Photos in this FABO thread http://www.forabodiesonly.com/mopar/threads/srt8cuda-build.218445/page-27
Jim

Cheeper way to go....

https://www.ruggedradios.com/index.php?main_page=product_info&cPath=111_22&products_id=17

The way your tailpipes snake around the spring and gas tank makes me think your best resonator location is in front of the gas tank. Looks like only a total of 120 degrees of bend added to each pipe.

Running pipes out the side in front of rear tires is much noisier than running out past the bumper.
R.

That's what I was thinking as they looked funky. Since I have to fiddle with them anyway, shouldn't I just replace them? Which motor mount biscuits should I use? Rubber ones are $5-15, steel is about $50 (but I feel it will cause too much vibration), and the poly-locs are about $200. Are the poly-locs worth it?



I can't. The mufflers are there and the X-pipe before that, and the trans cross-member gets in the way before that. I was planning on routing my "side exit" (angle exit?) exhaust behind the rear tires as that's the only room I have, if I go that route.

Motor mounts - I'd replace them if they look bad, but other than that I'd just get them lined back up. I have a set of small block mounts and they have a little bump on the mount that rides in a hole drilled into the motor mount brackets to keep everything pointed in the right direction. You may have the same thing as I do only yours got tightened down with the nubs out of the holes which is how yours went sideways.

Your car has a manual transmission so you'll want a torque strap or something to help secure the drive's side as that's where the action is. You can buy one, make, one, or overhaul your rubber driver's side mount and convert it to a solid mount with some steel and welding.

I would get the mounts straightened out one side at a time and work with shims and see what happens there first before messing with denting the header right away. If you do have to dimple the header tube you'll want to dust some silver header paint over the spot to keep it from rusting. In my mind having a header tube just barely touching the steering box is not the source of your drone sound. I think that is coming from the mufflers on back and is magnified by having an empty trunk compartment.

If you want to switch to side exit exhaust then look at the Dr Gas NASCAR style mufflers/exhaust tips. I think they would be fairly loud compared to rear exiting, but they may not drone. They are pricey, but offer the best look for that type of exhaust setup. Having a round pipe sticking out in front of the rear tire doesn't look very cool in my book.

https://www.youtube.com/watch?v=jucWtepx6PU

Alright, I can deal with that. So, as far as the mounts go, look for cracking in the rubber?

Thank you for the tips on repositioning the engine and possibly denting the headers.

I wasn't planning on doing a side exit exhaust in front of the rear tires. If moving the engine away from the PS box does not help, the plan was going to add resonators to the tailpipes. My problem is that I only have 11" between the exhaust hangers and the bumpers while the smallest resonators I could find are 14" long (10" long case). There are smaller "race" mufflers I can add that are 12" long (8" long case), but that's going to cost me a lot more per muffler than the resonators were. So, I was thinking about cutting the tailpipes off after the exhaust hanger, band clamping some 60 degree tubing, then adding (band clamps again) resonators so I'll have enough room to fit it all under the back of the car. The exhaust will still exit the rear at the bumper, but at a 60 degree angle pointing out. Or, I could do the same with 90 degree tubing and end at the back of the quarter panel. It may look a little funny though, but it will be different.

Next time you drive it you should fill the trunk with some blankets and sleeping bags and maybe a spare tire if you don't have one in there. I'd just be curious to see if the sound was reduced any amount by having stuff back there vs empty. Also there is a seat divider panel that goes between the rear seat and the cross bracing under the package tray in case you don't have one.

I have a suitcase with tools in the spare tire well right now, and I didn't really pay attention to see if it was better or worse.

I already have a divider. It's made out of the speaker box foam board stuff and I already put some dynamat on the back as I thought it was acting like a drum.

Very good practical idea to fill up the trunk volume. Ideal fill would be foam pillows from furniture, sleeping bad pads, folded beach towells, etc.

A quick test of whether metal to metal contact of the exhaust pipes is influencing the drone noise would be to buy some inexpensive high temperature rated, but flexible Silicone cookware pans, cut it up into small spacer pads, insert these pads into tight areas, and hold in place with those stainless steel cable ties.

A quick cheap test to see if a bit longer muffler would reduce the drone would be to insert a socket into the end of the exhaust pipe and temporarily hold it in place with a vice grip. This creates some additional back pressure that can be adjusted by changing socket size.

So, I untightened the bolt under the driver's side biscuit on the K-frame and put a jack under the engine and lifted it a bit. I found some scrap metal that was about 0.150" thick and cut out two 0.25"x0.25" squares with a 9/16" hole in the middle. I then used my angle grinder and slotted them. I threw one in and that was enough to move the headers away from the gearbox. I'm debating about throwing in the second for extra room (possibly between the exhaust and the T-bar on the driver side), but part of me wants to paint them before completely installing them.

Good that you were able to get clearance without denting the header tube.

Paint your shim tonight and install tomorrow? As long as you have clearance you may not need to do any more. Just keep an eye on it and if it sags back down add another shim if need be.

I painted them already, they're pretty dry. I may just throw them in tonight and tomorrow morning I'll go for a test drive to see if there is less vibration or drone.

I just installed the spacers and went for a 25 mile cruise. Overall, I think the biggest improvement is that it seems like there are less vibrations in the car and because of that it seems like the overall volume inside the cab has gone down and that there's a little less drone; however, the drone is still there. It was also hard to judge as it took awhile for the engine to warm up (it was about 50F today). Most of the ride I was under 180F water temp but I did notice that the hotter the engine got, the more the car droned. I think the next step will be resonators before the mufflers.

Good cheap progress!

Ok, looking under the car, resonators may not work as most I see are at least 4" in diameter. If anything, maybe a glasspack muffler, but it's going to be super tight to the floor. I've got about 2" between the centerline of the tube and the floor. The smallest diameter glass pack I'm seeing is 3.5". However, I do have 20" between the X-pipe and my mufflers.

Maybe something like this?
https://www.summitracing.com/int/parts/jex-a3516b-8/overview/

It's either this or possibly putting tiny mufflers out back, but those are usually chambered mufflers. There is a tiny glasspack, but I'm not a huge fan of the red.

https://www.summitracing.com/int/parts/sum-630853/overview/

https://www.summitracing.com/int/parts/jex-fb426/overview/

https://www.summitracing.com/int/parts/sum-630142/overview/

what ever you choose, make sure the internal core is the same size as the inlet/outlet nipples. the cheapies just use a 2" or so core with the bigger size nipples added to the "basic size" body.

I had Full length TTI headers with Dynomax Ultra Flows and full length 2-1/2" tail pipes on my 440 Cuda, and I did not have any drone at all. maybe tail pipes will help.

A little off topic but I'm curious how close your headers actually are to your steering box and whether you have any issues with power steering fluid temps.

- EM

Well, it's not touching anymore so it probably got cooler.

I talked to my dad and he said as a Christmas present he'd pay for an exhaust shop to throw resonators on the car, so I'm going to take it to a shop sometime this week to check it out and get a professional opinion.

Our exhaust systems are fairly different as I have shorty (unequal length) headers, a shorter wheelbase car, and different length exhaust tubing with a different engine. I don't think it can be fairly comparable car-to-car.

You said earlier that you were going to put stock style tips on it. You might want to cut off those turn downs that end 3" before the bumper and install the tips out past the bumper like stock before going the resonator route. You might be surprised with the results.

I just called the exhaust shop that had great reviews on Yelp. It was a one-man shop, but basically he told me that my car is going to drone and there isn't much he can do about it. He said I'd need a muffler that has both packing material and chambers to break up the exhaust while quieting it. He said he's worked on a couple of Dodge Darts and there's no room in front of the mufflers for him to put anything, as I suspected with my 2" between the centerline of the tube and the floor pan. I asked him if there was anything we could do on the tailpipe end like adding a glasspack, chambered muffler, or resonator and he said that odds are all it will do is quiet the car down.

I asked him about the turndowns too and his response was, "Resonance is resonance." So, I'm not sure if I should get another opinion or take all of the knowedge I've gathered from this thread and try something.

I think my next step may be to grab all of my blankets, like mentioned before, shoving them in the trunk, and seeing if maybe that will help as he hasn't had any experience with sound deadening.

The blankets in the trunk is a worthwhile experiment.
So is silicone caulking cracks that might vibrate, or filling voids made of flimsy sheet metal.

Another worthwhile experiment is to use Vice-Grips to clamp different sized sockets inside the exhaust pipes at the outlet. This slightly increases the back-pressure and changes the speed of sound in the exhaust gas.

You already mentioned you can hear a difference in the drone was the engine coolant temp went up. That is also a speed of sound in hotter gas effect.

The pictures you have posted seem to show you have room to add closed end T- stubs. These are typically 26 to 18 inches long. Think of these as “blind alleys” the sound wave charges down, hits its head on the closed end, and dies. Start long and trim off length until the sound cancellation is greatest at your cruise RPM. The stub tubes can be bent, even coiled. They can also be the next smaller diameter pipe with just a small decrease in effectiveness.

You could also extend the length of your exhaust pipe past the critical 70 inch length somehow., like have the driver’s side exhaust exit on the passenger side, and vice versa.

I just stuffed a blanket, a comforter, a pillow, a large sleeping bag and two foldable mattresses in the trunk and it didn't do much of anything. Granted, there was still a void between the battery and the quarter panel and a little over the rear end but it was 90% filled. I just didn't want to mess up the sheets or anything. I tried to film myself driving the car to capture the drone and ironically, my phone cannot pick up the drone frequency. So, everything sounds fine on the video when it is obviously annoying in real life.

I can call the exhaust guy to see if he's heard of or would be interested in a Helmoltz-style resonator, but it didn't seem like he had any idea of what it was or he probably would have brought it up.

Is that 70" past the muffler? Rear End? Does it have to be a straight line of tubing?

Tailpipes from the muffler exit out to the open end that measure 55 to 70 inches length on V8s tend to have an annoying drone somewhere at an RPM and throttle opening typical of highway cruise.

The stub pipe does not have to straight.
Think of all the curves in headers.
The science phenomenon that causes drone is the same one that gives added engine power with headers.

Alright, I'll measure under my car. But on the other hand, I've been trying to see how some OEM's do it. I found the underside of an LX Charger and it has a muffler in the center followed by two resonators by the tips; however, like mentioned, there is plenty of exhaust length (> 55"-70") between the muffler and tailpipes.

I also found some dual outlet Borla intercooled tips on Amazon prime that I really liked and are marked down like 65% compared to Borla's website. Or I can get standard round ones for $20 cheaper per tip. I might pull the trigger on those more for looks over trying to help the drone.

The Dart has a longer wheelbase than any Cuda. Yours is 111" and the 67-69 Barracuda/Cuda is 108". The E body Barracuda/Cuda is also 108".

Fix... "Different wheelbase*"

Yeah...
It is odd that subtle changes can make huge differences, right?
You could duplicate a winning formula from another car with only one small change and it can end up sounding different.

So Sunroofcuda's offer to build you a set of resonators that are 3.5" body was not sufficient? He gave sound advice, and your YELP dude muffler shop is an idiot because the factory did install resonators to get rid of the drone!

You keep asking questions for answers you are seeming to ignore. Just cut the friggin tail pipes off, move the mufflers forward, install the resonators and extend the tail pipes past the bumper.

That LX Charger underside picture shows many “tricks” to get rid of drone while keeping back-pressure low. There are also aerodynamic tricks that older cars did not have.

It would be even better if we could see inside
the big center muffler AND
inside the smaller two “resonator” type units near the rear bumper.

There might be T-stub pipes hidden inside.

I also would not be surprised if the distance between the two exhaust ends is critical too.
It might partially cancel a particular drone noise at a particular RPM.

Is there any Sales Literature that states that the LX Charger factory Radio/CD/ MP3 player has Bose-like noise cancellation electronic circuits?

Alright, so I went to an exhaust shop Friday and had them install some Helmholtz resonators. I had to do the math for them, but I came out to needing about a 25" long resonator. The muffler shop I went to was great. Really cool mom and pop place. Overall, the car is a little quieter, sounds a little different, and part of the drone has gone away, but not completely. Aside from exhaust tips, I think I am going to stop messing with the exhaust. Let's face it, I'm throwing 500+ hp through a tiny tube. I'll just cruise at 60 mph instead of 70 mph. I'll save gas anyway. Anyway, thanks for your help!

I used a cellphone app ("sound analyzer")to measure the resonance frequency. You might find that a small change in the length of your resonator might finish off the rest of your problem.

Glad you had some sucess and part of the drone is reduced.

Exhaust tips that are small mufflers will help a bit more.

I do not understand how you decided on the 25 inch length for the stub without measuring the frequency in Hertz of the drone sound beforehand.

Changing your fuel chemistry will probably change the frequency of the drone a bit
and/or the rpm where it is maximum loudness.
You could try “pure gas” without ethanol,
or create a test blend by adding some E85 to regular E10 gasohol.

Hotter summer air temperatures will also change the drone a bit.

I did measure it on my drive over (133 Hz). The equation I used that involved Hertz gave me a J-tube that was like 22 ft long. I either did something wrong with my units or had the wrong equation. It's very difficult to calculate the speed of sound as well as it's a function of multiple variable. I assumed standard pressure but a temperature of about 450-500F. After I had done the math using the 1/4 wave equation, I checked on other forums and they seemed to have some sort of success (whether minor or dramatic) when dealing with drone at 2000 rpm. So, I figured I was in the ballpark.

The plan in the future is to change the exhaust tips. I'm not sure to what, yet as I want something a little unique. After I graduate from my Master's in June, the plan is to remove the entire fuel system and install a Tanks Inc tank with a Fitech throttle body. So, that may change everything.