Converting Your Imperial's Exhaust System From Single To Dual Exhaust


Imperial Homepage -> Repair ->Exhaust System -> Converting

Tips and performance overview from Ross:

I know many people feel that since the Imperial is "a luxury car and being treated as such" in regards the value of converting to dual exhaust. First off, changing the exhaust system to something outside what the manufacturer specifies is pretty much a violation of federal law per emissions regulations. If the factory offered a dual exhaust system for that model in that model year, one "may" convert it if all pieces are per, again, specification. Otherwise, one runs afoul of the sniffer police. Irrelevant (and dumb, admittedly), even if one adds a second catalytic converter (on
cars so equipped) so that emissions may actually be lower than the car in it's stock form; it still isn't legal.

Here's a recipe for a much better stock exhaust system which is good enough to obviate the need for a dual system and garners no evil eye from the
inspector: Replace the stock manifolds with higher flowing cast iron factory pieces (or aftermarket headers with a California Air Resources Board Executive Order number -- generally written as CARB E.O., then a number; more on headers below). Have them magnafluxed or inspect them very carefully for cracking at flanges, "bends" and at A.I.R. tubing flanges; check the mounting points as well for cracks. Use a straight-edge to check the engine-mount side for straightness; sometimes possible to have a machine shop to do some light grinding, though few will guarantee against cracking while so attempting. If good, sandblast them and prime and paint with a very-high temperature paint specified for exhaust manifolds/headers (Eastwood Company; Bill Hirsch; POR-15, etc.) or better yet have them sent out to the folks at JET HOT or HPPC for a true thermal barrier coating which is pretty much a lifetime protection. Have them do the interior as well; bye-bye rust, and easy clean-up forever.

Get a hold of some copper exhaust gaskets (SUMMIT or JEGS), ARP or similar high quality studs to attach to the motor and at the flange (also copper-gasketed; eliminates blowouts forever); enlarge all fastener holes by chamfering edges with a DREMEL tool or similar that you may be able, while installing, to move the fastener around a bit. EASTWOOD sells a tool which supposedly aids in installation by helping line up the fastener holes, but I have not tried it.

As for headers, the best have Blanchard-ground flanges of at least 3/8" thickness preferably 1/2", with primary tubes of at least 34-36" constructed of 14 gauge mandrel-bent tubing. Anything less than this and one runs into heat-related problems. Suffice it to say that many headers are less well constructed and hold up pretty well if metallic-ceramic coated (a "true" thermal barrier coating is not as pretty or shiny as the header coatings most folks mistakenly assume is what they've gotten; be sure to ask) and if the owner doesn't mind a bit more exhaust-related sounds emanating from under the hood. A set of well-constructed headers for a luxury car has these benefits: the motor gains 15-25 horsepower above 2500 rpm, the torque curve starts a touch later but is generally broader and the motor is significantly more responsive than before. The type of header described a above and installed with a true thermal barrier coating is not subjectively more "noisy" than cast iron manifolds; but don't ask me where to get a set for your car!  Unless one has a more popular model car or pick-me-up, it is a custom job to get such headers. HOOKER makes a set which will fit B/RB block C-bodies 1968-1973 (Part #5113 in their "Super Competition" series; lighter metal gauge than above). High flow cast iron manifolds are the best overall bet, but significant breathing ability is lost above 2500 rpm and a serious performance difference after 3500.

Headers should also be installed with copper exhaust gaskets at the head and at the down-pipe; fasteners should also be of the highest quality and a company called STAGE 8 makes locking fasteners to obviate the age-old "leaking header" problem.

Exhaust tubing should be specified as: 14-gauge, aluminized mandrel-bent.

And sized to complement the motor and type of driving expected (a tow vehicle needs slightly larger diameter to reflect it's more difficult job). Down-pipes should be 2.25" to a Y-junction (FLOWMASTER makes a beauty, get it!  Don't let the local exhaust shop cobble something together as integration of this piece is central to best possible flow. This is also a good spot to mount the O2 sensor if needed. It may mean that the converter may have to be moved rearward slightly, but this is a minor problem to solve in most cases.)  The converter should be an aftermarket high flow piece with the largest "frontal area" of monolithic construction (WALKER and others).

Rearwards from here the tubing should be 2.50" minimum, preferably 3.00" in a single pipe system behind a V-8; again, be sure to specify mandrel-bent tubing. "Mandrel-bent" means simply that a steel ball or other piece is inserted inside the tubing as it is bent to ensure that the inside diameter remains constant. The usual press-bends made by the factory and local exhaust shops REDUCES the interior diameter for a significant loss of performance overall. The motor "sees" only the narrowest point in the exhaust system AS A WHOLE, obviating the care one has taken to otherwise ensure a good exhaust system.

As to mufflers one has an enormous set of choices, but be aware that many good "performance" mufflers exist which are not subjectively noisy. Were I looking for a "quiet, but free-flowing" exhaust system I'd contact the folks at BORLA who are known for their ingenuity and the very high quality of their products and talk with them about a muffler/resonator combination. The usual "Sears" muffler I see folks put on their luxury cars does nothing more than cause the motor to have to work harder than necessary. The goals of quiet and performance are in no way exclusionary of each other, in fact, the usual lousy muffler causes the motor to run hotter (needing fuel delivery and ignition changes deleterious to fuel mileage/performance/engine longevity), sound like Mrs. Beasley's Kirby vacuum cleaner and needing replacement due to accelerated corrosion in only a few years. Caveat emptor.

I've also heard folks complain about their noisy "performance" exhaust systems for a reason so simple it is not often considered: the quality of the hangers needed to muffle extraneous chassis resonance: Again, don't let the local exhaust shop put school bus-style hangers on the vehicle, but take the time to research what well-insulated hangers are available. Chrysler made very good ones for the years I'm most familiar with, and they cut down interior resonance significantly. There is a lot of unexplored territory here, so look around.

Also, one may have the entire system metallic-ceramic coated for rust-proofing and some sound-reduction qualities as the system will not act so much like a radiator of heat, but will now retain more, keeping pressure and flow values high out to the tailpipe. Heat = pressure, and the attenuation (read: modification) of one will have an effect on the other.  Take into consideration also that the sound from the interior is different from what one hears ten feet from the vehicle. While I admire what hot rodding friends have done with their exhaust system problem-solving, it does not necessarily mean that any part of their solution is somehow wrong for me; in fact, as noted above, MUCH of it can be suitably modified to my needs of better performance/fuel mileage/longevity and non-objectionable sound levels and noise qualities. The high-performance 440's of the late 60's-early 70's used the same mufflers in C-body applications (including New Yorkers) as did the B-body HEMI-engined cars, often called the "Street Hemi muffler" and still available from several sources. I never knew anyone to complain of their "sound" way back when.

Finally, a bone to pick: My reading recently of "quiet" exhaust systems (and of other solutions to non-problems from my viewpoint) is as follows: My grandfather (b. 1896) had Chrysler products during my lifetime, among them a '61 300 convertible. I recall he and my old man talking once about "old man's cars" by which they emphatically did NOT mean the lumbering whales of common parlance. Instead, the meaning was that to drive well as one aged and as reflexes and energy declined (and income had probably peaked) one could afford to drive a heavy, big inch automobile with all the creature comforts IN ORDER TO BE ABLE TO KEEP UP WITH THE YOUNGER DRIVERS. Even better them, in many cases. Any old fool can mash the gas to give the appearance of being a driver, but at the end of a long day, a thirtyish fella in a Satellite coupe with 383, AT, AC, PS, PB won't get to "there" any faster than Granddaddy in that 1200 lb heavier 440-powered Imperial. And age won't keep Granddaddy from feeling worn out from having to work to keep up. Transpose our man at age 37 in that '69 Satellite and then again at age 72 in the Imperial in identical circumstances and I think you'll see what I mean. An Imperial of the right vintage is one hellaciously good-handling, braking, accelerating and riding car . . . what a pity to dull its' edge to suit what a Linkun/Cadillac driver who only tootles around town would want. No blue hairs allowed, ya'll, that Imperial is a road car, and one of the best. Keep up the performing end of the car solution to time-and-distance problems. Chryslers WERE better, for reasons which INCLUDE performance.

Tip from Brad (1964-66):

This should be the final thread from me on exhaust issues. For those of you who decide to put dual exhaust on your '64-'66, here's the Walker Muffler part numbers for the resonators (actually small glasspacks). If you're going to have a muffler shop order them and do the work, the part number and price is: 17182 - $42.95 ea. 

If you go to an Auto Parts store and do the work yourself, the part number and price, same part, different #, is: 21852 - $62.89 ea.

Question from Zeke:

It as been said that dual exhaust does not get as hot as single exhaust does, so it is more prone to rust. Here are my questions...when you put dual exhaust on a car, do you change the temperature of the exhaust gases, or the speed at which they pass through the system? I can understand that a hair dryer works better on a higher setting, but the air coming out of a heat duct in your house doesn't get half as hot if you add a duct. Next, water boils at 212 degrees. It seems as if duals can reach this temperature, they do not need to get any higher to get rid of water...You can turn up the heat on the stove all you want, but the water will still boil at 212. Just some questions I developed not sleeping last night.


From Bob:

Quantity of gas is 1/2 - just four cylinders!

From John:

I would say that duals slow down the speed of the gases because instead of exiting through 1 pipe there now 2 so less resistance. While adding a second "duct" may not make the heat half as hot, it will certainly decrease the volume at all ducts the more that are added. I was told this when I had a hot air furnace put in my garage. With twice as much metal to heat up, at the tailpipe end of the system is not going to get that hot & this is the area as well as the mufflers that will rust out sooner. Anyone that has kept a car for a long time will probably realize that they often only change from the muffler back 2-3 times before changing the front pipes. Why?, because the front pipes get far hotter. try heating a piece of metal & after removing the heat see how relatively fast it cools down. If this is bare metal even if not gotten wet, what happens? It starts to rust because of the moisture in the air. Picture all this going on inside the exhaust system with all the bends & low spots in the mufflers etc., and you get an idea of with more surface area the more moisture you tend to collect.

Question from Dick:

Is there a difference in how loud the single versus dual exhaust systems are?

Reply from Norm:

I have owned and driven these cars with their original installations of single and dual exhaust. Properly done ( using components as originally specified ) there is no difference in the noise level between single or dual exhaust either inside or outside of the car. Note that these comments apply to a 64-65-66 both sedan and convert. Re: 68 - we had one new and it had a muffler and resonator ( single) . It was very quiet. As you have probably noticed, the FSM does not show a resonator in the dual system.

From Jack:

Well, I wanted straight pipes like the ones on my 65 Galaxie 500XL, but Annette said there was no way in h--- that was going to happen. Guess I ain't old enough yet to let the sound of an unmuffled big-inch V-8 annoy me. In retrospect Annette is right, a car as classy as the Imperial just wouldn't be dignified sounding like a pro-stocker. Kind of like Margaret Thatcher in a leather mini-skirt, it just wouldn't be right.

Question from John (1952):

I need to repair the exhaust system on my '52 four door sedan. I had the engine idling for an extended period, and the plugs loaded up. I tried the old Italian tune-up trick to clean it out. Worked a treat, except for one nice backfire that blew a hole in my very original, very rust-challenged head pipe.

Too bad; before this the car was so quiet you would not know the engine was running unless you had the hood open and saw the pulleys spinning. However, what a nice sound from that Hemi with the hole in the head pipe!! It has that perfect big V8 rumble.

So, now I am thinking about departing from stock, but just a bit. I'm thinking of installing dual exhausts. Has anyone done this -- are prefabricated dual exhaust pipe kits, including head pipes, available? Or should I just have a set custom made?


From Kerry:

I'm not sure about the '52 but my '54 had dual exhausts from the factory. Any muffler shop can build you a new headpipe.

Standard mufflers are considerably louder than stock and thrush wll be even louder. When I first had the mufflers put on the '54 to replace the rotten original system, the Minike shop used their standard muffler. They looked OK but were loud and did not sound right. A week later I came across these NOS mufflers and had them installed. HUGE difference! You could barely hear it run at idle but enough rumble when you got on it to know it was big American iron under the hood.

From Arran:

The 54's had the same body as your car but had a dual exhaust from the factory. All that your muffler shop has to do is look up the routing scheme for a '54 Imperial or New Yorker Deluxe and you are all set. By the way they used straight through mufflers anyhow so Thrushmasters will do a nice job. Its a cheap way of gaining a few horses since your gonna replace the system anyhow.

From David:

Try Andy Bernbaum in Newton, Ma. 617-244-1118 orWaldron's Exhaust 800-503-9428.

Question from AJ (1965):

I need some help selecting a good exhaust system. I own a ' 65 Imperial Le baron 4 door hardtop. 413 motor, not hp. Should I keep it single or is dual exhaust better for it and what muffler would you all recommend? I was going to go with the Dynomax turbo. I think that's the right name. If anyone could give advice to me on this I would greatly appreciate it.


From Stevan:

You should go with dual flowmasters as I have done on my ' 72 Imperial.  I also went with 2 1/2 pipe.

From Matt:

I just had a complete exhaust replacement from MIDAS here in Wichita and was lucky to pick the one with a car nut manager. I put on turbo's and all pipes from the headers back. The resonators were not installed. Although not stock, I had him put on two beautiful chrome downdraft exhaust tips-really looks smooth! They are very quiet (so far-may be a little louder when burned in). He gave me those free!!! Imagine that. Also, the price started at $635 but ended up at $535. The job was well done, bent to factory specs for the most part, and made sure the emergency brake cable was clear and free. I have Flowmasters on my '73 Javelin AMX (401 CI), but they are not the sound I'd put on my Imperial. Although they are a low deep rumble.

From Mark:

Flowmasters are nice, but them's LOUD muthas! Easily twice as loud as the Dynamax's. (I finally had to change out my 3-chambered Flowmasters for the Dynamax Turbos on my '66 Plymouth convertible.

From John:

One big problem with duals is they don't last as long because they don't get as hot & allow a lot of moisture to sit in the system & rot them out Unless it is a regular use car.

Follow-up from Norm:

This may be so, but my ' 64 convert had the same duals on it the day I sold it ( three months ago) that I bought it with in 1989. No problems.  No leaks, no rust. 20,000 miles in ten years.

From Brad:

I had a dual exhaust installed on my '66 and I am very satisfied with the results. It is not a factory setup, as LeBarons came only with single exhaust, but I like it. One thing you need to have the muffler shop ensure is that they leave enough clearance to service the center bearing and support on the drive-shaft. The bearing is very close to where the exhaust pipes have to snake under the frame. The place I had it done turned the pipes outboard immediately after they were routed under/through the frame. This left room to easily get a wrench on the bearing support if I needed to. They also installed a crossover tube just forward of the bearing that will double as a convenient place to rest the front part of the DS when I do have to service the bearing and U-joints. A second hanger needs to be installed for the second muffler, but there's a flat spot to install it opposite the original. It looks "very factory" but we know better :). I had them route the tail pipes and secondary/silencer mufflers on either side of the gas tank like the coupes. Other list members had some valid concerns about the pipes not getting hot enough to burn out condensation, which of course leads to rust-out and a short lifespan. I agree this is quite probable, but, If you were given a price quote anything like me, you can't afford not to "dual-it-out". I paid a local (not chain!) muffler shop $375. That's all four "lifetime" (whatever that means) aluminized mufflers, aluminized pipes and the crossover weld job. The job was $20 more than a single exhaust. Heck, I paid that much 20 years ago for dualing out my '69 Charger. I found it quite reasonable. Shop around for such a deal. 

Question from Mike (1967):

My exhaust system is blown and I need to replace it.  I figure I might as well get duals put on...hey, maybe even have the guy put on an 'H' or 'X' pipe while I'm at it...

Reply from Rodger:

Since the exhaust is shot go to the duals.

Find a couple of factory performance mufflers (2 1/4 in-let / 2 1/4 out-let and a 21 inch long oval shaped housing) and the matching resonators ( from a 375/390 440 or 426 powered big body MoPar).

Your local performance muffler shop can do the bends for you (w/the cross over pipe).

I've done this twice in the last two years and found that I still have the Imperial quite-ness with better power and mpg figures.

Follow-up question from Marc:

Is there any benefits to the cross over pipe between both exhaust pipes?

Reply from Rodger:

The cross over pipe must be the same diameter as the exhaust pipes. The benefit is at low rpm's. After that its as if they're not there.

Question from Tim (1967):

I'm looking for opinions (or better yet, photos!) of what you folks think the tailpipes of a dual-exhaust-converted '67 should look like.

Here's why I'm asking...

When I bought it, my Imp had the stock, single exhaust. But some amateur mechanic had messed with it at some point and left a number of leaks, conveniently located so as to direct exhaust into the windows when rolled down. Eventually I took it to a local (non-chain) muffler shop, and allowed myself to be talked into having it converted to dual exhaust rather than simply having the leaks closed up.

The good results:

A number of postings in the IML archives suggested that Dynomax Super Turbo mufflers were appropriate ones for an Imperial, so that's what I went with, and I'm happy with that choice. And I'm glad I had the conversion done, since the car is noticeably more responsive now -- it used to roar and *then* go, but now it roars and goes at the same time. :-)

The bad results:

I was a babe in the woods when it came to specifying what the tailpipes should look like. Chrome tips? Pointing down or to the side? Heck, I didn't know. So, regrettably, I told the installer I'd let him use his judgment -- with the understanding that an Imperial is a luxury car, not a muscle car.

Silly me. He decided it was a muscle car after all. So now I have two pipes sticking way out beyond the bumper, with downward-pointing chrome tips. I thought I'd get used to it, but I haven't. It'd be fine for a hot rod, but it just looks wrong on an Imperial.

Hence my question: What do you think it *should* look like? I'm not too concerned with making it look stock, although I'd certainly consider doing that if I knew what a stock dual installation looked like.

To make matters worse, there still seems to be a significant leak. At least, *something* is causing a cloud of smelly exhaust to collect around the front of the car at stop signs and in the garage. So I think I'll be going to a different shop to have them expunge the sins of the first shop. Anybody know of a good one in North Dallas?


From David:

Do you have an oil leak that might be dripping on an exhaust pipe or manifold causing the cloud in the front?

I would think that the pipes would look best if you could barely see them. Perhaps brought to the rear corners and turned down with the tips barely showing past the bumper.

From Jay:

I have noticed that many non-muscle cars of the late '50s and early '60s have a tailpipe point straight out the back of the car, with a standard straight cut on the end. (no angled "hyperdermic-needle" look) Most of the pipes that I noticed had a chrome tip that has a rounded/beveled edge. I like this look and it also has the advantage of being safer as you cannot cut yourself on this type of tip. Basically, that is a description of the exhaust pipe on our '62. The tailpipe ends about 1" behind (to the rear of the car) where the chrome bumper starts underneath the Imperial. It does not stick out past the bumper by any means. I think that two of these would look nice on a '67, and someday I will have two of them on my '62.

Downward turned exhaust pipes and ones that stick out past the rear bumper will eventually get dragged across a steep driveway. Just ask anybody that has owned a lowered car. (been there, done that!)

From Dick:

On a '67, the pipe ends about 1 foot in from the rear bumper, with a turned down section of pipe which is just long enough so that the horizontal cut line of the end of the pipe just misses the straight part of the pipe. Very elegant, and absolutely impossible to see, unless you assume a very un-Imperial stance behind the car and peer up under the rear end, which I am sure no gentleman would ever do. It appears that no concern was evident regarding the exhaust fumes finding their way into the car, even though the exhaust is dumped almost under the middle of the trunk floor. Perhaps the sealing of the trunk floor is so good that this was not an issue.

From Rodger:

The smell that you notice when you come to a stop ( like after a run down I - 75 ) could be from a valve cover gasket leaking down on the exhaust manifold.

The best looking exhaust tip is one that looks kind of like a question mark. As the pipe comes out of the resonator it should curve up and then down-ward. At the point when the radius of the bend is even with the lowest part of the straight section of the pipe...cut it even with the straight section. This will leave you with a pipe that is pointing towards the ground and it will be hidden from view.

Question from Dale (1968):

One of the projects I am in the middle of is having new dual exhaust installed on my '68 Crown Coupe. The shop is not doing a very good job on my car. Who ever heard of glass packs on an Imperial?? In conversation with the owner of the shop, he tells me that his spec books do not show mufflers and resonators on the dual exhaust systems for '67 and '68 Imperials. Does anyone know if this is correct? I am having a lot of resonance in the car and it seems logical that the car should have mufflers and resonators. I told the guy that I want the car to be quiet... and so far it is not! He has installed 2 1/2" pipes which is not stock factory spec. Why he did this I do not know and I did not ask to have them. I keep going around and around with the guy and all I want is a system that is quiet and reasonably correct as to factory spec for a '68 Crown coupe. So, I need some of your knowledge and expertise. Anyone who can give me some correct information that I can use as ammunition to point this guy in the right direction would greatly be appreciated.  


From Dick:

This is not going to make you happy at all, but I have had exactly the same frustrating session with my 68 Crown 4 DR. I like the car to be QUIET!, so I asked the man to install new mufflers and resonators per factory original, the result was too noisy by far. I complained, he put in a crossover pipe, some help, but still not Imperial sounding. I drive my 67 and smile all the while, it is quiet as a whisper, and as it is a convertible, any noise would be very obvious. But the 68 - sounds like a hot rod and I can't figure out why!. I should note that the convertible has single exhaust, maybe that's the answer.

Follow-up from Jeff:

Shops are also fond of using single-walled exhaust pipe, where double-walled was used by the manufacturers, even in the lesser makes of Chevy and Ford. This will make a BIG difference.

From Leo:

The fellow is right. I looked at my '67 manual, it showed a resonator at the back beside the tank on a single exhaust system. On the dual exhaust system, it showed no crossover or resonators, just two mufflers.

From Jeff:

Shops are also fond of using single-walled exhaust pipe, where double-walled was used by the manufacturers, even in the lesser makes of Chevy and Ford. This will make a BIG difference.

From PEN:

As far as I know, the last year all Imperials came with dual exhaust, mufflers and resonators (that's the way it is spelled in my service manual), was 1961. In '62, Imperials went to single exhaust, with one muffler and one resonator. The reason was that factory dual exhausts rusted out and developed leaks in cars that were mostly used for city driving. In city driving, the dual exhausts never got hot enough to evaporate the H2O out of the pipes, so they rusted. Now that stainless steel custom exhausts are available, when I can afford it, I'll order a dual stainless outfit for a '61 and put it in my '62. I'll have to modify the support under the drive-shaft center hanger bearing, but that should not be too big a problem.

From John:

I don't know the "correct" information but I too went 'round and 'round getting my dual exhaust setup the way I wanted it. I got a pair of the so-called "turbo" mufflers put on my '65, and when I got it back it was too loud, and it resonated to the point of being uncomfortable. The solution was to add a pair of glasspacks just forward of the tailpipes, which calmed it down considerably. It still doesn't sound like a stock Imperial but that's not what I wanted. I don't remember but the shop may have used 2.5" pipe (aluminized) for lower back pressure. It sounds really nice! Not obnoxious and not quite "hot rod," but definitely noticeable. In '65 the convertible only (I think) came from the factory with duals and four mufflers, two acting as resonators.

From Jon:

I had dual exhaust put on my '77 New Yorker Brougham, a couple months ago. They did a GREAT job on the exhaust, and made a cross-over pipe. The only problem was......they put "Turbo" mufflers on it. My dad told me that turbo mufflers were "quiet", and are nice. Yeah Right! My car is a lot louder now (but not TOO bad). My dad LOVES it that way, but I hate it! (I have absolutely no respect for muscle cars or hotrods, my dad is the opposite) We bought some new very quiet (supposedly) mufflers for it, to be put on. I hope that will make it Imperially quiet. My car is perfectly original otherwise, and I want it to sound that way.

From Kne:

What kind of mufflers did he put on? I hope he didn't put on some turbo mufflers, which is still the rage right now. First off I'd leave the 2.50" pipe/system on, it is a GOOD thing, and again, will not create more noise in itself. Then I would go out and find some big 2.50" mufflers of the conventional type, maybe something intended for a single exhaust truck system, and have him put those on instead of whatever he put on there. Then, for a resonator, just run a pair of glass packs right behind the main mufflers so you don't have the hassle of getting resonators to fit behind the bumper, beside the gas tank, etc. Yes, glass packs behind conventional mufflers will reduce noise further. No they will not make it sound like a drag car, if used this way. Glass packs come in all lengths, so it should not be a problem finding some that are just the right length to fit behind the main mufflers. Get the longest ones that will fit. Imperials are long cars, so you should be able to get lots of muffler under there. Also, VERY important to cut down noise: (and add torque) be sure he puts a cross-over pipe/balance tube between the right and left side pipes, in front of the main mufflers. If he hasn't already done this, this could be much of your noise problem. If he has, I'd say the mufflers he has put on are too small, or are of the "turbo" design, or there is something wrong with them. But if this was a contest, I'd guess that he has not put in a balance tube/cross over pipe. If price is no object, (and most good shops should not charge for the first cross over pipe) I'd put another one in the section of pipe between your main mufflers and the secondary/resonator mufflers (the glass packs) behind the main mufflers. (whew... am I making sense?) Just an idea, but I think this would be a whisper-quiet system. 

From Elijah:

Several years ago, I decided to have dual exhaust put on my '71 Imperial. My first experience with a muffler shop was terrible -- the guy was completely unwilling to work with me *after* he had screwed up the job. The next place I took the car to did better, but it was still WAY too loud. This guy was willing to make adjustments after the work had been done, but never seemed to be able to get it right. Earlier this week, I took the car to a shop here, and before I could even tell the guy what I wanted done, he put the car up on a rack, and started pointing out all the problems -- I knew the car was in good hands. After about four hours of work, a bunch of welding, a new crossover pipe, and about $80 (which was very reasonable, IMO), I had a much quieter, more polite Imperial. The way the system is now, it's still louder than the original, single exhaust was, but it's far better than it has been for several years. Most of the loudness I had been hearing was the result of leaky joints among the pipes and mufflers. The addition of the crossover pipe helped too. The car has two stock mufflers (no way would I let someone put the Turbo mufflers on!). I wished for glass packs at the rear (which make GREAT resonators!), but the configuration of the frame rails and off-set gas tank won't allow room for them. Alas, if the owner of the shop you took your Imperial to isn't willing to work with you, you may have to hunt around until you find someone who will. Many times, it's just a matter of finding someone who's willing to put forth a little extra effort to make sure that the job is done RIGHT!

Question from Arran (fuselage era Imperials):

This is somewhat of a dumb question but since the fuselage cars can't fit a dual exhaust easily could one just use a larger diameter single pipe? I know that the dual pipes are used for cutting down on the back pressure but could you achieve similar results by using, lets say, a 4''inch single in place of a 2-1\4'' single? Just speculating, I don't even know if you could get a 4'' pipe or the muffler to fit it.


From Robin:

I have had duals installed by Midas on my '70 Newport and my '72 Imperial with no problems at all. No resonators either and I am not sure what the noise problem seems to be unless you want whisper quiet. For myself a big block Mopar, be it Imperial or otherwise, needs to breathe and express itself. Both have H pipes as this is fairly standard for increased torque and are 2 1/2 " systems. It is a bit expensive at Midas but they do a good job and have good warranty. Single exhaust just chokes that engine,duals are one of the simplest mods to increase efficiency.

From Jim:

I had a local shop (Castlerock, Co) put duals on my '69 Lebaron several years ago and have had no problems. However for some reason they didn't put on an H pipe, so I had my local Midas shop add one and it really improved the sound and the performance.

From Demetrios:

Yes, this should work just fine. Many high performance modern cars w/ V8's do exactly that. The reason they are doing it is so that they can have one oxygen sensor and/or one catalytic converter and save $. The only down side is that you lose a bit in sound "quality". Keep in mind that the exhaust restriction proportional not to the pipe diameter but the pipe cross section area. So, a 4" pipe is 4 times less restrictive than a 2" pipe.

Question from Norm (1973):

I owned a '76 Dodge Royal Monaco Brougham with single exhaust. I wanted to install duals on it and was surprised to learn that I would have to remove the 26 gallon gas tank and install a 20 gallon one in order to make room for the other pipe.  This was the case from the factory when a dual option was ordered.  Is this a consideration in the case of a '73 Imperial?

Reply from Pete:

Yes, I would have to do the same thing, but I won't. I'll see if I can route the pipes just behind the rear wheels. Provided its tucked up enough, they shouldn't be too noticeable. After all, I'm after two things: 1) A little more performance, and 2) reduce the heat radiated from the exhaust pipe on the passenger side. As I've mentioned before, the passenger floor get VERY hot and the current pipe is actually FARTHER away from the floor than it should be.

Question from Randy (1973):

I have a '73 LeBaron with the factory single exhaust and would like to change it to duals. I have noticed when looking under the car, that the single exhaust pipe runs between the fuel tank and the chassis rail on the right side. However, there is no room on the left side between the tank and the chassis. That means to put on duals, I would have to run the second pipe on the outside (ugh) or under (also ugh) the chassis rail. I seem to recall that duals were an option on one of the fuselage years but don't know which one. Is it possible for me to obtain a fuel tank from one of these factory dual exhaust fuselage Imps and install it in my '73?

Reply from Elijah:

It is indeed possible to install dual exhausts in your '73 Imperial. However, based upon my experience with one of my '71 Imperials, I would not recommend it.

First, no fuselage Imperials came from the factory with dual exhausts (unless someone with lots of pull managed to special order it, in which case you'd be incredibly lucky to locate such a car.

Other fuselage C-Body cars of this era could be ordered with factory dual exhaust. However, the factory setup for these cars did NOT include resonators at the rear. So even if you locate an original gas tank from a New Yorker with factory duals, there still will NOT be room for resonators at the rear.

The two major issues I ran into in having dual exhaust put on my '71 were pretty simple: first, I had to take the car to FOUR different custom exhaust shops before I could find someone who could get all the rattles and knocks out. Second, since resonators could not be installed at the rear, there were several RPM ranges where the noise was absolutely deafening, something I did NOT want in my Imperial.

My "final solution" was aluminized pipe, stock mufflers, and an H-pipe. The last length of tailpipe is actually run along the bottom of the frame rails on each side at the rear, which has proven to work pretty well. The H-pipe not only turned out to help with the rumble that I got at 45 mph and also at 65+ mph, but also gave a noticeable improvement in low end torque.

And when I replaced the interior a year or so ago, I insulated the living daylights out of the trunk, rear seat back, and floorboards. That cut out about 90% of the "rumble," so now the car is much more Imperial sounding on the inside. :o)

Now, to give you a better idea of this process . . . I first had the duals installed in 1995, but it wasn't until 2001 that I was at last satisfied with the system.

My "new" '70 Imperial had been changed to dual exhaust before I bought it. One of the first trips the car will make this month will be to an exhaust shop to have it put back to the correct original single exhaust.

Question from John (1973):

My car has a wonderful 440 and is all original but I would like to know if the Imperial line ever put out a car with a dual exhaust, mine is single and no where in the original literature do I find the option of having a dual...was it available in 1973? was it ever available? (or is this just a Canadian thing) Has anybody attempted to put a dual exhaust on their Imperials here on the IML? What are your opinions and advice...I think it would be wonderful to have (and I hope nobody is thinking I'm ginking up the car I just like the look of 2 pipes at the back and the gentle sound it produces as well as improving the performance slightly...not that it really needs it)


From Joe:

The FSM for '73 shows that the Imperial, Chrysler and Plymouth Fury had a single exhaust system when equipped with 400 2bbl, 400 4bbl and 440 4bbl engines. The Plymouth Fury was available with dual exhaust as an option. It should not be difficult to get a similar system fabricated by a good muffler shop. While not original, it helps the engine breathe better and get slightly more power.

From Matthew:

I have duals on my '74... sounds great! I had mine bent at the local Midas cost about $400.  Go for it!

From Kerry:

You could always go to the dual pipe single muffler and split the pipes out. This type of muffler has two inlets and two outlets. It should fit where your current muffler goes. Normally they can take both pipes over the rear axle and split there. If there is not room in the front, go to a 3 inch pipe

From Pete:

I'll let you know in April! That's when my 4dr get duals. You may have to shift the fuel tank to make room. That's not something I want to do.  I plan to route the driver's side pipe BACK OVER to the passenger-side just behind the rear diff. I'm not concerned with evenly spaced pipes out the back, since they will be almost totally hidden anyways

From Kne:

Dual exhaust is something every Imperial DESERVES!!! It is something that the factory "would have done" if they thought they could have afforded it or that it was cost effective.  Dual exhaust does not gink up a car. It brings it closer to it's real potential, closer to what the car would have been had the factory been able to spare no expense. It does look better. It does sound better. The factory did not use single exhaust because it was "better", but because compromises have to be made somewhere to stay within certain established cost parameters.  

Question from Roger (1974):

I am putting dual exhaust on ' 74 Imp. What is the reason for recommending cross over pipe and which muffler is the quietest. 


From Brad:

The crossover tube equalizes back pressure in the upper exhaust system. This equalizes the gas pressure on all of the cylinders, resulting in a more even combustion and power stroke. In other words, the back pressure forces the exhaust stroke gasses to exit the cylinders at the same rate, equalizing the effective "space" available in the cylinder for the intake charge and pressure stroke. This is not an issue on single exhaust cars due to their exhaust pipes coming together where they do. If a crossover tube is not installed on dual-exhaust cars, differences in cylinder pressures will result in uneven combustion and loss of power (negating the higher volume properties of the dual pipes). I have never noticed either muffler being more quiet than the other, just an even "lub-lub-lub". Now you get to get into the discussion about the merits and expense of this conversion (more HP versus quicker rust-out).

From Steve:

If you are going to put dual exhaust on your '74 Imperial, a cross-over or "H" pipe should be installed as close to the exhaust manifolds as space permits to get the most benefit from the 2 exhaust system. I won't go into the reason for it because someone else did in another reply to your email....and described it well. As far as mufflers go, usually the quieter the muffler...the more restrictive it is. I once purchased a pair of "Sonic Turbo" mufflers with a 2 1/2 outlet and inlet. They were a great compromise between noise and restriction. I am not sure if they are still made today. Generally an open, unrestrictive exhaust system is great for top-end high RPM performance but is not very helpful when it comes to low RPM power. And a factory low performance exhaust system is good for normal driving and is better for gas mileage. Did you ever notice how sluggish a car becomes when it loses it's exhaust system??...but if you take it out on the Hi-way it seems to have more high RPM power? Same principle.

Question from Roger (1974 - 1975):

Has any one in the club put dual exhaust on a ' 74 or ' 75 IMP. If so I would like details.  Will I still need resonators?


From Rodger:

If you will purchase two good quality single exhaust mufflers (just like the one that you already have), and then go to your local muffler shop (do ask around for who does the job for the best $$$) and tell them that you would like a dual exhaust using the mufflers provided with a cross over pipe...they will fix you up.

You do want new parts from the exhaust manifold to the rear bumper. 

Also if you will look at the "hot" 360 Dodge's for the same year it will give you a sense of direction (and you can order the complete system and do it yourself).

When all is said and done you will get better mpg's and a better throttle response.

From Elijah:

Yes, you will still need resonators -- without the resonators at the rear, you'll have a very un-Imperialistic rumble from the rear, especially at highway speed.

Question from Jamie (1977):

Is it going to be possible to put true duals on my '77 NYB? I'd sure like to have some to wake the car up and a 9:1 440 may be in the works soon as well. The '78 parts car sucked on power when I test drove it, and thats likely due to the low compression and single exhaust. Could have been the ELB, but that was replaced by a points distributor!


From Brad:

Duals on a NYB are perfectly possible. The underside of the car is made to accept them with the exception of the gas tank. The stock single exhaust runs between the frame and the fuel tank on the right side but there is not enough room to run a left side pipe between the tank and the frame. The tank is off-set slightly. They would just run the left pipe below the frame rail.

From Arran:

In addition to the dual exhaust it would also be a good idea to junk the EGR and the smog pump, if someone hasn't done so already. Part of the reason that these cars have such a restrictive exhaust in the first place is to accommodate the EGR system. On top of that they fitted the engine with restrictive exhaust manifolds for much the same purpose, use headers or earlier style manifolds. From what I recall, I could be wrong, Chrysler played things a little differently when it came to reducing the compression ratio of their engines. Unlike the other two of the big three, Chrysler didn't use open chamber cylinder heads to reduce compression; instead Chrysler lowered the deck height of the pistons. To raise the compression of these engines, under these circumstances, you have one of three options, shave the heads, use thinner gaskets, or swap the stock pistons with ones of a higher deck height.

With regards to your '78 NYB being a little anemic on power perhaps the points are out of adjustment or you need to advance the ignition timing. You would be forgiven for installing a MoPar electronic ignition on this car in place of the lean burn, it was used fairly successfully on the earlier pre-lean burn cars. In short I think that these cars could have a lot of potentential when it comes to improving performance, especially by scrapping the smog crap. This is why I have been doing a little bit of research and bench racing in my head when it comes to the '75 Imperial sitting in a nearby driveway.

From Rick:

The way Iunderstand the DC manual, Chrysler had open chamber heads from '68 on up, with the electronic ignition and a good exhaust and an unrestrictive air cleaner that Chrysler should move vey well. I would also agree, get rid of the air pump and EGR and all lean-burn parts. If that has a TQ carb, it should work very well.

From Carl:

I had the same problem on my car, the 'fix' wasn't to try to offset the tank (not raelly feasible) but rather to pull both pipes under the framerails for a uniform look.

This is the right side of the exhaust:

Question from John (440):

I've been wondering if it wouldn't be better to run the packs first, where their smaller streamlined size might get them closer to the motor, and leave more room for bigger main mufflers behind them. Also, I believe since the packs reduce high frequency noise best, it might make more sense to let them do that, then let the main/conventional muffs muff down the overall noise level. ??  


From Kne:

The factory put resonators in front of the mufflers, which again makes sense to me. Having done many exhaust jobs under the shade tree, discussing and thinking about this, I realize that packs do cut out the high frequency sounds.

But further more, (I say!) although conventional muffs do away with all the low frequency noise, or sound in general, I have noticed that some times you will still hear high frequency sound, so I think we are onto something here for the ultimate Imperial exhaust system, using the packs as super resonators to cut the high frequency, and the muffs to cut the low frequency and remaining sound.

Well perhaps John will perform the Imperial Exhaust Experiment for us. (IEE)

Here is how I would lay it out: First I would use the biggest longest mufflers I could find that would fit under the car.

Glasspacks would be of the "louvered" type, not the ones with just a perforated tube inside.

NO TURBO MUFFLERS!!! I'd find some big honking muffler designed for a single exhaust system, maybe some truck mufflers or the old "hemi" muffler if it still exists.

I'd start out with 2.50" head pipes into 2.50" glass packs, with a cross over pipe in front of the glass packs, from head pipe to head

Then I'd reduce the pipe coming out of the packs to 2.25" and into a pair of giant humungous big old hairy-honking 2.25" conventional

Then....over the axle, and I'd still add the little weenie conventional resonators at the back, if possible. From earlier discussions, I believe you can center the gas tank if the offset is a problem.

Now I suppose you could reduce the pipe again, where it becomes tail pipe, to 2.00", as is usually done in most conventional systems,
and still have 4.00" of exhaust overall. Personally I'd stay with 2.25" tail pipes, but I can see how 2.00" tails would make sense also,
and probably still work good, better than any single system for sure. (not including a big performance single system)

Something else I'd like to do, but I believe it's location might interfere with the drive shaft, or it's removal/installation, would be to install a second crossover pipe after the packs and before the main/conventional mufflers. My theory is that it would cut down the noise about half as much again as the first crossover, and it would be good to balance the pressure side to side again as the gas came out of the packs, in case there was any difference in flow between the packs.

Even though I like exhaust noise, and prefer to listen to an engine rather than a radio, I think, in theory, this would make for the ultimate
"whisper quiet" Imperialistic exhaust system, but still flow perfectly well making for a happy powerful engine, and giving good gas

This discussion has kind of brought up the question of dual vs. single exhaust, which is more quiet.

I can't see how one muffler can really be more quiet than two, or four, but I will say there is no doubt that if you just plain choke the
engine down enough it will be real quiet, but at the cost of excessive back pressure. I mean, one could stuff rags up their tail pipe and have the world's most quiet car, but it sure would run crappy and get very poor gas mileage. THIS, would NOT be IMPERIALISTIC!!!!

Running a single exhaust, 2.00" pipe, etc, to me is like taking the rag-stuffing approach!

So, I think duals is where you can get the best of both worlds, if done right.

From Wayne:

The question that was raised was whether it would make sense to put glass packs on first and regular mufflers after the glass packs. Basically this is the set-up that I have on my 1966 convertible. All 66 convertibles came with dual exhaust from the factory. When I bought the car it had glass packs on it. When I had the exhaust system replaced, I wanted a quieter sound. Because of the X-frame, the muffler shop had trouble finding a muffler that would fit in the area allowed. Some steel packs were used. To quiet it down, I had resonators put on behind the steel packs. It is quieter now - although I wouldn't consider it "whisper" quiet. A friend put a stainless steel dual exhaust on his 66 LeBaron with both mufflers and resonators (he didn't have the X-frame to contend with). My exhaust system made about the same amount of noise as his. I don't know if he used a crossover pipe or not. Apparently a crossover pipe would quiet things down some more. I am not sure if I have clearance for a crossover pipe with my convertible frame.

Tip and question from Jack:

Picked up the Imperial from the muffler shop earlier.  Here's the lowdown:  no matter how the pipes were bent, 2 1/2 in pipe just would not clear the starter, tranny, torsion bar and all the rest of the stuff on the drivers side without looking like a pretzel so I figured straighter and smaller was better than bigger and crooked, so we went with 2 in pipe.  The mufflers are  vortec low restriction units.  Didn't really have anything to benchmark them on but the difference in performance is VERY noticeable from the stock single.  Where the engine used to 'lay down' at the upper limit of the rpm band, now it pulls like hell right to the shift point.  The tone from the exhaust is just enough to let you know that it ain't no small block under the bonnet.  Other modifications so far include a K&N air filter, an Accel supercoil and a MOPAR Performance ECU for the electronic ignition.  Future mods, a Comp cams part# 21-220-4 .432 lift 206 deg duration cam and an Edelbrock dual plane intake. 


From Mike:

Be sure to rejet the carburetor now that you have duals (I know you don't want to burn valves).

From Patrick:

It is probably best that you went with 2'' pipe, as it will last longer (because it runs hotter) and you still keep most of your torque. I knew someone who had a 85 f**d Mustang (otherwise stock), insisted on having 4 inch duals on it (no I didn't know that was possible either). I could beat him with a geo from a stoplight now.

From Ross:

Ya'll may notice that in many cases Mopar specifies a different carburetor number for not only different transmissions on an otherwise similar model, but ones sold for hi-altitude areas, different emissions calibrations, and, yes with dual exhaust on occasion. When switching over to a less restrictive exhaust it is not unusual to have to REDUCE the jet/meter size: The carburetor has to pass more fuel, but ironically (as the amount of vacuum signal increases) it takes less jet/meter size to do it. Others have noted that this is not always true, that an increase in size is warranted, and I can only say that it takes a little checking first. Just remember that changing the ignition settings (initial timing advance AND TOTAL ADVANCE) will be necessary for optimum efficiency. Once calibrated, then the carburetor needs attention. IGNITION FIRST, FUEL SECOND. If not interested in the amount of time and experimenting needed, find a shop specializing in performance, with a chassis dynamometer, and spend the the $150.00 or so for a *super-tuning*.

Question from Matt (1981-1983):

Does anyone have any experience with putting a dual exhaust system on 1981 - 1983 Imperials?


From Dan:

OK, on the 81-83 Imperials........or the 80-83 Cordoba/Mirada or even the Diplomat, Gran Fury, 5th Avenue...less we forget this applies to the father of all these cars.......Aspen/Volare...all that is necessary is to move the gas tank one "notch" on the hangers to the right....this way there is room to run pipes in STOCK locations INSIDE the frame to a good pipe bending shop and you have true dual exhaust. At no time are they run outside the rails ala Monte Carlo.........I can send you pictures and detailed instructions upon request. Oh one fringe benefit is the tank now holds more gas since the filler neck is pulled back slightly..........who'da thunk! Does it work you ask..........I have three of my own running around this way!

From Carmine:

I've done this before...

Move the gas tank over one "notch" (notch = indentations made in the tank for the straps) to the right. Their is enough length in the filler neck to allow this, but you'll likely have to lengthen the inlet/outlet hoses on the tank.

I used very discreet, square chrome tips that ended flush with the rear bumper "plastic". I would have to imagine that this is the way the factory might have done it.... had dual exhaust been a status symbol in the 80s, as it was in the 50s-60s.

The same trick works for any F/M/J body.

Question from Neal (1981 - 1983):

Has anyone out there converted their early '80s Imperial to dual exhausts? While on vacation, I'm having some exhaust work done to my Cordoba and have just learned that the Y-pipe and forward catalytic converters are shot. None are available anymore, and my mechanic has suggested converting to dual exhausts with a catalytic converter on each, and then two mufflers, obviously. Is this feasible on these cars? I also suggested fashioning a new y-pipe and omitting the front catalytic converters.  My concern is what unintended consequences might develop by having two tailpipes. I don't think there are the cavities in the floor pan for two rear catalytic converters and mufflers, nor room for an additional tailpipe on the drivers side. How about routing two on the passenger side? 


From Paul:

How much noise do you want to hear? Imperial owners love to keep their cars quiet, but on other vehicles I own I have converted from single exhaust with cats & muffler to dual with dual cats & NO MUFFLERS. The cats keep it fairly quiet except at full throttle where it gets a little bit louder. With a carb (non-EFI like the Imp's) you shouldn't have any adverse effects.

Just a thought. I did it on my 79 Trans Am, 88 Dodge/Shelby CSX and both worked out great. (CSX was a single exhaust, but still lost the cat).

From Dave:

Yes, route together, you can use slightly smaller diameter pipe (the area of each should at least total the area of the original pipe). Your muffler man, as long as he knows area equals radius squared times pi (3.14), can do the figuring (he also has charts). Find another shop if he doesn't have a clue.

Your engine will run better, run cooler, more efficient (higher MPG), more environmentally friendly, produce more power and sound great (a lot of the sound depends on the muffler selected).

Question from Pete:

I've noticed a few messages here about duals. Some are suggesting that the carburetor needs to be re-jetted if duals are installed. Assuming one is keeping the same diameter pipes w/crossover and keeping the same manifolds, why is rejetting necessary? And what are the results if the carburetor IS NOT re-jetted?

Reply from Jack:

OK, assuming the vehicle came from the factory with dual exhaust nothing else would need to be done to the engine after installing low restriction mufflers. However, mine came with a small diameter single exhaust. The carburetor is 'set up' to work with that amount of airflow (hence different specs for dual exhaust in the carburetor manuals). Anything done to improve the airflow will effect the air/fuel ratio. How well the carburetor compensates depends on where the carburetor was at in terms of air/fuel ratio in the first place. If it was a little rich then there should be no ill effects. If it was running on the lean side then you could run into problems such as burnt valves or, worst case, burnt pistons. Mine has developed a slight detonation (spark knock) at WOT that wasn't there before the duals. The initial timing will be backed down 2-3 degrees at a time until it disappears. Now don't assume that this will erase the rest of the gains because right now I'm running about 15 degrees initial (advanced). The factory spec is 10 deg BTDC. Re-jetting the carburetor will come later on after every thing else is completed. Or you could do the 'poor mans' re-jet and raise the float levels a couple of 64TH's. This effectively richens the entire fuel curve. Not very efficient but it works in the short term.

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