New Dual Exhaust

[PontiacJim]

Yes.

That's what I thought. It gets a little scientific and I am by no means a science guy. What it boils down to is "pressure waves" created by the exiting of the burned exhaust gases - and these can change with temperature.

High pressure exhaust gases exiting the cylinders sets into motion a pressure wave (somewhere about 1700 feet per second) that travels down the entire length of the exhaust pipe/system. The positive pressure wave is reflected at the open end of the exhaust pipe (like the sound wave in an organ pipe) and a negative expansion wave of low pressure travels back along the pipe towards the cylinder. If the wave arrives while the inlet valve/port is open, it will enter the cylinder and create a "depression" which aides in cylinder filling. If the wave arrives while the cylinder filling process is over, it can displace some of the cylinder charge and reduce cylinder pressure before the compression stroke which reduces power from that cylinder.

This process is significantly important on multi-cylinder engines (ie V8's). Not only does the timing of the expansion wave influence the charging process, the positive pressure wave is important. If 2 or more valves/cylinders are open to the exhaust pipe at the same time, the positive pressure wave from one cylinder can cause exhaust gases to return to the other cylinder and create a back pressure to force out the incoming air/fuel mix from the intake.

Using a larger diameter exhaust pipe can eliminate or minimize the effects of a pressure wave. On the other hand, the pressure wave can be used as a tool when pipe diameter and pipe length are fitted (ie headers) to optimize the wave to aide in filling the cylinder.

Bottom line: larger pipe can increase better flow/horsepower.

 

[73Coupe]

It's finally happening! After many flubbed appointments due to knee problems and resulting backlog of work, the shop is finally clear again for new projects. I dropped the car off this morning. 2.25" will be the pipes, Todd suggested that over 2.5" for a quieter sound. I will hopefully be posting photos of the completed project on Monday.

 

[73Coupe]

It's finally in!

Tips done perfectly, and terminated inward a bit to insure adequate room for future hitch. I might extend them back further pending how the hitch turns out...

View looking back from transmission area.

Left side exhaust pipe from manifold. He routed it just right, although it's too close to the bottom of the firewall so it comes into contact with the body under hard acceleration.

Right side pipe.

Rear view.

 

[73Coupe]

My only complaint: too loud/resonance/drone under low speeds, idle, and part throttle. Loud outside too. Lots of resonation in the car. It sounds like I'm driving a Winnebago.

At highway speeds, though, they are nice and quiet. You can really feel the power increase at higher RPMs.

He installed Walker 17824 Sound FX mufflers. 21" body length.

For this car (and all C-bodies), the Walker catalog calls for #18381, which according to them is the same type of construction, just 4" longer. These are non-insulated mufflers and definitely "ting" when you rap them with a knuckle.

The Walker tech line guy recommended #21063, which is about 22" body length and their "Quiet Flow" line. It is SS construction.

For all of you who have had dual exhaust installed, what mufflers did you use and how do they sound?

I feel that it should sound like a sporty luxury car, understated power until called upon. Does that make sense?

 

[CBODY67]

For general principles, you might try advancing the base timing a few degrees and see if the low speed issues change.

Several years ago, one friend had a '69 Dart GT340. He got some mufflers for it, based on flow, and it was too loud to talk over inside the car. Another friend had a 444+6 Road Runner, with some Walkers on it. Reasonably loud, but not as loud ad the Dart. They swapped mufflers and BOTH cars got quiet and sounded good.

The pics of that system look great!

CBODY67

 

[75LandYacht]

I used Flowmaster delta 50’s on my 75 / 440. Typical Flowmaster sound, they sound great at highway speed, you can’t even really tell that they’re on there, but at around town speeds you know they’re there, mild drone inside the car but not bad. they do sound a but “Tinny” to me though. I may change them out later for something a bit quieter..

 

[CBODY67]

There is a "Flowmaster sound". When they first came out, they were the latest/greatest thing to happen to mufflers. As things evolved, every Mustang 5.0L had to have them if the owners were to have credibility, it seems. I got to where I could hear them coming, later coming to "not like" that sound. But that is a part of the Gen I Mustang 5.0L culture, it seems, which I appreciate and understand. I now take note of it and go on, but would look for something with similar flow and a quieter sound on my cars. I found a muffler flow chart at www.bigblockmopar.com the other day.

CBODY67

 

[Big_John]

My only complaint: too loud/resonance/drone under low speeds, idle, and part throttle. Loud outside too. Lots of resonation in the car. It sounds like I'm driving a Winnebago.

At highway speeds, though, they are nice and quiet. You can really feel the power increase at higher RPMs.

He installed Walker 17824 Sound FX mufflers. 21" body length.

For this car (and all C-bodies), the Walker catalog calls for #18381, which according to them is the same type of construction, just 4" longer. These are non-insulated mufflers and definitely "ting" when you rap them with a knuckle.

The Walker tech line guy recommended #21063, which is about 22" body length and their "Quiet Flow" line. It is SS construction.

For all of you who have had dual exhaust installed, what mufflers did you use and how do they sound?

I feel that it should sound like a sporty luxury car, understated power until called upon. Does that make sense?

IMHO, a lot of that drone is caused by your pipes being too short. The exhaust resonates under the car... basically hits the pavement and bounces back up. I had an issue like this with my '70 300 vert when I first bought the car. Ultimately, I replaced everything with a TTI setup, but the short term "get me through the summer" solution was a cheap, short glasspack muffler added to the end of the pipe with the tip extending out to the edge of the body.

Another improvement to the sound, and one that Chrysler did with their high performance B-bodies, would be an H pipe connecting the two pipes.

I've had a couple C-bodies, including a '73 NYB, with class III hitches and never had to shorten the pipes. They can be moved slightly outboard if needed, but the custom fit hitches I used to buy missed the pipes nicely.

 

[commando1]

That is improperly hung. That would be considered a solid mount by most standards. Practically zero flex in snubbing out vibration.

 

[73Coupe]

Improperly hung...even with the rubber block? I don't think I've had any vibration problems (that I know of yet).

 

[73Coupe]

IMHO, a lot of that drone is caused by your pipes being too short. The exhaust resonates under the car... basically hits the pavement and bounces back up. I had an issue like this with my '70 300 vert when I first bought the car. Ultimately, I replaced everything with a TTI setup, but the short term "get me through the summer" solution was a cheap, short glasspack muffler added to the end of the pipe with the tip extending out to the edge of the body.

Another improvement to the sound, and one that Chrysler did with their high performance B-bodies, would be an H pipe connecting the two pipes.

I've had a couple C-bodies, including a '73 NYB, with class III hitches and never had to shorten the pipes. They can be moved slightly outboard if needed, but the custom fit hitches I used to buy missed the pipes nicely.

Good info. Once I get a hitch I will probably move the tail pipes as rearward as possible. I am going to build a hitch setup like Will did on his 'Jezebel'.
Going to add an H-pipe too. I requested this and he forgot.

 

[commando1]

Improperly hung...even with the rubber block? I don't think I've had any vibration problems (that I know of yet).

Then it's fine.

 

[73Coupe]

Then it's fine.

Phew! What's up with the Arabic?

 

[commando1]

It's Farsi.

 

[Ripinator]

It's Farsi.

Linky no worky. . .

 

[73Coupe]

Wow. it worked...

 

[live4theking]

Nice looking system.

 

[Keith926]

Nice job for sure. I bend exhaust as part of my glorious job of an auto mechanic. It can be hard to get a system bent the first time on a vehicle you’re not familiar with, even giving due diligence, example being your rub issue under acceleration, seeing the craftsmanship on the job I’d guess you’re guy would make that right free of charge.

I have only done big block Mopar exhaust on my 72 Newport so I’m not as versed in muffler choices as I am with late model pickups or 73-87 Chev trucks, it’s a curse of the times. If you have been around some 80s era one tons think of the way the tow truck or landscape dumper makes your ears pop, I think that is the kind of drone you’re getting, it’s a similar muffler to those trucks you have on your car. Up here in Canada I can’t get a SS quiet flow in that configuration, it is possible that it would have less drone, maybe not worth the extra cost. If it was me I would try adding a small glass pack or baffle pack inline where it fit best if you want quiet. Maybe try a super turbo kinda muffler if you want a bit more noise. Flow masters I think would be a bit loud for what you want.

It can take some trial and error to get it just right, there are so many variables when it comes to the an individual’s right sound. One can think there car will sound just like another but things like car A was a 69 and car B was a 74 so you’re talking a decent power motor to a smog motor, different manifolds or headers, even a muffler on one that’s older so slightly different design, it can be a wild goose chase getting it right but it’s all a part of the game.

I use the same hangers as you have, it’s not original but they are the best option available to exhaust fabricators. They are more rigid than most original hangers and I’ve run into vibration issues from having too many, all part of the fun.

 

[73Coupe]

Then it's fine.

Well a couple weeks and about 1000 miles later, it's now vibrating from somewhere in the rear, at idle. Not a pleasant sound.

I'm still waiting on the walker quiet flows to arrive at the muffler shop, so when I have those swapped in I will have him address the vibration and possible re-hang the tails if deemed at fault. I'll tell him that a hothead from Fumbuck Iran called it out, haha.... نادرست آویزان شد

 

[cantflip]

Well a couple weeks and about 1000 miles later, it's now vibrating from somewhere in the rear, at idle. Not a pleasant sound.

I'm still waiting on the walker quiet flows to arrive at the muffler shop, so when I have those swapped in I will have him address the vibration and possible re-hang the tails if deemed at fault. I'll tell him that a hothead from Fumbuck Iran called it out, haha.... نادرست آویزان شد

That's Fumbuck Florida... Iran has oil