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Dual exhaust

Chad Witham

Chad Witham

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Can you guys post pics of the location where your dual exhaust dumps under the rear bumper? I bought the Flowmaster tailpipe kit and I want ideas before permanent mounting.
 
On what? With what exhaust, engine and half a million other questions to follow this post.
 
mopar 3 B said:
On what? With what exhaust, engine and half a million other questions to follow this post.
Click to expand...

Well,... he posted it in the '71 -'74 Mopars section on ForBBodies only, so I'd say it's probably pretty safe to assume it is a 71-74 Charger or Road Runner, and the title of the post is "Dual Exhaust" so I'm guessing it has a V8 in it of some sort. Do we need more specifics to show where people's exhaust comes out under the rear bumper?

I don't have a 71-74, so I did a quick search to see what I could find for you. Surprisingly I wasn't able to find as much as I thought. Here's what I did find...

Charger exhaust.jpg Charger.jpg 522031.jpg hqdefault.jpg imagesJN4JVEE6.jpg p39589_large-1971_Plymouth_Road_Runner-Rear_View.jpg Road Runner.jpg R-T_rear.jpg
 
FrnkNsteen said:
Well,... he posted it in the '71 -'74 Mopars section on ForBBodies only, so I'd say it's probably pretty safe to assume it is a 71-74 Charger or Road Runner, and the title of the post is "Dual Exhaust" so I'm guessing it has a V8 in it of some sort. Do we need more specifics to show where people's exhaust comes out under the rear bumper?

I don't have a 71-74, so I did a quick search to see what I could find for you. Surprisingly I wasn't able to find as much as I thought. Here's what I did find...

View attachment 747342 View attachment 747343 View attachment 747344 View attachment 747345 View attachment 747346 View attachment 747347 View attachment 747348 View attachment 747349
Click to expand...


Good call. Yes its a 73 Charger with a 318. It currently has some poorly cobbled together duals that dump just in front of the axle.

As to the other posters question of what exhaust, well it has Heddman 1 5/8" headers that I am keeping past that it is all gonna be new. I have a pile of new parts including new mandrel "S" bend exhaust collectors (18" long in case you need that info), some Dynomax Race bullets (16.5" long), 10' of straight pipe and a tailpipe kit from Flowmaster for B-body MoPars (not sure how long the are but they are one piece and run from the bumper +4"'ish all the way to in front of the axle somewhere under the back seat). Also it's all 2.5" pipe. If you need more info feel free to ask.
 
2.5 inches on a 318 might be a bit big if stock or even slightly modified. Will be a big bottom end loser. 2 inch may have been a better choice.
 
mopar 3 B said:
2.5 inches on a 318 might be a bit big if stock or even slightly modified. Will be a big bottom end loser. 2 inch may have been a better choice.
Click to expand...

I appreciate your input and all but unless you have pics to show what I asked please keep your opinion to yourself. I didn't ask for input on what size exhaust I need. I'm not providing every spec to every part of the car for you to review. I know the engine, trans and rear combo I have and I am comfortable with the exhaust size I chose.
 
Last edited:
Charger72 said:
If you do a search for some of Tim Wellborn's Chargers there are some shots floating around of various exhaust tips. This FC7 look at the rear shot and you can enlarge the pic.
https://www.mecum.com/lots/FL0119-363708/1971-dodge-hemi-charger-rt/

https://www.mecum.com/lots/FL0115-204115/1971-dodge-hemi-charger-rt-pilot-car/

https://www.mecum.com/lots/FL0117-269939/1971-dodge-hemi-charger-rt/
Click to expand...

I don't know who that guy is and those links/images sure didn't come up in my google searches. Although my wife tells me my googlefu is weak
 
So basically what I think I'm seeing is the exhaust pipes exit under the car from either under the frame rail or just inside of it. Is this correct?
 
I guess he has the biggest collection of 1971 Hemi Charger R/T's around. Plus a lot of other amazing Mopars and non-Mopars.
 
Looks to me like personal preference.
If it's my car ill do what pleases me
 
Chad Witham said:
I appreciate your input and all but unless you have pics to show what I asked please keep your opinion to yourself. I didn't ask for input on what size exhaust I need. I'm not providing every spec to every part of the car for you to review. I know the engine, trans and rear combo I have and I am comfortable with the exhaust size I chose.
Click to expand...

Wow! Bit of attitude there! Mopar 3 B wasn't giving you crap and I thought his response was value added. He was just sharing his opinion that you might get better torque response with a slightly smaller pipe if running a 318, and I agree with him. It's not like he said "What the hell were you thinking going with 2.5"? That was stupid!!" All he said was that it would lose bottom end torque.

If you have already purchased your components and choose to stick with them, that's up to you, but there's no reason to be rude! Don't get me wrong, I understand he probably irritated you with his initial response, but what's the old statement "Two wrongs don't make a right". Guess I get tired of the bickering that seems to be getting more common lately.
 
Last edited:
FrnkNsteen said:
Wow! Bit of attitude there! Mopar 3 B wasn't giving you crap and I thought his response was value added. He was just sharing his opinion that you might get better torque response with a slightly smaller pipe if running a 318, and I agree with him. It's not like he said "What the hell were you thinking going with 2.5"? That was stupid!!" All he said was that it would lose bottom end torque.

If you have already purchased your components and choose to stick with them, that's up to you, but there's no reason to be rude! Don't get me wrong, I understand he probably irritated you with his initial response, but what's the old statement "Two wrongs don't make a right". Guess I get tired of the bickering that seems to be getting more common lately.
Click to expand...


I wasn’t all trying to give attitude (not sure how you derived that from typed words) however I know the engine and what’s been done to it and I already have the components.

I merely asked for pics of where dual exhaust exits under the body not a critique of my parts selection.
 
mopar 3 B said:
On what? With what exhaust, engine and half a million other questions to follow this post.
Click to expand...
Simple question in, simple answer out.

mopar 3 B said:
2.5 inches on a 318 might be a bit big if stock or even slightly modified. Will be a big bottom end loser. 2 inch may have been a better choice.
Click to expand...

I’ll bet you cash this is incorrect.

FrnkNsteen said:
Wow! Bit of attitude there! Mopar 3 B wasn't giving you crap and I thought his response was value added. He was just sharing his opinion that you might get better torque response with a slightly smaller pipe if running a 318, and I agree with him. It's not like he said "What the hell were you thinking going with 2.5"? That was stupid!!" All he said was that it would lose bottom end torque.

If you have already purchased your components and choose to stick with them, that's up to you, but there's no reason to be rude! Don't get me wrong, I understand he probably irritated you with his initial response, but what's the old statement "Two wrongs don't make a right". Guess I get tired of the bickering that seems to be getting more common lately.
Click to expand...

Disagree. It all depends on how text is read given the tone of the text. It is t easy assigning a tone (voice/attitude) to text. I do t think he was wrong. If fact, I agree. The quest was simple and not answered but the question was questioned.

Chad Witham said:
I wasn’t all trying to give attitude (not sure how you derived that from typed words) however I know the engine and what’s been done to it and I already have the components.

I merely asked for pics of where dual exhaust exits under the body not a critique of my parts selection.
Click to expand...

Majorly agreed! 1,000%!!!!

You ask a simple question and everything else gets turned around and critiqued, judged and picked apart. Not to mention it has zero bearing on the question.

Good luck with your build.
 
Chad Witham said:
I wasn’t all trying to give attitude (not sure how you derived that from typed words) however I know the engine and what’s been done to it and I already have the components.
Click to expand...

I guess when someone says "please keep your opinion to yourself. I didn't ask for input on what size exhaust I need." it comes across to me as having an attitude.

That being said.... I can understand where you are coming from. If you already have all the components, I'd stick with them and see how it does when you get it all together. Any slight differences in power between the two may not even be noticeable with your butt in the seat.

As for if a larger diameter exhaust can negatively affect low end torque, I've personally seen it, and have read it from multiple sources, such as this snippet:
A larger exhaust changes the shape of the power curve. It makes it more peaky, but the area under the curve is reduced. Average power is less but peak power is more. This will present as an extra couple of kW of peak power on a dyno run as it provides lower resistance at peak exhaust volume. However, looking at the entire rev range, the larger exhaust has deviated from the optimal size and average power over the full rpm range will be reduced. Maximum torque may be less and low rpm will produce less power. Fuel efficiency will also be worse, since most of the time your engine operates in the bottom half of its rev range.

In my case,... my Barracuda (400 4spd) had 3" exhaust coming off the headers and dumping right before the rear differential. Once I got it on the road, I had a local shop put in on the chassis dyno and tune it in. I didn't like the exhaust dumping under the car and the drone I was getting, so I replaced the 3" with 2 1/4" and ran it all the way out the back (3" wouldn't fit over the axle and between the shocks and gas tank).

I took it back to the shop to have them put it back on the chassis dyno to see if I lost any power and re-tune as necessary. Turns out power and torque went up with the smaller exhaust on the lower half of the power curve, with no significant loss on the high end. The difference wasn't big, and couldn't really tell a difference while driving (other than the 1500-2200 RPM drone was gone), but on three pulls, it was consistently higher than the previous runs.
 
And this helped how? In the search for pictures?
:rofl:

FrnkNsteen said:
I guess when someone says "please keep your opinion to yourself. I didn't ask for input on what size exhaust I need." it comes across to me as having an attitude.

That being said.... I can understand where you are coming from. If you already have all the components, I'd stick with them and see how it does when you get it all together. Any slight differences in power between the two may not even be noticeable with your butt in the seat.

As for if a larger diameter exhaust can negatively affect low end torque, I've personally seen it, and have read it from multiple sources, such as this snippet:
A larger exhaust changes the shape of the power curve. It makes it more peaky, but the area under the curve is reduced. Average power is less but peak power is more. This will present as an extra couple of kW of peak power on a dyno run as it provides lower resistance at peak exhaust volume. However, looking at the entire rev range, the larger exhaust has deviated from the optimal size and average power over the full rpm range will be reduced. Maximum torque may be less and low rpm will produce less power. Fuel efficiency will also be worse, since most of the time your engine operates in the bottom half of its rev range.

In my case,... my Barracuda (400 4spd) had 3" exhaust coming off the headers and dumping right before the rear differential. Once I got it on the road, I had a local shop put in on the chassis dyno and tune it in. I didn't like the exhaust dumping under the car and the drone I was getting, so I replaced the 3" with 2 1/4" and ran it all the way out the back (3" wouldn't fit over the axle and between the shocks and gas tank).

I took it back to the shop to have them put it back on the chassis dyno to see if I lost any power and re-tune as necessary. Turns out power and torque went up with the smaller exhaust on the lower half of the power curve, with no significant loss on the high end. The difference wasn't big, and couldn't really tell a difference while driving (other than the 1500-2200 RPM drone was gone), but on three pulls, it was consistently higher than the previous runs.
Click to expand...
 
FrnkNsteen said:
I guess when someone says "please keep your opinion to yourself. I didn't ask for input on what size exhaust I need." it comes across to me as having an attitude.

That being said.... I can understand where you are coming from. If you already have all the components, I'd stick with them and see how it does when you get it all together. Any slight differences in power between the two may not even be noticeable with your butt in the seat.

As for if a larger diameter exhaust can negatively affect low end torque, I've personally seen it, and have read it from multiple sources, such as this snippet:
A larger exhaust changes the shape of the power curve. It makes it more peaky, but the area under the curve is reduced. Average power is less but peak power is more. This will present as an extra couple of kW of peak power on a dyno run as it provides lower resistance at peak exhaust volume. However, looking at the entire rev range, the larger exhaust has deviated from the optimal size and average power over the full rpm range will be reduced. Maximum torque may be less and low rpm will produce less power. Fuel efficiency will also be worse, since most of the time your engine operates in the bottom half of its rev range.

In my case,... my Barracuda (400 4spd) had 3" exhaust coming off the headers and dumping right before the rear differential. Once I got it on the road, I had a local shop put in on the chassis dyno and tune it in. I didn't like the exhaust dumping under the car and the drone I was getting, so I replaced the 3" with 2 1/4" and ran it all the way out the back (3" wouldn't fit over the axle and between the shocks and gas tank).

I took it back to the shop to have them put it back on the chassis dyno to see if I lost any power and re-tune as necessary. Turns out power and torque went up with the smaller exhaust on the lower half of the power curve, with no significant loss on the high end. The difference wasn't big, and couldn't really tell a difference while driving (other than the 1500-2200 RPM drone was gone), but on three pulls, it was consistently higher than the previous runs.
Click to expand...

Was your 400 stock?

My 318 is most definitely not stock or even a mild build. I have all the specs of it. It is built similarly to Steve Dulcich’s 400 hp 318 build he did in Hot Rod magazine. It also has a built 727 and a 3.55 8 3/4 rear. If and when we swap the 318 I will for sure not have to change the exhaust.

With the Dynomax race bullets I am expecting some drone the Flowmaster Tailpipe Kit should help some with that though.

My 451 has 3.5” exhaust on it. I also had 3” exhaust on a stock AMC 360. It’s all a personal preference and I’d rather it flow than be choked up. I’ll surrender some bottom end as it had plenty with the junk exhaust I removed.

FrnkNsteen I appreciate your pics you posted. They gave me enough info to figure out what I needed.
 
25D1072E-28AE-4E48-BB10-60AEECE97B00.jpeg
CF76C52D-9374-4CAF-9DC9-2D2D645CD37E.jpeg
0543722E-AAF6-47EA-990F-3A8EC8BB9C49.jpeg


This is what’s getting replaced. All 2” and nasty.

I’ll post pics of the new stuff as soon as I finish hanging it.
 
Chad Witham said:
Was your 400 stock?

My 318 is most definitely not stock or even a mild build. I have all the specs of it. It is built similarly to Steve Dulcich’s 400 hp 318 build he did in Hot Rod magazine. It also has a built 727 and a 3.55 8 3/4 rear. If and when we swap the 318 I will for sure not have to change the exhaust.

With the Dynomax race bullets I am expecting some drone the Flowmaster Tailpipe Kit should help some with that though.

My 451 has 3.5” exhaust on it. I also had 3” exhaust on a stock AMC 360. It’s all a personal preference and I’d rather it flow than be choked up. I’ll surrender some bottom end as it had plenty with the junk exhaust I removed.


FrnkNsteen I appreciate your pics you posted. They gave me enough info to figure out what I needed.
Click to expand...

Nope,.... not stock, but not the level of build you have in your 318 either. Sounds like you have a pretty healthy build! Had no idea you had that much into it. Your posts earlier just said you have a 318. Sorry to question you then! You're on it.

How do you like your 451? I have been contemplating doing a 451 build. I have a spare 400 block as well as another complete 400 engine, a 440 steel crank, and a couple sets of 400 and 440 connecting rods. It would be fun to build something on the side to swap out with the 400.

No worries on the pictures. I had some time to look around a bit and thought I'd share what I found. Looking forward to seeing how it all comes out!
 
Last edited:
rumblefish360 said:
And this helped how? In the search for pictures?
:rofl:
Click to expand...

It's called a conversation Rumblefish! Isn't that what we are here for?

If you look above in the thread, I was one of only two people that actually did post pics of 71-74 Mopar exhaust as was asked.
 
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