Header-to-muffler exhaust recommendations, pics appreciated

[MopaR&D]

I have a set of Doug's D-453 longtubes I want to put on my Duster and change up the exhaust in front of the mufflers while I'm at it. Car currently has block-hugger shorty headers with homemade 2-1/4" head pipes going into a Pypes 2-1/2" system with X-pipe. I want to get rid of the X-pipe and run 3" pipes from the header collectors to the mufflers.

First question, how far back do the collectors end on Doug's? I'm trying to get an idea how much distance I have to work with. The mufflers are 26" long Classic Chambered PowerSticks (shaped like glasspacks) and take up quite a bit due to the length. I want the pipes coming off the headers to be as long as possible to get decent secondary tuning length as that boosts torque.

Second, why do all the factory and most aftermarket systems have the mid-pipes bent and running down the center of the chassis? Last few times I was under the car it looked like I could just run them almost straight back from the headers to the mufflers.

I'd love to see some under-chassis pics of your guys' setups for visual aids.

 

[rumblefish360]

There is an episode of Engine. Asters where they run though this exercise. There are a lot of variables to figure on and the best way to do this is dyno the engine while trying different lengths of header collector extensions. That’s expensive!

What the show concluded I’d have to research.

Below are pictures of what the rest of the exhaust should look like. While YOU can not duplicate this because it is on a. Or eggs and your car doesn’t have the real estate available to duplicate, but is shown, you’ll just create a pressure wave cancellation box which simulates an open tube exiting the ex exhaust to the atmosphere. Like what you see on engine Masters, just an open exhaust.

Pressure wave cancellation box shouldn’t number at the minimum the same number of cubic inches the engine is in its size. So an example, if you have a three 60 in.³ motor, each cancellation box should be at least 360 in.³.

After that, the pipe exiting the pressure wave cancellation box can be reduced in size though I don’t suggest it if possible. But it should go into either your glass packs or your mufflers that flow 2.2 in.³ of air per horsepower being made.

This means, each muffler on a 400 hp engine should flow at least 400 CFM. That is a tall order, I know. But a reduction in CFM could very well limit the maximum amount of upper RPM horsepower to be made.

 

[rumblefish360]

If you find it too difficult to use the glass packs under the car, see if they cannot be installed on each side of the gas tank replacing the straight pipe of the tailpipe.

 

[Oldmanmopar]

Mandrel bent turn downs , 2 facing in and weld 2 facing out. You can turn them and keep them tight to the floor and still go through the indents in the torsion cross member. These are 3 1/2 but you can use any diameter. slip fit with connecting tabs and bolts.. the only clamps use were for the hangers at the back of the mufflers . No collector flanges they slip right on the header.

 

[MopaR&D]

There is an episode of Engine. Asters where they run though this exercise. There are a lot of variables to figure on and the best way to do this is dyno the engine while trying different lengths of header collector extensions. That’s expensive!

What the show concluded I’d have to research.

Below are pictures of what the rest of the exhaust should look like. While YOU can not duplicate this because it is on a. Or eggs and your car doesn’t have the real estate available to duplicate, but is shown, you’ll just create a pressure wave cancellation box which simulates an open tube exiting the ex exhaust to the atmosphere. Like what you see on engine Masters, just an open exhaust.

Pressure wave cancellation box shouldn’t number at the minimum the same number of cubic inches the engine is in its size. So an example, if you have a three 60 in.³ motor, each cancellation box should be at least 360 in.³.

After that, the pipe exiting the pressure wave cancellation box can be reduced in size though I don’t suggest it if possible. But it should go into either your glass packs or your mufflers that flow 2.2 in.³ of air per horsepower being made.

This means, each muffler on a 400 hp engine should flow at least 400 CFM. That is a tall order, I know. But a reduction in CFM could very well limit the maximum amount of upper RPM horsepower to be made.

View attachment 1716324986View attachment 1716324985

I have that book, it's actually what first made me aware of the importance of header secondary tuning and collector extensions. Then Engine Masters did their tests which proved it even more. I could just go and use a tape measure to see how much distance there is from the mufflers-forward but I don't know where the collectors would end once the longtubes are in. I don't really want to run a crossover as I'm tired of the sound, reminds me too much of late-model Mustangs/Challengers/Camaros.

I'm not worried about the mufflers being restrictive, they are 2.5" ID all the way through although they do have louvers which impedes flow a little bit. But my 360 would be putting out around 450 HP at best anyway. With the current setup it's closer to 400-420 HP and the shorty headers and small head pipes with tight bends is far from ideal, probably only slightly better than log manifolds.

I know having the pipes bend in and run down the center of the car then bend back outwards to the mufflers would add some length but I intend to fab it up myself from one of those DIY pipe kits so simpler is better, also would be nice to not have anything running under the transmission or driveshaft to make servicing those easier.

 

[rumblefish360]

I have that book, it's actually what first made me aware of the importance of header secondary tuning and collector extensions. Then Engine Masters did their tests which proved it even more. I could just go and use a tape measure to see how much distance there is from the mufflers-forward but I don't know where the collectors would end once the longtubes are in. I don't really want to run a crossover as I'm tired of the sound, reminds me too much of late-model Mustangs/Challengers/Camaros.

I'm not worried about the mufflers being restrictive, they are 2.5" ID all the way through although they do have louvers which impedes flow a little bit. But my 360 would be putting out around 450 HP at best anyway. With the current setup it's closer to 400-420 HP and the shorty headers and small head pipes with tight bends is far from ideal, probably only slightly better than log manifolds.

I know having the pipes bend in and run down the center of the car then bend back outwards to the mufflers would add some length but I intend to fab it up myself from one of those DIY pipe kits so simpler is better, also would be nice to not have anything running under the transmission or driveshaft to make servicing those easier.

Season 5 - Episode 16 from Engine Masters.
It was on the “COVID 350”. It is a .030 over 350 @ 11.4-1 with AFR ported heads, single plane and a 850. Camshaft is (IIRC) 244@050.

The 1-5/8 headers liked the longest set of lengths of the collector extension in which they started out with a Summit 18” extension and welded an additional 12” pipe on for a very long extention.

Both the 30” & 24” extensions made the most torque down low and power up top.

With the pressure wave cancellation boxes, you’ll not need a H or X pipe anymore.
Your current headers are the biggest HP robbers right now.
Where ever the headers collectors end up and the pointed direction they s going, I’m sure you’ll not worry about it all.

I just suggest using the same diameter of collector to the pressure canceling box and the 2-1/2 out is OK.
If the pipe bends are consistent/ mandrel bent, that’s as good as it gets so don’t worry about it.

I have metal ready to go for this exact project. Then my welder stopped working. I don’t have the funds in the “Run account “ to replace it yet.