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Doug Dutra Cast iron headers
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Author:  Adrenalin [ Mon Dec 01, 2008 6:09 am ]
Post subject:  Doug Dutra Cast iron headers
Dear All,

Doug Dutra cast iron headers seems to be easy to build. Does it make any improvement on performance? It looks as if it only doubles the output???

Thanks
Author:  Doc [ Mon Dec 01, 2008 9:50 am ]
Post subject: 
The main advantage to "3 & 3" exhaust manifolds or tube steel headers is from the reduction of back pressure due to increase in "separation time" between exhaust pulses, going into the manifold / header collector.

The next big improvement comes from "scavenging" in a collector, where the flow helps pull vacuum on other idle tubes entering a common area.
The next opportunity is with exhaust length "tuning" where you use the pipe length to help power production in certan RPM ranges.

As for the Dutra cast iron dual manifolds, they take advantage of increased separation time and can have some scavaging if a "Y" pipe is used but they are not "tuned" for a useable RPM range.

As for making a set, yes, you can make your own set if you know how to cut and weld cast iron.
DD
Author:  moparfreak77 [ Mon Dec 01, 2008 4:32 pm ]
Post subject: 
would you recommend a y pipe or go duals all the way back?
Author:  Doc [ Mon Dec 01, 2008 4:36 pm ]
Post subject: 
If you run true dual pipes, most people use an "X" or an "H" cross-over pipe.
For max. scavenging, you can run both pipes into a collector, then run two pipes out of the collector and route those to the rear of the car.
Author:  wvenable [ Mon Dec 01, 2008 4:44 pm ]
Post subject: 
Okay, I understand H and X and even Y. I can even sing the ABC song! But does anyone have a pic of the collector max scavenging doo-gie?
Author:  Doc [ Mon Dec 01, 2008 5:00 pm ]
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Image


Keep the two pipes even in length and they need to end at the same spot inside the collector. The collector should be 10 to 14 inches long.
DD
Author:  wvenable [ Mon Dec 01, 2008 5:13 pm ]
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Doc, thanks for the visual! I think I have seen this before. What are your diameters? If I understand correctly, duals out of the collector? Thanks, Wayne.
Author:  SlantSixDan [ Mon Dec 01, 2008 5:53 pm ]
Post subject: 
Doc, that headpipe is a work of art. If you offered those for sale, I'd buy one!
Author:  64 Convert [ Mon Dec 01, 2008 6:02 pm ]
Post subject: 
Quote:
Doc, that headpipe is a work of art. If you offered those for sale, I'd buy one!
Doc, make that two...and then I'd order another Dutra Dual to make it work.
Author:  moparfreak77 [ Mon Dec 01, 2008 9:05 pm ]
Post subject: 
So why is it better to split the exhaust at the head just to join them later on? What would the difference be between the y pipe and a dual h crossover pipe setup? what about the sound difference? thanks doc
Author:  SlantSixDan [ Mon Dec 01, 2008 9:32 pm ]
Post subject: 
Quote:
Quote:
Doc, that headpipe is a work of art. If you offered those for sale, I'd buy one!
Doc, make that two
Three. I just remembered (duhhh...) I have two slant-6 cars that run right now.
Author:  Joshie225 [ Mon Dec 01, 2008 9:43 pm ]
Post subject: 
Quote:
So why is it better to split the exhaust at the head just to join them later on? What would the difference be between the y pipe and a dual h crossover pipe setup? what about the sound difference? thanks doc
It's better to keep the front and rear cylinders separated just as Doc described. It boils down to keeping high pressure pulses from one cylinder pushing exhaust into another cylinder with lower pressure.

Collecting both sets of three cylinders together downstream costs nothing in horsepower as long as the muffler flows well and saves weight and money over any dual system. Taking weight out of the car, makes it faster.
Author:  GENT [ Tue Dec 02, 2008 9:34 am ]
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Make that 4 Doc.I just started thinking how am I going to get a Y that fits the Dutras when I order them next year :shock: So put me down for one!
Author:  daniel_depetro [ Thu Dec 04, 2008 7:36 am ]
Post subject: 
Quote:
Collecting both sets of three cylinders together downstream costs nothing in horsepower as long as the muffler flows well and saves weight and money over any dual system. Taking weight out of the car, makes it faster.
That maybe true but Doc mentioned having duals coming out of the single collector and running out the rear of the vehicle. No weight/money saved there.
Wouldn't that just be the same as an X pipe on a true dual exhaust?

I am just trying to understand why dual head pipes into a single collector then back to duals again would be better than standard dual exhaust with an X-pipe.
Only advantage I can see is that the head pipes on the one pictured are equal length. This could/should easily be done on a dual exhaust with an X-pipe as well.
Author:  Doc [ Thu Dec 04, 2008 9:54 am ]
Post subject: 
Quote:
...The next big improvement comes from "scavenging" in a collector, where the flow (exhaust pressure waves) help pull a vacuum on other idle tubes, when entering a common area...
The advantage of the Y pipe is to create some scavenging.
To do this, smaller pipes (to get good pulse velocity) enter a larger pipe (a "collector") to help create a low pressure area(s).
Primary pipe sizing, equal pipe length and ending the primary tubes at the same spot, while "hugging" each other, allows a pulse in the "active" tube to set-up a venturi effect in the idle tube next to it.

Collector size and length can be used to help "tune" the RPM range where the scavenging effect is the greatest. Keeping a flat face where the primary tubes enter the collector, helps keep "reflected" harmonic pressure waves from running back up and into the primary pipes. (a small pipe size change, from small to slightly larger, with a square shoulder or "step", in the primary tubes also helps cancel reversion waves in those tubes. ("step headers")

The exit of the collector should have a gradual reduction or "taper" as the pulse wave move out of the collector towards the muffler. (street outlets) Most racers do not mess with this part of the system, they just run the collector diameter out to a "tuned" length and dump the exhaust out there.

For the street, a well designed 2 into 1 system, using a Y pipe "collector area" as described above, gives you a lot of advantages over any true dual pipe system. I suggested splitting two pipes out the back of the collector, only because some owners seemed to be set on running two separate pipes out the back of the car... for "looks" or sound reasons but that arrangement is not ideal for maximum exhaust system performance with inline engines.
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