I was wondering on the different ways the slant6 has had different duel exhaust setups made. Especially using the original exhaust manifold. On the Dutra Duel I understand that its made to use the rear part of the original manifold for the choke pocket and the front is a special cast.
I have also been seeing where they take the same idea of the Dutra Duel but, keep the front half from the original manifold and adding an exhaust outlet to it. This basically gives you a Dutra Duel exhaust.
What exactly would be the difference between the two? Why couldn't someone just keep the original exhaust in one piece and add the exhaust outlet to the first three runners? Wouldn't this also balance the duel exhaust from the get go? Just curious

The SL6 firing order is 1-5-3-6-2-4 so when you have two seperate manifolds, collecting front 3 & rear 3, you get twice the seperation time between the pressure pulses, the reduces the back-pressure.
You can add a second flange to a factory manifold but it will not give you the seperation as noted above.

Also, think of exhaust gas flow as water would flow, the high velocity gas does not like to take sharp turns so most of your flow would pass right by the added outlet.
DD

Thanks for that information! Now I understand.

What does a 6 into 1 header do for the engine?

Again, time between pulses has a big influence on exhaust system performance. With tube steel headers, you get even more seperation time because each port empties into it's own tube.

The other performance gain factor is in the collector area. When you bring all the individual tubes together into one large chamber, you can create scavenging and pressure wave tuning.
Basically, the momentum of one pulse helps pull the next one along. (or "stack it up", depending on which way the pressure wave is moving)