4-2-1 vs. 4-1 header pt. 2

[markmurray77]

I will hav eto examine it further the next time I have it apart.

 

[70]

Those things are more for the people who have to care about emmsions. Like California I guess. The people who don't want to take it off when the go for testing. I know also that in Ontario they have roadside testing and can take your car off the road right there if it doesn't comply. It all depends on what you are looking for and quite posibly where yo want the power. I also don't hink that the initial stock cat is very restrictive either.

Actually the first cat itself, flows realtively well for a cat. Corky tested it while he did the intial development of the BEGI/FP turbo.

The problem lies in the entrance to said cat, and the exit. Mainly the exit on the stock exhaust is less than 1.75" inside diameter. That doesn't help flow at all.

Decent gains were made by changing out the "down pipe" from the first cat to the second and by making the exit of the first cat larger. Making the entire exhaust, from the first cat back, 2" ID like it is said to be from Mazda makes a huge difference.

However, removing the first cat entirely will flow better than keeping it there and making the exit and down pipe bigger.

But the option does exist to keep the first cat and improve flow. It just requires some custom work to make it work.