[greg schroeder]

Originally Posted by wanab5150

I went to Stevens shop in Reno today and checked out both the 402 headers and a set of the older style that came off another car. I took some close-up photos to analyze.

I took the old used headers and separated the mass which is blocking the port and in Photoshop superimposed that mass inside the existing port of the header. I placed a 1/32' grid over the entire exhaust port. Not being a math whiz, I simply counted the square grids in the blocked mass and inside the open portion of the port, subtracted the blockage from the open port and came up with a 38% blockage over the 402 headers for the Roush/AFR heads.

If you look closely at the port in the old headers and VISUALLY move the burnt portion on the flange into the open port you will realize this is pretty accurate. And they told me I needed to redo Algebra in Summer school!!! Screw'em!

Taking into consideration that there is a huge blockage (over a third)and the fact that the spent gasses are rebounding off the blunt wall of the flange and having to compress over and over again trying to fight their way out, these older headers are suppressing loads of HP in your big inch motors.

Think of shooting a .45 round inside a 6'x6'x6' steel cube. It will ricochet over and over until it loses velocity…….or escapes. Thank God gasses compress, or the heads would have been blown into orbit as soon as it was fired up the first time.

I will say it again.....If you are running the old headers you might as well leave the 2 inch mufflers on your Superformance. The 3" mufflers may sound better but performance CAN'T really change much. If you have the 402 headers and the 2 inch mufflers it's like putting a golf ball in a garden hose! Bye Bye 100 ponies!

Do you know the width and height of the inlet on the 402 header?