MWS equal-length headers for a 3.4L DOHC (especially on a Fiero)

I designed these headers with Don Jeffer's help--and got additional help as well from Jerry Heimbecker and Daryl Armstrong, who taught me to weld. Refer to the Intake page to see how this all works in concert to help the DOHC, with it's huge valves, ports, throttle body, get as much from a Naturally Aspirated setup as is humanly possible, and still be streetable. This motor is a 1996 Chevy 3.4L DOHC with the larger intake and exhaust ports. The shape of the exhaust ports being a special challenge.

The port size is about 2.6" wide by 1.1" tall. I ended up using tubing that was 1.75" OD as my primary tubing, it's about 1.63" ID. (16 guage). I decided to use the total valve area of the two valves, NOT the port shape, and area as my guide for what size tubing to use. So, the tubing is smaller in total area than the exhaust port face. The special problem I was faced with was: most unusual shaped header starter tubes can come straight out the motor for an inch or two, then start doing their curving, or neck-down in size, or whatever. The engine bay is large enough to allow this. So, you could conceivably buy some 2.5" to 1.75" cones, and smash them into ovals on the large side, and just use that to go from the oval shape to the smaller, rounder tubing.
Fiero compartments being as cramped as they are, I had to be able to come out as an oval, immediately begin to turn, AND go downward, AND neck down to smaller tubing, AND go from an oval to a round tube....all at once!!
I had to make curving "horns" that flowed, gathered the two valve's exhaust and did their curves, w/o having jagged edges or sudden differences in size. I acheived this by slicing the tubing down the middle, and stretching it open to meet the oval shape, then welding in two pie-shaped pieces that were painstakingly cut to fit and weld tightly, with the open cuts I made. Some of these pieces had to curve and drop and swoop, as they conformed to the bends I was using.

When the project was over, I saw this picture of some Fiero headers that Doug Chase had bought hand-made from a guy, and my jaw dropped. This was exaclty what I was GOING to do: route everything "Fiero style", and have them both meet by the cat, and route as a single-exhaust system around and to the back--to meet a single muffler.

Instead, I decided to do everything as "by the book" as I could, just for the sake of "trying" to be optimum. Don was encouraging me to do a truly dual exhaust--no balance pipe (of course, the firing order does not call for it) and two mufflers. I began designing the system to route like this.

The idea being that both banks culd exit out the back, and somewhere, somehow, I'd stuff some mufflers in there.

Here's how they ended up:

You may notice that the tubing is tighter and less spread out than in the fabrication-stage pictures. After taking those first pics, I found ways of tightenting up the groups and still maintaining the equal-length nature of the project. Only one tube varies--by design--in order to get past the Knock sensor on the 1-3-5 side. It's about 1.5" too long. When you blow into these babies, 5 of these tubes make the same note!!

The O2 sensor only goes into one bank, and is the heated variety (4-wire). I found that having the O2 so far away from the hot ports, made it cool down enough that the motor would go into open loop at idle, all the time.

here's the setup "actually" fitting into the Fiero's tight engine bay, still leaving room for me to check my tranny oil.