Let’s get started.
First thing I did was to make a “wish list” in other words: What criteria do I want to incorporate into my design?
My list is as follows.
1. Headers must allow the use of rear mount A/C unit
2. Headers must be two piece with the only slip together joints present at the collector.
3. Must have descent access to header bolts
4. Must have descent access to spark plugs.
5. Must not have a large primary length difference from one cylinder to another.
6. Must match my MPG Port Plates at the flange.
7. Headers must be easy to install.
8. And most important, they must LOOK COOL!
My headers will be a rifling design where the pulses in the collector rotate in a clock wise or counter clockwise motion. I will mention that I was not able to find a single dyno test comparing a rifling design to a non rifling design. The original GT40 designs that I studied are only rifling on one side.
I am incorporating rifling into my design because I agree with the logic.
Here is a illustration from GT40s .com showing a rifling firing order in the collector. Keep in mind it is not the exact position that is important here it is the order. This order also determines which direction the rotation occurs.
My primaries will be oriented in this order 3258 and 1764
Left-------------Right
8—3 ----------6—4 Top
5—2----------7—1 Bottom
This makes both sides a clockwise rifling motion with the 13726548 firing order.
Given the modest projected power level of 375 emission legal horses for my 400,
my headers will be 1 ¾ primaries exiting into 2 ½ inch collectors.
My car will be a street use only car. No ORR racing or Track events. As such my engine will be built with a emphasis on bottom and midrange power. I feel the added primary length of the 180 design will compliment this goal. I will chassis dyno my car upon completion of its restoration to validate or invalidate my decisions and make the necessary changes.