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I haven't read all the posts, and it's not my place, but aren't those headers very, very small in terms of collector diameter and length?



Those are merged collectors and you typically want a lesser difference between the primary tube size and the collector outlet or what is called the pinch. After the pinch you will have a megaphone or a tapered cone up to a normal bigger size. Those headers are 2-1/8" primaries (at the collector) and the pinch is 2-1/2 or 2-3/4" and then it goes back up to 3" and then it goes up to 3-1/2" right after the V-Band ring (in the secondary exhaust). Since this is an A-Body and I have 2-1/8" primaries the collector placement was very critical just to get them to fit and give me any kind of ground clearance. I ended up adding a couple inches of 3" just to get the pinch to align with the crossmember. As it is , it turned out very well.

Here is a pic of the smaller header collectors that were on the Crate motor I just took out of the car. You can see the pinch and then the cone bringing it back up to 3-1/2" just past the V-Band clamp. Those headers have a 1-7/8" primary at the collector. You can see how tight everything is and keep in mind the primaries on the 501 headers are a Quarter inch bigger X 4!

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