Next came the headers. When I started racing, I got a set of headers on eBay that I thought were uprights...the guy had them listed cheap, I asked if they were uprights and he told me yes. Well, they weren't. They were a set of circle track headers that had very short 1 3/4" dia. primaries into a 3 1/2" colllector. I ended up running them for a while, but I welded on a turn-out so they would quit filling with water when it rained.
I decided it was time to build a set of headers tuned for this engine. I looked online at several calculators, which take where in the rpm band your peak torque is, what primary size you are using, and what collector size you are using, and gives you lengths of each. With my collector and primary size, the calculator came up with about 31" on primary length and (IIRC) 18" on collector length.
I started building the headers by cutting off the current collectors.
Here's the cut off collector end.
At this point, I bolted the cut-off headers back onto the engine so I could build out the rest of the headers. I got a box of 1 3/4" mandrel bends off of eBay.
With a general picture in mind of what I wanted, I started cutting tubing, and mocking them up together, then kept taking the headers back of to tack things in place. I used a sharpie to mark reference lines.
With all 4 45 degree elbows tacked in place, I mocked this side up one more time to check fitment.
From there, I mocked up a 90 degree elbow to kick back toward the rear. From there, I removed the headers to tack all 4 tubes in place.
All tacked together, less the collector.
All 4 tubes fit together quite well.
From there, I have to weld all 4 tubes up solid. There's two ways this could be done. I could have either separated all 4 tubes away from the header flanges, or I could split the flanges apart and hope they go back together squarely. I went for option "B" this time.
For the two center tubes, I took my sawzall and cut most the way through the flange, then pulled it apart by the tubes, so I'd have enough room to weld all the way around them.
After all 4 tubes were welded up solid, I brought back in one of those junk heads to use as a jig to hold the header flanges together.
Flanges welded back together.
Now came time to check fitment of the final product. Well, before I put the collector on, anyway.
Then fitting up the collector.
Just don't forget -- when you're building your own headers, you must put a little square piece of sheet metal between the 4 tubes at the collector so you don't have exhaust leaks between the tubes. It should go in the empty space in the middle of all 4 tubes shown here:
Here's some video of each set of headers with the same engine/cam setup. In both videos, please don't mind all the junk around all over the place...Y'all know how projects go!
Before, with the short headers:
http://www.youtube.com/watch?v=CIOK4vmuBOc
After, with the custom headers:
http://www.youtube.com/watch?v=U8ar-4qwnTE
One of the main things I was happy about was the fact that the longer headers got rid of the pop after the rev.
EDIT: anyone know why I can't put a youtube vid in the post? I can only put the link there...