Calvin Elston (
www.elstonheaders.com) did a header for a friend of mine, and boy does it work.
1 3/8" od off the head to match the port area for 10" before stepping up 2 more times. Leaving the rest a secret
. Each cylinder displaces ~562cc and is pushing about 60hp through each. revving to 7200rpm. Picked up 10-12% power everywhere over the Stahl based 1 5/8 > 1 3/4" header. Within 2" overall length wise and the same exact Burns collector (2.25" outlet). Also was able to go down a main and an air corrector on a DCOE Weber since the jet signal was much stronger.
Not related to power, it has a bit more crackle than the older header. This is just a warm up run, cut short. Just getting heat into the drivetrain.
https://www.youtube.com/watch?v=y8rVCYFxm8IPaying attention to bend radii is paramount on a header like that. The function of a header is science, but getting large bend radii to fit in tight spaces is the art.
Calvin has a blog, which he hasn't updated in a while unfortunately (
www.exhausting101.com. He also has lots of posts on Speedtalk and Yellowbullet with the username "exhausted". He was the guy who introduced tri-ys back to Cup, and has championships in NHRA, NASCAR, WoO, Le Mans, etc. has a header builder.
One thing he said to keep in mind with the Burns specs - the diameter they give you is what it needs to be at the end of that length. If your port is smaller than that value, you're going to step to get there even though they didn't specify it. The only way you can go with his sizes though is with large bend radii and attention to flow. How he fits what he does in some of the spaces I've seen is pretty extraordinary. Not using a header plate helps a lot (so each tube has it's own flange and the header apart looks like a bunch of single cylinder primaries).
He loves chatting about this stuff. Certaintly worth a call to him to just chat after you get your specs from Burns in hand.
Likely, with your displacement decrease, the exhaust ports are probably way too big to begin with, so best not exacerbate the problem. You’ll still need to step, however.