New header vs. Bisi header, interesting results
The dyno chart is at the end of the video:
Another article that I liked:
Jack Burns, of Burns Stainless, on headers:
"The collector outlet diameter is the most critical dimension in the header. It's what makes the merged collector work the way it does. Each collector we sell is custom-sized to each customer's engine, and there's no real 'formula' to get a broad-based general determination for street machines. As a rule, the overwhelming majority of aftermarket headers designed for the street market have way too big of a collector outlet diameter. Most street guys are losing power because of badly designed, manufactured, or engineered street headers. There is much room for improvement here."
From this article:
The whole point is that everything I know about exhaust systems seems to point to major flaws in almost every header for the D-series I've seen, aside from very high dollar ones that are actually custom made by competent fabricators and designers. These may be the most expensive projects I've undertaken, as I've had to buy a crapload of tools, including a TIG welder just to get to the point I have. But . . . I know it is worth it. I've already learned a ton, and if anything doesn't work, I will learn from that and improve for the next round.
I love that stuff.