You can always dig up something that goes against anything.I can tell you every nascar has stepped headers,they make more power PERIODI guess this explains it?:
"One of the more interesting tests we did while preparing at the dyno, was to run a set of 1.75" Kook's with a 3" collector VS. a 1.75" to 1.875" stepped Kook's with a merged collector. The difference in scores between the two headers was 1-2 points at best; that is 2 points out of 1,000. I've never been convinced that stepped headers or merged collectors make more power, and this test reinforced my beliefs. The two headers did have differing peak numbers, but peak is the false god...average is the true strength of the engine. Stepped headers and merged collectors are expensive. If merged collectors work, why do they work? It's my belief that they work by simply reducing the size of the collector (people choose collector diameters that are too large)."