Pete here's the pics you requested yesterday. Note that they are both made by HM headers. The 4into1's are built by ford specs and the other by HM. The 4 into 1's the primary pipes are too big (42mm i think from memory) which slows down the air speed and make you lose some bottom end. The cats are also to close. The 4-2-1's have a smaller primary i think it was 38mm or something i'll have to measure it. But there is still no restriction, faster air speed through the pipe which creates a larger vacuum. They give you more low and mid range. I also got better fuel efficiency and a better exhaust note. Dyno results will be posted in a week or two.