Obviously it would be nice to have actual numbers on 1 5/8 vs 1 7/8 headers. 20 or more is enough for me to say it’s worth the money. Trying to squeeze out every tenth I can.
I may have already replied to this but I don't think you're going to see 20 horsepower going from a header to a slightly bigger header. Especially with 3" exh already, i look else where.
