Quote:
Originally Posted by Madact
('merge spike' in a 2-way merge anyone?) or wall profiles (probably - but not necessarily - bulges along the edges where the tubes 'meet' along the merge) ...
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Due to the inertia of the gasses, I doubt the shape of the spike makes much difference, your probably more interested in gathering the flow up again after passing the other tube. As you noted with the Toyota merge, the primaries in OEM headers tend to be just cut square and inserted into the merge but some do go to a bit of effort after the join, often creating a cone on the start of the secondary rather than just having a straight cut pipe. The shape of the end of the primary will have some effect on reflected pressure waves traveling back down the primary, possibly a straight cut pipe is actually the best for creating those reflected pressure waves. Shaping the start of the secondary to control the expansion into the wider secondary can create a bit of extra suction in the area of the merge. I've not seen much written on this subject, it seems most designs are the result of a good idea followed by testing and normally limited testing due to limited budgets so it may be worth a look at more OEM exhausts as they do tend to have decent testing budgets and the better ones clearly do get things like pipe diameters for each section correct.