Quote:
Originally Posted by tjts1
AutoZine Technical School Article
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With respect to many 4-cylinder engines produced in the last 10-15 years, valve overlap has proved to be quite common -- also the compact (and likely inexpensive) design of the 4-1 header is often bolted to these blocks. I recall during my "not-so-Eco-Modding" days that the 4-2-1 header was advertised as one of the first places to start with improving performance (especially in the Honda B-Series) -- whether that can be Scientifically backed, is another question.
The question then becomes, would a specifically tuned 4-2-1 header offer appreciable FE gain for the average inline-4, without any other mods to increase compression?
-RH77