In my quest for a faster and more efficient R series engine, I have finally
come to the exhaust. My research has brought me to the following (Short
version):
The stock manifold was "sort of" a 4-2-1 (tri-Y) design.
All of the headers I've seen are 4-1 design.
Popular theory has the 4-2-1 being better in the low to mid rpm range and 4-1
better at the high end with a narrower power band, although a "merge"
collecter can widen this somewhat.
Length and diameter of the tubes are critical in getting the max power in the
RPM range you want for both header designs. Longer tubes for low-mid range,
shorter tubes for high rpm.
Too small diameter gives good low range responsiveness, but chokes the engine
at higher rpm.
Too big a diameter gives you a sluggish engine that may or may not work well
at higher rpm.
What I have read brings me to the concusion that a 4-2-1 header can provide a
quieter, more responsive, and powerful engine.
The standard design pairing 1&4 and 2&3 puts the cylinders paired at 180 deg.
apart for maximum scavenging, aiding what I've been told is poor flow from the
exhaust port (small and poorly shaped). A couple of websites state that a
4-2-1 header can be tuned to give more power than the 4-1 header over the
entire rpm range.....?
http://www.burnsstainless.com/TechArticles/Theory/theory.html
http://www.importtuner.com/tech/0310it_serheaders/ (different split)
http://performanceweldingheaders.com/triy.htm
http://performanceweldingheaders.com/headertech.htm
http://www.popularhotrodding.com/tech/0310phr_burns/
http://www.thorleyheaders.com/tech_basics_triy.html
Randy Carter has reported a significant torque increase (whole rpm range, but
more in the 4-6000 range) using a merge collector with a 4-1 header.
The Burns site lists a book on exhaust theory which I am going to try to
locate.
In the meantime, is anyone using a 4-2-1 header? Know of anyone that makes one
for the roadster?
Got a counterpoint? I am all ears.....
Daryl
'66 1600
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