I don't know if it will help, but my 1977 copy of The Design and Tuning of
Competition Engines shows a picture of a four-two-one system with cylinders 1
and 4 joining and 2 and 3 joining and then those two meeting into the one. I
think that would make 1 and 3 on the same branch and 2 and 4 on the same
branch, figuring a 1,2,4,3 firing order. The book claims this is best for mid
range power with 4 into 1 being best for WOT and high speeds.
Page 206, figure 6-12 states:
"Unfortunately most "street" headers are designed largely for easy
installation and inexpensive manufacture and do not make use of tuning
principles that
would be beneficial in highway driving. Subdivided systems such as those
shown in Fig. 6-12 are normally best for improving mid-range power; the
four-into-one headers, commonly sold for inline "fours" and V8s, are effective
mainly at wide-open throttle and high speeds."
On page 309 of the book they give lengths from port to 1st junction as 18"
and 1st junction to 2nd junction as 24" but don't give a diameter. It does
state, "The pipe diameter is based one the dimensions of the valve
throughway."
It does give a formula for determining individual pipe lengths as
2
ASD
P= ---------------
2
1400 d
Where P= pipe length in feet
A=exnaust valve opening in degrees of crankshaft rotation
S= engine stroke in inches
D=engine bore in inches
d=exhast port diameter in inches
It also refers the reader to The Scientific Design of Exhaust & Intake
Systems for more detailed information.
Hope this helps...
Dave
59 BT7 project (yes, still)
Paradise, CA
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