- on a 4-2-1 header, as part of a whole exhaust system, at what point is the low pressure sonic wave from an exhaust charge reflected back up the pipe?

-is it when it reaches an area of +10x the cylinder volume?

-is it when it merges with it's paired primary?

-is it at the 2-1 collector?

-is it as a square wave (closed pipe), when it hit's the cat's catylist?

-is it at the very end of the tail pipe?

-somewhere else?

currently im trying to figure this out by means of comparing Smith's ideal length formula with actual measurements from the OEM manifold from a 98 typeSH.

according to Smith's "Scientific design of exhaust systems" (i know its old, if you have better reading let me know!) here are some optimal primary lengths for acoustic tuning, according to several estimated volocities of sound in exhaust gas:

estimated ideal length for open pipe primary according to Smith

--------------------------------------------------------------------------------

L = V*T/RPM

L = ideal length in inches

V = velocity of sound in exhaust gas, can range from 1100 - 1900 fps

T = 120' exh port open time in crankshaft degrees (is this correct for h22a4?)

RPM = disired torque peak RPM

-RPM----2k----3k----4k----5k----6k----7k----8k

1100fps-66----44----33----6.4---22----18.8--16.5

1300fps-78----52----39----31.2--26----22.8--19.5

1500fps-90----60----45----36----30----25.7--22.5

1700fps-102---68----51----40.8--34----29.1--25.5

1900fps-114---76----57----45.6--38----32----28.5

2050fps--------------------------41----35----30.75

H22 EGT = 1200-1500f

speed of sound at 1300f = 2050fps

*Smith used 1700fps for his work, and suggested interference pipes (which in a 4-2-1 means the paired primaries) not exceed 18" length (but i dont know where that # came from...?)

OEM exhaust manifold info

---------------------

primary (port to non-sequesncial merge)

length: 32cm (12.5")

dia: 3.8cm (1.5")

2ndary (1st merge to 2nd merge)

length: 51cm

dia: 4.5cm

pipe to cat

length: 44.5cm

dia: 4.8cm

exhaust port dimensions:

4.5x3.5cm oviod

12.85cm^2 area

tottal length (1port to cat): 127.5cm (50")

*lengths include 1cm flages, where appropreate

top, center flange bolt distances 9.5cm, 8.5cm, 9.5cm

flange bolt whole diameter: 8mm

2ndary down segment length:13cm

2ndary post curve to collector length: 38cm

2ndary collector to flex length:5cm

2ndary flex length: 20cm (8")

look at these NASTY transitions:

where is it? LETS TALK!!

ps- if anyone has the equivilant numbers for the mugen header id realy appreciate it, itll save me 4+hrs of camera matching and reverse engereing in 3dsm...