OK, ive been working on a custom header project for a few months now. mostly reading, a little math, some measuring and lots of welding practice. I dont have time today to cover everything ive learned to date, but heres' what im currently thinking about:
- 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...
- 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...