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tune your exhaust
anybody like a post of the one shown below send the information and i will try to post the results. supposed to be pretty correct within inches proven on dyno. in order of importance: primary size, collector length & size, primary length. from what i understand equal length headers haven't shown the benefit worth the investment. might just do this for a few engines and everybody could use the info.
bore stroke rod length peak hp rpm comp ratio int/ex valve dia. valve stem dia. int/ex valve lift int/ex valve lift int/ex dur. at .050 int degreed centerline lobe center angle centerline length of ex port from valve face to manifold mounting surf. some of the above can be estimated and similiar engines will not skew the results much. the below is for a 3.80 stroke 4.125 bore making peakhp at 6600rpm --- Single Primary Pipe Specs --- for 406.268 CID from 4600 to 7100 RPM Diameter= 1.752 to 1.877 Length= 27.4 to 30.3 inches long --- 2-Step Primary Pipe Specs --- 1st Dia. inches= 1.752 Length= 13.7 to 15.1 2nd Dia. inches= 1.877 Length= 13.7 to 15.1 --- 3-Step Primary Pipe Specs --- 1st Dia. inches= 1.752 Length= 13.7 to 15.1 2nd Dia. inches= 1.877 Length= 6.9 to 7.6 3rd Dia. inches= 2.002 Length= 6.9 to 7.6 --- Header Collector Specs (Conventional Straight Tube) --- Diameter= 3.215 to 3.465 Tuned Lengths= 16.2 best and also 8.1 or 32.5 --- Header Collector Specs (Megaphone or Diffuser Cone Shape) --- Diameter= 2.715 taper to 3.715 Megaphone/Diffuser Length= 16.2 inches Best HP/TQ Tuned Collector Lengths= 16.2 , 32.5 , 65.0 , 129.9 inches long Worst HP/TQ Loss Collector Lengths= 24.4 , 48.7 , 97.4 , 194.9 inches long Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness ---- Primary Pipe's Harmonics ---- 1st Harmonic = 121.8 inches long ... typically never used 2nd Harmonic = 46.0 inches long ... longest recommended 3rd Harmonic = 27.4 inches long ... highly recommended , best Torque Curve 4th Harmonic = 19.1 inches long ... shortest recommended 5th Harmonic = 14.3 inches long ... typically never used 6th Harmonic = 11.2 inches long ... typically never used 7th Harmonic = 9.0 inches long ... typically never used 8th Harmonic = 7.4 inches long ... typically never used ---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ---- 1st Harmonic = 129.9 inches long ... longest with Mufflers and TailPipes 2nd Harmonic = 65.0 inches long ... longest recommended with Mufflers 3rd Harmonic = 32.5 inches long ... more bottom-end Torque 4th Harmonic = 16.2 inches long ... highly recommended , best Torque Curve 5th Harmonic = 8.1 inches long ... reduced Torque , more top-end HP sometimes 6th Harmonic = 4.1 inches long ... reduced Torque , not recommended |
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