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Evo Heads

Mfgr. Flow Ratings

All numbers below were pulled from the various manufacturer's specifications and are therefore NOT directly comparable, because of the variations in testing methods. All were normalized to 10 inches of water by Jon via his fancy engine simulation software. The Fast Company numbers were provided by Bob Schleiger, who notes "These numbers are at 10 inches and were done with my S&S intake attached to the intake port."




H-D stock

  intake:          94 cfm   @ .500" 

  exhaust:         99 cfm



Branch

  intake:         128 cfm   @ .500"

  exhaust:        110 cfm



B. C. Gerolamy

  intake:         139 cfm   @ .500"

  exhaust:        120 cfm



Edelbrock

  intake:         147 cfm   @ .600"

  exhaust:        120 cfm



Fast Company

  intake:         148.5 cfm @ .500"

  exhaust:         99.4 cfm 



  intake:         152.5 cfm @ .600"

  exhaust:        107.6 cfm 



RevTech

  intake:         145 cfm   @ .550"

  exhaust:        107 cfm 



 S&S

                  158 cfm   @ .600"



S.T.D.

                  145 cfm   @ .600"



"Remember, this still is not apples to apples. To quote D. William Denish, "Valve size, valve lift and anything attached to the port during the test, such as an intake manifold, carburetor or radius entry flange, will affect results." -- Jon Boulle
" S&S uses 2" intakes and oversize exhaust valves in their heads, unlike all the others. That, IMO is an advantage that is integral to their design, as is their piston shape." -- Christopher deHahn

Optimal Flow Rates

"I was going through my HeadQuarters catalog and found this chart for flow rates that are the optimal rates for different engines at different rpms. HQ says that the too much flow is as bad as too little and suggests that you stick pretty close to these numbers."

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

              ENGINE SIZE (cubic inches)



            82       89       97      106

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

   RPM      FLOW (cubic feet per minute)

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

   5700    121      131      144      157

   5800    123      134      146      160

   5900    126      137      149      162

   6000    128      139      151      165

   6100    130      141      154      168

   6200    132      143      156      171

   6300    134      146      159      174

   6400    136      148      161      176

   6500    138      150      164      179

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

-- Jon Boulle