{"text_format":"3","workbook":"xls","n_sheets":3,"sheets":["Sheet1","Sheet2","Sheet3"],"read":"whole","date_system":"1900","formulas":"cached_only"}

{"sheet":"Sheet1","index":0,"n_rows":43,"n_cols":9,"rows_kept":43,"flags":["formulas_cached_only"]}
["Header Formulas from book “ Performance Tuning in Theory and Practice” by Graham Bell"]
[]
[]
[null,"HPL(Header Pipe length inches) = ((850*(360 -EVO))/RPM ) – 3",{"$nulls":5},"EVO = Exhaust Valve Opening"]
[null,"HPD(Header Pipe Diameter inches) = ((SCID * 16.38)/((HPL +3)*25)))*2.1",{"$nulls":5},"SCID = Cubic Inch displacement of a single cylinder"]
[null,"Piston Engine 4 stroke"]
["RPM","EVO (BBDC)","HPL Inches","HPD Dia Inches","SCID cubic inches",null,"Area","Volume in^3"]
[7000,73,31.85,{"v":1.579248206599713,"d":"1.5792"},40,null,1.9588025743947297,62.387861994472146]
[6500,73,34.53076923076923,{"v":1.4664447632711621,"d":"1.4664"},40,null,1.6889675258811698,58.321347874465935]
[6000,73,37.65833333333333,{"v":1.3536413199426112,"d":"1.3536"},40,null,1.4391202587389849,54.1948704103456]
[null,null,"  "]
[null,"Adjusted for Rotary Engine",{"$nulls":6}," "]
[null,"HPL(Header Pipe length inches) = ((850*(360 -EVO))/RPM *2) – 3",{"$nulls":4},"Multipled rpm by 2 as the rotary provides 2 exhaust events per port per 720 deg cycle vs 1 per port for the piston engine"]
[{"$nulls":6},"Book Recommended area (sq inc) for rotary exhausts"]
["RPM","EVO (BBDC)","HPL Inches","HPD Dia Inches","SCID cubic inches",null,"Street port","Middle ","PP Bridge Port"]
[7000,73,14.425,{"v":1.7841241161527712,"d":"1.7841"},40,null,2.25,2.5,3]
[6500,73,15.765384615384615,{"v":1.7841241161527712,"d":"1.7841"},40,null,2.25,2.5,3]
[6000,73,17.329166666666666,{"v":1.7841241161527712,"d":"1.7841"},40,null,2.25,2.5,3]
[]
[null," "]
[null,"Since the rotary puts out 2 pulses per exhaust port per 720 cycle and the piston engine only 1 pulse, that means we can divide the tube length in half"]
[null,"and get the same scavenging  of one pulse returned for each exhaust port opening per 720 cycle."]
[null,"So I adjusted the tube length HPL equation to compensate for the 2 pulses by multiplying rpm value by 2 as we get twice as many pulse from the rotary at every rpm."]
[null,"These calculated lengths compare favoriably to values for the PP in the book(page 58) I recommended-  which gives exhaust tube lengths for the PP of 10 – 18”.  "]
[null,"These calculations fault within those limits."]
[]
[null,"The adjustment to the diameter of the tube is less credible {:>), but here is my logic.  Since we still have only 1 exhaust pulse in the tube (due to it being ½ the length of the piston tube)"]
[null,"that would seem to indicate that the diameter of this shorter rotary tube does NOT really seem to need adjustment from the piston engine equation. However,  I have read"]
[null," that the recommended rotary exhausts diameters range from 1.7” to 2.00” depending on porting."]
[]
[null,"Since the PP in a racing configuration would be winding considerably higher rpm than you will be running – it would seem to sway the diameter selection (in your case)"]
[null,"toward the lower end of the PP exhaust diameter range  - or approx 1.8” dia (Mark, I think you indicated you would like to use that diameter due to its avaliablity)"]
[]
[null,"Also given the one chart I sent you which shows how adversely the PP is affected by exhaust gas pressure – another reason perhaps to go with the 1.8” dia rather than a smaller"]
[null,"size."]
[]
[null,"In any case, what I did was to take the exhaust area recommended in the book and calculated the diameter based on that rather than the forumla for the piston engine."]
[null,"The exhaust tube areas considered were 2.25, 2.5 and 3.0.  2.5 was choose as being in the middle and more likely to be less extreme than either end"]
[null,"low end = street port , high end = monster bridge port/PP"]
[]
[null,"So that's how I see it at this point."]
[]
[null,"Ed"]

{"sheet":"Sheet2","index":1,"n_rows":0,"n_cols":0,"rows_kept":0,"flags":["formulas_cached_only"]}

{"sheet":"Sheet3","index":2,"n_rows":0,"n_cols":0,"rows_kept":0,"flags":["formulas_cached_only"]}