This is a posting to your build diary so you have a record of our conversations & emails regarding cam selection/fitment.
The next step is to determine what actual "net valve displacement" (valve lift @ crank position) will fit. If your choice of cam grinder can not (or will not) provide you with "net valve displacement", the cam "lobe displacement" would be a more math intensive second choice. The formula for your little jewel is: cam lobe displacement * effective rocker ratio - valve lash = net valve displacement @ a certain crank position. Repeat for other crank positions as required, to calculate minimum valve to piston clearance for both valves.PROPOSED CHANGES TO CURRENT BUILD SPEC:
The minimum information required is: inlet lobe lift @ 10/12/14 degrees ATDC at the specified LCA for cyl's 1/4, and....
inlet lobe lift @ 10/12/14 degrees ATDC at the scattered LCA for cyl's 2/3, and....
ex. lobe lift @ 10/12/14 degrees BTDC at the specified LCA.
Some of the above can be calculated, IF, the cam mfg. shares info about whether it is a single pattern cam. If it is a dual or multi pattern cam, then all of the above is required to check fitment.
In valve depth/height: .205" net (After milling .065" from face of head to raise C/R)
Ex. valve depth/height: .195" net (See above)
Head gasket thk: .025" net (After milling .012" from block, changes piston height from -.004" to +.008" Actual gasket .033") DIMENSIONS FROM BUILD GEOMETRY:
Piston depth @10 degrees B/ATDC: -.022" (+.022" piston depth gained. Note that this is not the actual piston dimension.)
Piston depth @11 degrees B/ATDC: -.027"
Piston depth @12 degrees B/ATDC: -.032"
Piston depth @13 degrees B/ATDC: -.038"
Piston depth @14 degrees B/ATDC: -.044" (I can supply a piston movement chart, if required.)RESULTANT SPACE AVAILABLE FOR VALVE DISPLACEMENT:
Max In valve lift @ 10 ATDC: .202" @ .050" Valve to Piston clr. (can notch piston if req'd)
Max Ex valve lift @ 10BTDC: .172" @ .070" Valve to Piston clr. (can notch piston if req'd)ALSO REQUIRED FOR CALCULATION OF VALVE TO PISTON CLEARANCE:
Rocker Ratios: Int: 1.53/1 measured Ex: 1.52/1 measured (1.50/1 nominal Harlan Sharp roller rockers)
Valve Clearance: Int: .016"/.018" Ex: .018"/.020" INFORMATION PROVIDED BY CAM GRINDER FOR THE PROPOSED CAM:
Cam ground on 110 degree LCA's. 1/4 Inlet lobes & all exhaust lobes. 2/3 Inlet lobes 3 or 4 (?) degrees (cam/crank?) advanced.
1/4 cyl Inlet Cam lobe lift: Net valve lift: Resulting valve to piston clearance:
@ TDC: .10161655" .139" .091"
@ 10ATDC: .1353" .191" .061"
@ 12ATDC: .1420" .201 .061"
@ 14ATDC: .14879" .212" .062"
These all exceed the .050" minimum dimension for inlet valve to piston clearance, so that's good. With a calculated valve displacement increase of .010" per 2 crank degrees the cam could be advanced to 108 degrees and still have .051" V/P clr.Presuming
that this is a single pattern cam, then the exhaust numbers would be reversed from the intake, thus:
All Exhaust Cam lobe lift: Net valve lift: Resulting valve to piston clearance:
@ TDC: .10161655" .136" .084"
@ 10BTDC: .1353" .188" .054"
@ 12BTDC: .1420" .198" .054"
@ 14BTDC: .14879" .208" .056"This is a bit on the tight side for me, BUT, advancing the cam 2 degrees (as above), would net an additional .010" clearance for a minimum of .064". Also, the head milling could be held @ .060" rather than the .065" I suggested. This would add .005" clr to both intake & exhaust. The new net Ex. clr of .069" is a number I could live with, IF, valve train motion is well controlled. (as in timing chain tenshioner.....) The resulting additional .005" inlet V/P clr also would allow the cam to be advanced another .005" of lift = 1 crank degree, which MIGHT be useful. That 1 degree would give .051" inlet net & .074" exhaust net.
Right about now is what I mean when I say you'll have to slice the cheese mighty thin.... (have I mentioned that "It's complicated"?) NOW THE BAD NEWS:
The clearance for the "Scattered" 2/3 inlet lobes is going to be less, a lot less perhaps. If the lobe centers are 3 (crank) degrees advanced, then the valve to piston clearance will be .015" less than the 1/4 inlets. If the lobe centers are 6 (crank) degrees advanced, (as in the cam you had profiled), then the valve to piston clearance will be .030" less than the 1/4 inlets. While not an acceptable number, it is close enough for some compromise for fitment. Notch the pistons for V/P clearance, OR retard the cam back to ~109 degrees intake, OR, widen the LCA to 111/112, OR, std, unscattered cam, OR, an alternate cam with less flank lift @ 10/12 BTDC/ATDC, etc.What should be obvious is that you are near to the point of "Maximum Cram". WHAT I THINK YOU NEED TO DO NOW:
1 You need to have a dialog with your cam grinder(s) to CONFIRM all the figures being used to calculate these numbers, OR, research
alternate cam choices.
2 You need to make some hard choices about suggested changes to the build. (I suggest maximum C/R be preserved.)
3 You need to take the c-clamp off your head & grab a cold suds, and relax a little while contemplating the choices.
4 Call/email me if you want to converse off line.