Looking for more pep off the line
By my calculations I should go with a 106 or 107 LSA cam, depending on the size of my valves. 367/8=45.875/2.02=22.71x.91=20.6-128=107.3
My CR is 9.6:1 currently, but will go up if I mill the heads a bit.
Another thought DV states is that if you are going to err on LSA, go a degree tighter. When doing the calculation do not forget to multiply the valve diameter by .91. The valve seat is generally in a little from the outside diameter. So a 2.02 valve × .91= 1.838. 45.875/1.838 = 24.959. Rounding it to 25 is OK. 128 - 25 = 103°. Doubtful you will get anyone to grind a cam that tight. You may be able to get 105° but 106° may be easier.
In Billy Godbold's High-Performance Cams and Valvetrains book, he speaks in selecting EVO and IVC points and then IVO and EVC points. He also goes into these as they are related to NA, supercharged, turbocharged and nitrous.
EVO starts cylinder blowdown and the pressure wave tuning.
IVC is when piston compression starts.
Ivo and EVC are the overlap figures.
A different method of going about selecting the timing events and to use this you better have intimate knowledge of camshaft design.
DV essentially simplifies this by determining the LSA. You then can use acceptable overlap to determine duration. More duration equals more overlap and more misfires delivering the loppy idle, but more power at higher RPM.
When you talk to the tech at comp he will want to convince you toward the 110° to protect themselves if the idle is too choppy. That could be once you get to the 280° to 290° cams, but the XE268H is not much more than an "RV" cam. At 110° they are fairly docile.
I installed an Engle
[email protected], 210@ .050 cam.in a 351W. This cam was ground on a 109° LSA and has .472 lift. It is a hyd flat tappet cam. Very docile with smooth idle but a bit more torque and fuel economy. That same cam will go in my 0.030 over 289 with 1.9/1.55 LS valves. The LSA by formula should be 107°, but I will be shooting for 11 to 11.5:1 compression. Intake rockers will be Scorpion 1.72:1, so the intakes will be quick off the seat. Best LSA would likely be 108° but considering I have the cam I may as well use it.
That 351W got rebuilt even though it ran great. It has the 1.78 intake valves and the 268H cam. The truck has not been completed yet, but I think my 289 may be a stronger runner.
