LSA Question
Because they're calculating all of the valve events. LSA itself won't change IVC, ICL does.
Wellll, LSA and the advance or retard of any given cam WILL affect IVC. Grind another cam with otherwise identical specs but a different LSA and the IVC will change by 1/2 the LSA change. If a person is stuck on attaining a particular IVC point the cam advance or retard can be adjusted.
Dan, I know many are talking about valve events and particularly IVC. IMHO you would be best off studying David Vizard's Powertec 10 videos on camshaft selection and/or get a copy of his How to Build Horsepower book which also mentions his cam selection method. For a race engine this is a good starting point with other LSA's tested on a dyno. For a snappy and strong running street engine that wojld be overkill. Dyno time can be used to dial in cam advance or retard but is again a little over the top for a street engine. If you so desire a dyno test, use the time for proper breakin and tuning the ignition curve and carb or EFI.
I know those statements will ruffle crap out of the hardcore crowd on here, but you are learning and need to get the right cam now. That is what DV's 128 forula will give for LSA. After that you can chose duration looking to port flow. IMHO and Reic Weingartner's, get as much lift as the heads and springs will allow. For a street engine look to 0.500" to 0.550" lift. Street engines work well with about 4° cam advance and most cams will have that taken into account during the grinding process.
Before installing the heads, dial the cam to ensure it is correct according to the cam card. Install light checking springs on #1 cylnder.Then drop the head on without the gasket and just snug a few bolts to hold the head in place. With modelling clay in strips accross the valve reliefs adjust the valves. Now you can rotate the engine two revolutions. The head can nnow be removed to measure valve to piston clearance. When a gasket is installed for final assembly valve to piston clearance will be increased by the gasket thickness when compressed which is not an issue.
Remember the KISS principal and put the noise behind you. When selecting a cam grinder, talk to a few. Keep the 128 formula indicated LSA but probably not wise to go tighter than 108° or 106°. Also remember that as you increase duration you will get more overlap which will cause a rougher idle. This is what Comp does with their Thumper cam line. If you want the long duration cam you will probably need to increase LSA a degree or two and accept the rougher idle. Have fun with building a good engine but do not fuss over at what timing point your IVC is at.
If your head is hurting by all this email DV and he can spec a cam for your build and desired driving for a small fee. You can rest assured you will get a strong running engine that way.
