I asked this question when building my current motor
I got lots of great advice with lots of varying views
I learnt a lot about cam timing, but i'll admit not enough.
Not enough becasue like many i build an engine once every 10 years or so,i make changes rarely, got teenage kids and a house to maintain, work a 40 hour week so i'm never in a position to try try try again, comparisons back to back are not really that possible.
i need it to be an improvement over what i had.....so i have to make the best of it
Also until its in bits and you can measure, you are not fully availed of all the facts
i found it easier to take all the suggested cams
and run them along with the measurements i had taken or had got from the manaul
in this software
http://cochise.uia.net/pkelley2/dcrvb6.zip
it should run on old PCs xp win7 win 8 and will run, or run in, "compatibility mode" on win 10 and win 11 provided your windows allows you to install any softwre you like. not just stuff from the microsoft app store (usualy cheap lap tops and tablets are stuck with that)
it does everything for you, so you don't have to manully do the maths
discussed here
Dynamic CR
with your rod length, your stroke (rod ratio) your bore your combustion chamber CC and the deck height.... the bore of your gasket and its compressed thickness the cc of the valve relief in the piston etc.
you can plumb in the cam figures to check DCR, fill first tab, use answer from first tab in the second tab and repeat the process again in the 3rd tab
look for a cam that gives a DCR in the 8.8 to 9.1 range 9+ with good manifold and distrinbution closer to 8.8 with a crap one.
it aint a magic bullet but it gives you an idea of the cam needed to produce a motor with decent cylinder pressure, decent torque and that will run ok on the gas you intend to feed it without pinging.
the actual cam spec you come away with might be slightly off what you expect, becasue most talk in the realms of static CR and its dynamic CR that counts, but if you put in the cam figuers as specified and put the chosen cam in te motor straight up that motor will run nicely, provided that its a quality assembly, correct advance curve and decent tune
its very good if you don't want to buy anything more, have to work with what you have and just need to home in on a cam spec.
in the right hands you can use this as the centre of a build and adjust stroke rod ratio static CR etc but thats for the guys who do this every day or race rather than play at the track. But it works very well the other way as well. everything fixed (no more money to spend) apart from the cam n lifters....
its a tool to help with the math. A person builds a nice motor, not a computer program. but i sure found it a great help.
It might help in your quest.....
Dave
