have 69 roadrunner 440/727....just got it together the other night and got it rumbling....my first mopar build. I'm excited to get into the building of motors and away from my normal profession....anyway....to my question....I know the mechanics behind setting the timing, but in changing from a stock cam to a different cam to I'm sure that I make timing changes, but what changes I'm unsure of. Retarding or Advancing...a mechanic I know says that I can use the cam card to get close....is this true? My hydraulic cam is gross lift 507/507 duration @.05 235/235 lsa/icl 108/104. thanks guys for helping a learning mopar guy and forgvie the long question....just excited about this car and new hobbies. you just can't beat the sound of a big block and looking over at the red light at an import.
There are many variables that could effect your initial advance setting, but generally you can get close by knowing the camshaft duration at .050". So the mechanic was correct by saying to use the cam card.I will not be taking into consideration the vacuum advance you would be using in light load/cruise conditions. This will only be about initial advance and mechanical advance.You are generally safe using 36 degrees total advance (initial + mechanical) in a 440 IF you are using the proper octane fuel. The ratio of initial to mechanical will change depending upon duration at .050With 440 ci and <220 degrees at .050 use 10-12 degrees initial & 24-26 mech. 220-240 @ .050 use 12-16 20-24 mech 240-260 @ .050 use 16-20 16-20 mech 260+ @ .050 use 20+ 15 or less Once you have found the correct initial timing, add mechanical advance so you have a total of 36 degrees.As an example, on a recent 451 we built we used a cam with 276/280 @ .050 and found 28 degrees initial and 10 mechanical for a total of 38 degrees to work very well. A 383 with 218/224 liked 17 degrees initial and 20 mechanical for 37 total.Again, these are general suggestions to get you in the ballpark. Make sure you are using the correct fuel for your cylinderhead design, cam design and compression ratio. You will have to do your own tests and plug readings to get everything correct for each individual engine.