Timing curve for my big-cam 451?
At the most you need about 5° advance in the distributor and that's only for starting. Your blowing smoke up your own butt thinking you need vacuum advance. Iron heads consistantly need 38+ degrees of total timing.
I think
you're blowing smoke up my butt. :p
Remember, this is a street-driven car on pump gas, sometimes in hot weather. I would rather give up a little power than run the absolute max timing and risk knocking under full throttle at high rpm. That tends to be hard on ring lands and piston tops :eek:
My engine does not like to start hot with 28 deg initial (which it would be with your suggested 38, and 5 distributor degrees).
With my big cam and low cylinder pressure at low speeds, plus the lean cruise mixture and poor volumetric efficiency at part throttle, more than 38 degrees of timing is desirable. 50+ degrees is usual at cruise! The fuel economy will be better, the engine will run cooler, the plugs and oil will stay clean longer, etc. Why do you think every street car has a part-throttle advance, whether old-school vacuum can, or built into the EFI map?
I agree that up to 38 degrees can be run with the mildly ported iron heads. This winter I'm finally going to put my PRH-massaged aluminum heads on (293.5 cfm), which may change the required advance.
Anyway, your approach seems to be for a strip-only car that happens to be street-driven occasionally. All that engine needs to do is have the right timing at WOT, and start.
What I have here is a mostly street car that may be on the strip once in a while :)
Edit: 38 deg of timing is only going to be optimal at one setting - full throttle and above 2500-3000 rpm. It is wrong at all other conditions of load, throttle setting and rpm unless that timing requirement just happens to coincide with 38 degrees. Even my cam doesn't need that much at idle, and certainly not during a typical departure from a stoplight (not a clutch-sidestepping dragstrip launch). Lean mixtures burn slower...
