Timing
So I am looking for some experienced thoughts a suggestions on initial timing and total timing. Wanting to set up timing curve. Here it is 383 stroked to 496.
383 .060 over (4.310 bore). 4.250 stroke. Trick flow max wedge 270 heads 70cc. 1.5 harland sharp rockers. Cam is custom grind. Cam lift is int.440 duration282. Exh.429 duration 286.
Valve lift int .660 duration 322
Exh .643 326 duration.
Compression is 14:1. Looking for a good starting point for initial timing and total timing @some where 2800 rpm
It's been my long held understanding that to find initial timing for a specific combination, you simply slowly advance the timing at idle until the idle speed no longer increases (max vacuum).
In other words, start with your initial somewhere around 10 to 15 initial, warm the car, increase the timing slowly while turn down the idle if it goes above your normal idle speed, and keep advancing the initial until the idle speed no longer increases. Then back the timing off to get the initial timing right at the very point that advancing it any more no longer increases the idle. Adjust your idle A/F on the carb to 3/4 of a turn above lean mis-fire.
Once the initial is set, you can adjust the mechanical advance so the total timing does not exceed 34 to 36 total. Track or dyno testing will give you your final total timing.
I ended up locking out my MSD Pro-billet locked out at 34 total. It didn't need a start retard even when hot, but I only have 200 psi cranking compression.
I've since gone with the Progression Ignition programmable distributor specifically for the programmable vacuum advance feature. My initial and total mechanical advance are pretty much set-up at 35 from idle up with the vacuum advance bring it up to 42 at cruise & light throttle. It must be hooked to manifold vacuum, so the timing falls back when the throttle blades are opened.
The nice thing about this set-up is that it's programmable in real time and you get easy to real real time feedback while tuning.
