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First however, it might be worth testing to see if it is worth the effort. I am thinking we should test the low-end opportunity from more advance and the on boost opportunity to find our truly what our timing goals should be.
Testing low end timing advance.
This can be done as simply as resetting idle timing advance from the stock +1 (1 deg ATDC) with a timing light and going out and doing some acceleration runs up to 2500rpm. Do not go into boost much as you may not have enough boost retard protection. I suspect we could bump timing to about -6 to 9 deg at idle and feel the difference.
I would like to suggest that we also test eliminating the Vac-Retard function that comes from the fitting on the can at the distributor and closest to / facing it. Some of my reading indicated that vac-ret was added to cars to make them run hotter at idle for emmissions. When this is done idle will increase about 300rpm because timing is set to a more ideal level. If we try this we would just re-adjust the Air Bypass screw to reset idle. Timing will jump to about -8 deg at idle from this alone. Try adjusting for more advance and idle should increase further. Again if the idle increases is an indication that timing is at a more ideal point for the amount of load and AFR at that time. However, under load we can not take as much advance as when not under load. If we go to far the car will balk and tell us. Most likely we will get to the end of the adjustment range available at the distributor before we reach the best advance for acceleration. I suspect about -15 is going to be a good place to be.
Of course a better test would be to find a dyno and a good tuner to supervise and do runs from 1000rpm to 2500 or a load type dyno so load can be set at say 1500rpm and then advance timing from stock a little at a time and then backed off a little once the most power is found.
Testing Full Power timing under Boost Retard:
This is more involved and best requires a dyno and the supervision of a good tuner. I am thinking we would start by setting timing per factory procedure but at a lower setting to something like -22. I suspect we should use tune for max power at “Torque Peak” instead of HP Peak as or point of reference. My reasoning is at TQ peak we are most sensitive to detonation (running rich at TQ peak could be an advantage). I would verify AFR’s to be no leaner than 11.5 (or what ever your tolerance for risk and beliefs dictate).
From there after, try advancing timing some and retest until TQ is maxed and back off a little for safety. This should give us an indication of our ideal timing given our build and the type of fuel we are running.
We will probably not know our actual timing goal under load unless we sit on the timing light when on the dyno. We will have to back into it.
Until then I suspect we want to be at about -15 to -18 at full boost.
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