A couple dyno tuning notes Sept, 2002

What I like to do now (simplified, assuming no issues jump up.) :

1. Do a physical check over, you know your car, but you wouldn't believe some people don't check their oil or coolant before doing 5-10 WOT runs on the dyno.
2. Check the Idle fuel in open loop, how is the quality, more rpm or spark needed for bigger cam?
3. Check the cruising, how is the fueling in open loop, how is the throttle response at 60 -70 mph? Depending on gears, heads, and cam the car may require more timing down low to make up for the slow burn during lower cylinder pressure (pressure leak out during overlap, late intake valve closing, etc.)
4. Check out the idle trimming in closed loop, are they within correction range, or is the fuel trimming at the min/max? Make corrections in the idle injector offsets. things like rpm change can shift airflow in the LT1 plenum, so tune this only after the rpm and spark are happy.
5. Check the fuel trimming at cruise, make sure injector settings are okay, make change to injector constant, off idle injector offset allow you to trim if there is a variation between the cylinders. Again, cruise at 60-70 and adjust timing if necessary.
6. If everything seems okay there, time to WOT tune. make at least two runs without changing anything to make sure you have a good baseline.
7. If an detonation appears, verify sensor by lowering timing, if knock disappears it's real, otherwise it's false, replace sensor- or ignore the knock sensor (avoid if possible)
8. Make sure the Air:fuel is 12.5- 13:1 (NA) throughout the power band, lean mixtures promote detonation, so get the fueling right before adjusting timing.
9. Once the air:fuel is right and there is no knock appearing, vary the timing, try more timing (like 2 degrees) and less timing, see which way the engine likes to go, again maintain AFR 12.5:1 - 13:1 for NA cars. Watch the fuel pressure as well, dropping fuel pressure will make repeatability very tough.
10. At this point many problems may have shown their face, ignition problems causing quick nasty dips in the dyno graph, valve float causing steady drops in power after the torque peak (or before perhaps.) Make sure to fix these problems before continuing to tune, otherwise the tune will be off.

Once the timing is optimized, vary the AFR a point, if the car makes more power running richer, than let it run richer- if leaner, then let it run leaner to a point- generally 13:1 is the leanest you want to go, an knock will tend to show it's face by then.

Hope this helps, -Christian