Quote:
Originally Posted by dannichols1474
rwest,
Check out Banish's book, specifically Chp 7 Ignition. At no load / light load the throttle valve(s) is(are) mostly closed so the cylinders are only partially filling with fresh air / fuel charge that is being diluted with exhaust gas which decreases the air / fuel burn rate. The slower burn rate requires more timing advance to ensure peak cylinder pressure occurs just after top dead center.
For my car, the OEM timing spec of 35 +/- 3 degrees at 6000 rpm is with vacuum disconnected. The 47 degrees of advance in the Ignition table represents 37 degrees of advance to account for peak engine speed plus 10 degrees of additional advance to take into account dilution effects of light load under cruise conditions. As load increases with increasing % TPS, the dilution effects go away, the burn rate increases so the additional 10 degrees of timing advance is not required and total timing goes back to just the amount needed relative to engine speed.
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Dan,
Thanks, great explanation. I just ordered the book as well.
Rutager