Posted by Dave Horvath [24.131.120.209] on Monday, March 25, 2013 at 19:39:01 :
Getting ready to set the timing on the 1967 WM300 with the 318-3 poly out of a 1967 D500. MSD electronic ignition and high performance cam. Engine idles OK (period of high vaccum), but lacks power and backfires at high rpms and under load (periods of low vacuum).
Here is what the Dodge Trucks Service Manual for 1967 says:
318-1
Timing: 5 degrees BTDC
Advance-Vacuum (Distributor Degrees at Inches of Mecury)
Zero degrees @ 8" to 10"
5 to 8 degrees @ 13"
9 to 12 degrees @ 16"
318-3
Timing: 12.5 degrees BTDC
Advance-Vacuum (Distributor Degrees at Inches of Mecury)
Zero degrees @ 5" to 7.1"
4 to 7 degrees @ 9.2"
8.5 to 11.5 degrees @ 12"
Questions:
Why is the 318-3 timing so much more advanced than the 318-1? The compression ratio for the 318-3 is 7.5:1 vs 8.25:1 for the 318-1.
For the initial setting at idle (500rpms) with the vacuum advance disconnected, should the timing be set at 12.5 degrees BTC, or set at 12.5 plus the additonal 8.5 to 11.5 degrees at 12" (high vacuum) for a total of 21 to 24 degrees BTC? Seems like a lot of advance.
By the way, the 318-3 takes Champion F10 plugs (18mm) vs the Champion J14Y (14mm) plugs for the 318-1.
Thanks.
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