My recently acquired '72 Duster has a sticker for timing that says set initial at TDC. My 1980 D-150 truck timing sticker says set initial to 12* BTDC. How can that be? The '72 is a points ignition and the '80 is an electronic ignition. That can't be the reason can it?

bwhitejr

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

No, it's because the factory built very different advance curves into the two distributors, and was employing different emission control strategies in 1980 than they had been in 1972.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

They actually employed a similar timing curve through the 1973-1974 years even with the EGR installed (initial at TDC...15R governor), then about 1975 with the advent of adding a cat. conv. they changed to the "more initial" timing curve(10-12BTDC, 9R governor...except some canadian and california cars).


-D.Idiot

So, the distributor uses the same weights for the mechanical advance curve, but uses a different governor and initial timing, right?

bwhitejr

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Probably different springs, different governor, different vacuum advance pod.

For what its worth, the factory timing on my 86 Dodge van with lean burn and spark control was 16 degrees BTDC.

What is so bad about the 15r governor that the 70's cars came with. The distributor on my duster has one and everybody says that I should change it. Does it give a bad advance curve or something?

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

This is close, the weights have been the same since the 60's. THe springs are slightly different between the curves but most will come in a few hundred rpm of each other as a set. The vacc. pods changed back and forth as to when they came on (depending on load, car size, mileage maker) and year (by the mid-70's they had a nice 11x vacc. pod to give that nice 52 degrees of highway mileage and mild pinging advance).


Slants really like a fair amount of initial in their timing curve. As a generality some mechanics would agree that lighting the fire a bit early in the combustion chamber on a low compression mill helps make pressure a little bit earlier, making a bit more power, better response...to a point ( don't go out and twist the dist. over to 20BTDC and expect it to whop a hemi...). The early 70's timing curve was about averaging pollution control with mileage, as power dropped off in the 70's with more pollution controls and the need for more complete combustion, better mileage, someone decided to dial some more initial into the slant's curve. THe 1976 curve still comes out about the same as the 1974 curve, but the governor doesn't have to ramp up that 1" slot to get to the much wanted 30 degrees mech adv... it only has to grab 18 more degrees on the governor. You might want to find one of these distributors, plug it in, and see how it affects your car (I know my '74 liked things much better).

If you do convert to the later curve, you will have to 'dial it in' a bit since octane isn't as good as it used to be (here in Oregon the 'ping factor' varies from station to station).


-D.Idiot