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burnin oil · 02-09-2021, 09:18 PM

Just set the timing to high idle and be done with it. Disconnect the vac advance. Rev the motor until it doesn't advance anymore then set to 36 degrees while holding the rpms up. Lock the distributor back down. This will get you through the engine break in. You can rehook the vac advance after recording the new idle speed advance.

Setting timing to factory spec will not work on a non factory distributor. You have no way to know what wieghts are in there other than doing the timing the way I said and subtracting the new base timing from the 36 degrees. The speed of the curve is also unknown. I have never owned a dialback timing light that was overly accurate. As a side note some of the factory HEIs had around 40 degrees of advance from the factory on the later emmissions motors with base timing set to 0 degrees. These are not desirable but to prove my point on timing.

Every motor is different but SBC tend to like 36 degrees of overall mechanical advance ( base + mechanical from wiwghts) and around 20 degrees of vac advance for a total of around 48-52 degrees of total timing on a stockist motor. High performance tend to want the same mechanical advance with more base timing but less vac advance. Stock motors want the tighter heavy advance springs and lighter performance cars will take the lighter springs for the wieghts. In other words you want a slow advance curve.

Lastly you just have to try vac advance both ways. Most motors like full advance but some like ported.

Good luck.

02-09-2021, 09:18 PM	#19
burnin oil Registered User Join Date: Jan 2013 Location: Eastern TN Posts: 1,921	Re: Timing & Gas Milage Just set the timing to high idle and be done with it. Disconnect the vac advance. Rev the motor until it doesn't advance anymore then set to 36 degrees while holding the rpms up. Lock the distributor back down. This will get you through the engine break in. You can rehook the vac advance after recording the new idle speed advance. Setting timing to factory spec will not work on a non factory distributor. You have no way to know what wieghts are in there other than doing the timing the way I said and subtracting the new base timing from the 36 degrees. The speed of the curve is also unknown. I have never owned a dialback timing light that was overly accurate. As a side note some of the factory HEIs had around 40 degrees of advance from the factory on the later emmissions motors with base timing set to 0 degrees. These are not desirable but to prove my point on timing. Every motor is different but SBC tend to like 36 degrees of overall mechanical advance ( base + mechanical from wiwghts) and around 20 degrees of vac advance for a total of around 48-52 degrees of total timing on a stockist motor. High performance tend to want the same mechanical advance with more base timing but less vac advance. Stock motors want the tighter heavy advance springs and lighter performance cars will take the lighter springs for the wieghts. In other words you want a slow advance curve. Lastly you just have to try vac advance both ways. Most motors like full advance but some like ported. Good luck.