The Ford Barn - View Single Post - 292 y-block distributor puzzler

scicala · 09-21-2019, 02:24 PM

Even if you have the specs on how much vacuum to the distributor inner diaphragm, and how much spark advance that vacuum level represents, I don't think you will be able to check it with a timing light unless you have the engine on a dyno, or the car on a chassis dyno since all the specs are based on light to heavy loads on the engine and not racing the engine in neutral. I can tell you based on my Holley carb manual that the most vacuum you will see is about 4" hg. And that is at high RPM and basicly wide open throttle. At that point the vacuum signal is mostly from venturi vacuum (suction)and not manifold vacuum. Manifold vacuum at wide open throttle will be no more than 2" hg at high RPM.

Sal

09-21-2019, 02:24 PM	#38
scicala Senior Member Join Date: Jun 2010 Location: Detroit suburb, MI Posts: 3,706	Re: 292 y-block distributor puzzler Even if you have the specs on how much vacuum to the distributor inner diaphragm, and how much spark advance that vacuum level represents, I don't think you will be able to check it with a timing light unless you have the engine on a dyno, or the car on a chassis dyno since all the specs are based on light to heavy loads on the engine and not racing the engine in neutral. I can tell you based on my Holley carb manual that the most vacuum you will see is about 4" hg. And that is at high RPM and basicly wide open throttle. At that point the vacuum signal is mostly from venturi vacuum (suction)and not manifold vacuum. Manifold vacuum at wide open throttle will be no more than 2" hg at high RPM. Sal