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Old 04-18-2010, 08:15 PM
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vacuum advance on my engine

Yes I know to research for the thousand threads on vacuum advances but could not find any referring to my engine. I've got the GM 260hp crate engine in my 72 Chevy c/10 pickup weighing 4500 ibs. so small performance and small camshaft. I put on an Edelbrock Performer intake an Msd Streetfire hei distributor with a Holley Street Avenger 570 carb. pickup runs good in both timed and full port but full port is a little better. However, I have initial timing in timed port at 10 btdc at 650 rpm in gear pulling 16* of vacuum at idle. When I hook up to th full vacuum port the rpm jumped to about a 1,000 meaning my advance works and certainly jumped up in timing, but it feels like maybe its going to diesel when I shut it down any thoughts should I change back to timed port or lower the idle speed, timing, or both?

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Old 04-18-2010, 08:18 PM
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Quote:
Originally Posted by kpcrossfire6
Yes I know to research for the thousand threads on vacuum advances but could not find any referring to my engine. I've got the GM 260hp crate engine in my 72 Chevy c/10 pickup weighing 4500 ibs. so small performance and small camshaft. I put on an Edelbrock Performer intake an Msd Streetfire hei distributor with a Holley Street Avenger 570 carb. pickup runs good in both timed and full port but full port is a little better. However, I have initial timing in timed port at 10 btdc at 650 rpm in gear pulling 16* of vacuum at idle. When I hook up to th full vacuum port the rpm jumped to about a 1,000 meaning my advance works and certainly jumped up in timing, but it feels like maybe its going to diesel when I shut it down any thoughts should I change back to timed port or lower the idle speed, timing, or both?
Leave the initial alone, at least for now. Lower the idle speed by using the curb idle screw.

All there is to it!
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Old 04-18-2010, 08:52 PM
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I've got the same crate motor in my Chevelle, and with the vacuum advance pulling full manifold vacuum with about 12-14 degrees initial advance it never diesels when I shut it off.
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Old 04-23-2010, 10:57 PM
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With my initial timing 10* BTDC. With the vacuum advance hooked up to full manifold idling at 600 rpm in gear, what should my advance be at or close to in idle with my advance hooked up? I have an adjustable vacuum advance and timing tape on my balancer. I also realize its hard to determine what every engine wants and demands but could someone give me a guideline or what it would be close to in idle with advance hooked up.
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Old 04-23-2010, 11:17 PM
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I would advance it to 12 degrees btdc with vac advance disconnected and plugged. Reconnect vac advance, the advance at idle should be 20 - 24 degrees. It detonation is detected, retard it 2 degrees at a time until it`s gone and it`s set.
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Old 04-24-2010, 12:33 PM
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Quote:
Originally Posted by kpcrossfire6
With my initial timing 10* BTDC. With the vacuum advance hooked up to full manifold idling at 600 rpm in gear, what should my advance be at or close to in idle with my advance hooked up? I have an adjustable vacuum advance and timing tape on my balancer. I also realize its hard to determine what every engine wants and demands but could someone give me a guideline or what it would be close to in idle with advance hooked up.
The vacuum can will add somewhere around 12-16 of additional vacuum at idle. This will depend on the exact specs of the vacuum advance can that you're using- OEM cans varied by application.

If you find that the can gives you more advance than you want (10-12 "in the can" is usually optimum for most performance set-ups), use a limiter (or make one).

The Crane part: VACUUM ADVANCE LIMITER PLATE- Crane #99619-1: 99619-1 INSTRUCTIONS.

AFA the adjustable vacuum advance can, the setting that you change by rotating the adjuster sets the vacuum point where advance is added or dropped. 99600-1 INSTRUCTIONS.
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