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Old 07-03-2011, 05:30 PM
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New guy vac question!

Hey, im new to the hot rodding world but i finally got my truck running its 62' GMC. Rebuild 283 punched to 292. Comp 268H cam, flat top pistions, fulie heads, edelbrock performer intake and an HEI dist from mallory. On top is an Edelbrock 600. New valves, seats, guides, rings bearings ect.


The question i have is, at a 650 rpm idle warm, it pulls about 7" of vac. At part throttle cruse it pulls about 15-13". Is this normal? I have the timing set to about 34 deg total because thats where it pulled the most idle vac.
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Old 07-03-2011, 05:36 PM
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What is the base timing spec? Is vacuum advance in use?
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Old 07-03-2011, 05:37 PM
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10deg base and yes the vac advance is hooked up
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Old 07-03-2011, 06:17 PM
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You'll need more initial. That's a big cam for that amount of cubes. The increase in vac when the vac advance is adding timing at part throttle tells you this.
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Old 07-03-2011, 06:18 PM
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What`s it hooked up to? a manifold full time source that pulls idle all the time including idle or a ported source which only pulls it off idle? Try this:
Set the base timing to 12 degrees before top dead center with the vacuum advance disconnected and plugged. Lock the distributor, reconnect vac advance to a full time manifold vacuum source, recheck timing, it should be 20 - 24 degrees before top dead center. Next lower the idle speed back down to 650. Test drive.
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Old 07-10-2011, 01:54 PM
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Quote:
Originally Posted by DoubleVision
What`s it hooked up to? a manifold full time source that pulls idle all the time including idle or a ported source which only pulls it off idle? Try this:
Set the base timing to 12 degrees before top dead center with the vacuum advance disconnected and plugged. Lock the distributor, reconnect vac advance to a full time manifold vacuum source, recheck timing, it should be 20 - 24 degrees before top dead center. Next lower the idle speed back down to 650. Test drive.

I tried exactly this, it drove well. nothing much has changed except it seems a bit snappyer off idle. but still 6-7" of vac. at idle
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Old 07-10-2011, 10:46 PM
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You need to recurve the distributor to allow 20-24deg base timing at idle.

Search my posts on the subject. Get a 10" high stall converter and 4.10's for that truck so the lil cammed up 283 can perform.


Last edited by F-BIRD'88; 07-10-2011 at 11:06 PM.
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