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Old 10-17-2006, 04:29 PM
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vac advance

i have been getting a lot of pinging with my 350 chev . had it timed 3 times. to day i unpluged vac line from carb and no more ping.whats up with that.

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Old 10-17-2006, 04:40 PM
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Engines ping when rhe timing is too far advanced, amongst other things. Your timing is too far advanced when the vacuum advance kicks in. You could leave it unhooked, but will lose power and economy. You can back the initial timing off...............Or you can run hightest gas.

Where is the vacuum advance hooked up to on the carb....I am guessing direct manifold vacuum.
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Old 10-17-2006, 06:05 PM
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it was hooked up to the carb.
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Old 10-17-2006, 06:36 PM
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Quote:
Originally Posted by big red 1
it was hooked up to the carb.
Yes, but where?

At the bottom of the carb is manifold vacuum......Part way up on the carb is ported vacuum which is 0 at idle, but increases when you rev it up....That is the one you want.
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Old 10-17-2006, 06:39 PM
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vac advance

Now here is a subject that usually generates lots of interesting responses.First off I will say that there are lots of people,enginer's and papers written by enginer's that will swear that vacuum advance is the only answer to proper operation of an automobiles distributor/ignition system.Yes,auto manufacturers used them in millions of cars,probably to help with emissions control.But,you do not necessarily need vacuum advance for proper operation of your car.I have not used it in my daily driven LS-6 big block powered Monte SS for a few years now,mostly because I was having problems similar to what you described.My friend Mark,a class A mechanic,talked me into unhooking it,and I was glad that I did.It has not affected driveability,gas mileage,or spark plug longeivity.All around performance has improved,no more pinging at part throttle,mine also used to have a slight stumble, but no more.So,before all the nay sayers chime in,look at it this way.If it works better,you probably dont need vacuum advance for your application.Dont let anyone elses opinions but your own be the judge!
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Old 10-17-2006, 08:23 PM
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it sounds like the vac advance unit has too much advance for your engine and fuel paqckage. depending on the type of distributor you have you can limit the advance from the vacuum can. we limit the advance from the vac can to 10 degrees, on a hei style distributor we use ac/delco unit # D1370a or on a points/msd distributor we make a bushing that goes on the vac advance pin where it goes into the distributor plate to limit the vac advance travel to 0.120" or 10 degrees. you can just disconnect the vac advance if you want but it can hurt the fuel mileage if the car is a daily driver


henry @ oles carb
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Old 10-18-2006, 05:18 PM
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Quote:
Originally Posted by olescarb
it sounds like the vac advance unit has too much advance for your engine and fuel paqckage. depending on the type of distributor you have you can limit the advance from the vacuum can. we limit the advance from the vac can to 10 degrees, on a hei style distributor we use ac/delco unit # D1370a or on a points/msd distributor we make a bushing that goes on the vac advance pin where it goes into the distributor plate to limit the vac advance travel to 0.120" or 10 degrees. you can just disconnect the vac advance if you want but it can hurt the fuel mileage if the car is a daily driver


henry @ oles carb
I agree. You did not state what your total mechanical timing was @ what rpm. I run 36* all in by 2600 rpm. Got the PROPER vacuum can to give me another 14* at 11" vacuum (idle vacuum is 13" - bigger than stock cam) and pipe it to the manifold vacuum port. The ported vacuum port came into being for the smog stuff.

So, at cruise, I have about 50* total advance - total mechanical + vacuum advance. The vehicle likes this!

Engine is 383 SBC 10.3 static CR 8.33 dynamic CR, 64CC TF aluminum heads, Speed Pro 12cc dish pistons on an Eagle rotating assembly, ZERO deck block, CC XE274 hydraulic cam, and a QJET.

Been running nicely, on 89 octane, since I built it.
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Old 10-18-2006, 07:29 PM
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im running a 350. with mild cam. elderbroc manafold and 650 carb.hei dist.now that i unplugged vac i have no more ping but its a Little bogey at first.cant i get a dist. with adjustable waits will that help
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Old 10-19-2006, 04:08 PM
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vac advance

MSD makes a real nice Pro Billet HEI replacement distributor # 8365.Built in rev limiter,3 sets of advance springs,3 different bushings to control centrifugal advance,matching coil,and it has a much better mechanism than a stock HEI.I bought one this year for my car and I am very happy with it.It also has a vacuum advance lock out and a real slick cover for the hole that the vac advance can sticks out of.It's a real good investment as far as I am concerned!
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