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I have an adjustable vacuum advance on my HEI and I'm not sure how to measure/read where it's set. How do I know where it's at? Initial timing is 16º and it's at 36º @ 2800 rpm.
 

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oh boy another can of worms opened up. do you have it hooked up to manifold or ported vacuum? take readings with the vac canister hooked up and not hooked up. There should have been a small allen wrench included with the distributor so you can adjust the canister. Give it 4 full turns in one direction see what it does. Then go from there.
 

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It's on the carb itself and yes I have the allen wrench!
 

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Start with the allen wrench adjusted fully clockwise. Hook up the hose and test-drive the vehicle in the city and on the highway while listening for audible spark knock under heavy load and part throttle. If spark knock occurs under part throttle conditions, a change in the vacuum advance curve is needed. This adjustment is made by inserting the 3/32" allen wrench into the vacuum advance unit and turning the adjuster counterclockwise two turns at a time, testing the vehicle after each change, until part throttle spark knock is eliminated. You might also get light surging if it advances too much. Just back it off till it runs good. Now as far as ported or full vacuum goes.......
 

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I'm still learning the ported and full vacuum part, I've been told ported is what it needs.
 

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With a hot camshaft, 10deg,vacuum advance MAX.
I think the main reason vac advance gets a bad rap with hot motors is the stock cans add too much to go with the 16-18 initial and fast curves these motors love. An adjustable can is a must.
 

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It's a fair size, for a hydraulic .575 lift. I just reread the link on vacuum advance and now understand how to set it up correctly now.
 

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with it at 16 you could run without it just use soft mechanical advance springs, ive ran this way for years on the street with sm/bbc or set inital to 10 or 12 and play with it, everytime i tried hooking it up with an adjustable i got spark knock, i also run a msd6a box with a stock hei and coil.
 

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with it at 16 you could run without it just use soft mechanical advance springs, ive ran this way for years on the street with sm/bbc or set inital to 10 or 12 and play with it, everytime i tried hooking it up with an adjustable i got spark knock, i also run a msd6a box with a stock hei and coil.
I ran a stock HEI with the Vacuum advance with no issues, but this engine will spin 7000 + rpm, a bit more then the stock coil is good for, so I up graded and now have an adjustable can. I'm going to try to dial it in and see what I can get it to do, I'd rather try to get it working if possible. If not, I'll pull it off. I'm not running an MSD box.
 

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Full manifold vacuum to a stock vacuum advance can,no more than "10"deg MAX,on a hot engine on the street. A after market vacuum advance can will work too. For me is the only way! 7500 + rpm's.
 

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The only way to set the vacuum advance is with driving conditions.

You set initial and total.

Plug in the vacuum advance and drive it.

You want the most timing without detonation or temp changes at cruise.

remember acceleration has nothing to do with the vacuum advance.

You can not go by what the timing light tells you with the engine not being at a cruise. It's based on cruise engine vacuum.

When you accelerate the vacuum advance becomes none effective and your engine depends on the total timing of the dist. (as your car is now without the vacuum advance)

The vacuum is hooked to the intake vacuum. The lower port under the front fuel bowl on a Holley.

Al

 

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Not true on only hereing it,pinging can happen that is not sounded to the ear.If all cars were tuned by ear,the people in the know would say so.
 

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My stuff seems to progress from pinging (way too much) to surging and bucking (a little too much) to smooth (just right) as I back off the advance can with the allen wrench. Not to say I don't have any trace rattles going on that I can't hear. I make sure the power valve comes in before I get into the throttle very hard.
 

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In a perfect world, if every day was like the day you tuned it by ear, that would be close if you readjusted idle mixture screws each time you adjusted the vacuum advance can. But with weather change, coolant temp and air temp changing, then that would throw off your tune.
 

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So whats the benefit of vacuum advance if it doesn't help on acceleration and it doesn't take that much power to cruise? Better gas mileage? Does the vacuum advance work at idle? I would think it would since the throttle is closed and vacuum should be higher right? Could you set the initial timing low so it cranks easier, then as soon as it starts, the vacuum advance kicks in to make it idle better?
 
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