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Discussion Starter #1
I've been driving around without my vacuum advance hooked up, mostly because I've heard so many urban legends about them killing power.

I finally decided to hook the thing up (to FULL manifold vacuum) before my road trip to Hot August Nights- about a 4 hour drive on the highway.

My gas mileage shot up from around 10 mpg to nearly 17!

That's with a 4 speed, 3.70 gears, a 306, 650 DP, and a fairly aggressive cam. Speeds varied between 65-75 MPH. Based on my research, full manifold vacuum seems to be the hot ticket for the advance. Needless to say, I'm stoked.

Moral of the story, hook up that vacuum advance :) It improves gas mileage and does not affect performance whatsoever, as the vacuum advance returns to zero when you're approaching WOT.
 

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I've got my advance hooked to ported by I may test with full as I am trying to tune idle with a more aggressive cam.

What are your cam specs? What is your initial/total timing values (without vacuum advance hooked up), and what is your idle rpm?

These might help with a starting point. thanks!
 

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Oh come on, surely there's SOME way to argue about it. :)
 

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This is one of the most "beat to death" subjects in the car speak kingdom.
This being stated, my engine, whether fact or fiction, likes full manifold vac. I ain't mess'n with it!
 

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Discussion Starter #11
I've got my advance hooked to ported by I may test with full as I am trying to tune idle with a more aggressive cam.

What are your cam specs? What is your initial/total timing values (without vacuum advance hooked up), and what is your idle rpm?

These might help with a starting point. thanks!
Full manifold vacuum improved my idle quality significantly, I actually had to back down on the throttle blades to lower the idle a bit.

It's been a while, but I believe my timing is set at something around 16-17 initial and 35-36 total.

Cam specs are .571/587 lift 231/239 duration @.50 110 LSA. Idle RPM is around 650-700 RPM.
 

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Yep, correct, I haven't had a distributor diaphragm go bad in a long time, but I know one day that 50 year old part will go TU and the kid at the parts house is going to scratch is head wondering what on earth it is.

Lol, isn't that the truth. It's funny as there's more and more generation gap from when these cars were new to today. Like if mankind disappeared and aliens came they would think a TV was some sort of temple icon that we sat around and worshipped or toilet seats were an ornament we wore around our necks.
 

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Yep, correct, I haven't had a distributor diaphragm go bad in a long time, but I know one day that 50 year old part will go TU and the kid at the parts house is going to scratch is head wondering what on earth it is.
A few weeks ago I went to the junk yard and got a few things, one of which was the air cleaner assembly for a carbureted 1987 F150. The girl at the check-out counter looked at it and asked me "what is this?" I had to explain to her what a carburetor and its air cleaner were.
Lord, I must be getting old!
 

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Oh come on, surely there's SOME way to argue about it. :)
Since im feeling contrarian lately, I like my ported advance. I have tried to tune for full vacuum a couple time and can't get it to idle below about 900 and my gitty-up is gone. Ported I idle about 5-600 and can induce whiplash.
What am i doing wrong?:grin2:

Is the OP saying he was using ported prior to this? If so and the blades were open the port was open. When your carb is right you shouldn't need any throttle open at all to idle well:)
 

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^I've had the same experience. I have tried full vacuum in both my 67 C10 and the 65 Mustang and each case I went back to ported for a better idle, running condition.

Full manifold vacuum advances the timing at idle whereas ported should have zero affect on vacuum advance. In my mind it's easier to tune a car with less variables and with zero vacuum advance at idle I can get my car to run better and more consistent?
 

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I've always found street driven cars to run significantly better, in more ways than one, when deploying the benefits of vac. advance.
 
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