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Old 05-06-2006, 11:49 AM   #1
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Join Date: Jan 2006
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Car: 85' TA
Engine: 355 Carbed
Transmission: Built 700r4

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Removing Vacuum Advance and timing question...

first question-
what is the best way to go about removing vacuum advance?

Can i just not hook it up? I would love to be able to jb weld the vacuum advance assembly shut and go on. Is this possible? or maybe wiggle loose after time?

second question-
I was recomended 18* initial timing, and 36* at full throttle. Does the mechanical linkage only have 18* travel? or will i have to limit the travel it takes?

third question-
With a 355, cam is .520/.544 lift and 234/244 duration @.050. I have a edelbrock performer rpm, and a Speed demon carb, what are your recoomendations as to initial timing for best responce, as well as keeping it streetable.

I did have a previous post about timing, and thats where the 18* was suggested. If it stands, then great.
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Old 05-06-2006, 12:08 PM   #2
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You can unhook the vacume from the advance and plug the vacume source. You'll need to check your total mechanical advance, I think they vary. I know my mechanical advance is 24* and I want to limit it to 16 -18*. You'll need a timing tape or one of those fancy timing lights to accurately check. With your base up that high you'll need a better starter than the stock one. FBird88 has a couple real good posts on here about that stuff. I also think there was something about using the vacume advance for better miliage when there was little load on the engine( cruising speed). Hopefully someone smarter chimes in.
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Old 05-06-2006, 09:32 PM   #3
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Join Date: Jul 2004
Location: Calgary, AB, Canada
Posts: 10,763
Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73

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yea, I certainly wouldn't get rid of vacuum advance, your highway mileage will suck, your plugs will carbon up fast, etc.

You just need to dial in the right timing curve. I'd recommend an MSD 960001 or whatever it is, the fully adjustable vacuum can. You can limit your max vacuum advance, change what vacuum level it comes in on, and that kit comes with mechanical advance springs, to choose when that starts coming in, and when it finishes.

You may want to hook up your vacuum advance to manifold vacuum, that'll give you more advance at idle. Or you can use ported, and bump up your base timing, then weld your mechanical advance slot shorter. (IMHO manifold vacuum is easier ) however you may end up with your manifold vacuum giving you a hunting idle, kinda depends on the motor. Best bet is to try a few combinations and see what works best for you.

that timing (18 base, 36 total) is probably a good starting point. I think stock mechanical is around 20* travel. Lots of different ways to skin the cat here.
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oh right, and say you went 18* initial (that's mostly a guess and check thing), then 36* "total" (that's pretty much the same for most SBC motors.), then you could use around 52* at cruise. Yes, that's right 50* degrees of timing at cruise. If you had that much at WOT you'd ping, but at light loads like cruising, it's ok. Hence, vacuum advance.

Last edited by Sonix; 05-06-2006 at 09:35 PM. Reason: Automerged Doublepost
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Old 05-06-2006, 09:32 PM
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