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Old 06-17-2013, 09:27 PM
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another timing thread

355 sbc 9.5:1 dart iron eagle heads 200/64. i just did a head swap went from stock 882s but short block was already in car so not sure what cam, but it is very street friendly id guess something sub 480 lift. anywho, ive ran the numbers on my dizzy advance plate and weights and i am coming up with about 24 deg mech advance. (375 plate 105 weights)

question is, should i just set the timing at 12 btdc and rock with it, or should i run as much initial as possible, say 16 or 18 deg then tailor the dizzy plate and weights to bring me to 36 deg btdc??

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Old 06-17-2013, 09:29 PM
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and if it matters, eddy performer rpm intake and holley 600 vac secondary carb
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Old 06-17-2013, 10:45 PM
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This Demon carb guide says 10-12 degrees with a mild cam. Click on tabs shown to see spark advance for hotter cams.....
Demon Fuel Systems
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Old 06-18-2013, 08:41 AM
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Thanks tech.
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Old 06-18-2013, 10:44 AM
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12 is pretty low, higher initial can help clean up the idle burn and lower operating temps which is good for stop and go traffic, just one advantage. depends what the car/truck is used for too.

You did not mention vacuum advance? if you are using it and have connected to manifold vacuum at idle your initial is raised to 12 + the vacuum advance amount so you are actaully running more than 12 at idle already

FWIW Yes I would go higher maybe 16-18 and then set the mech advance to limit to 34 ish. This proceedure will make you get in there and have a close look at the dist, clean it up etc, this is always a good plan if you have not already done so. Add 10 or 12 with vacuum advance on manifold try it and see how it works. Dont go over 48 BTDC total with everything in.

2 more of my cents

What type of dist is this we are talking about?
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Old 06-18-2013, 02:30 PM
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Hei distributor in an 85 monte ss. Mainly highway miles but some stop and go traffic. Yes I will be running full manifold vacuum on my dizzy but it's not an adjustable can so I'm guessin about 15 degrees from it. I really don't want to make anymore changes than I have to but if I need to limit my total + vac advance to 48 looks like ill need to start somewhere closer to 8-10 deg initial. At what point is too much initial advance? I will be running oem starter.

Ps, idk why anyone runs ported vacuum. Just picked up an 81 c 10 that was running ported vacuum. Terrible mpg and throttle response. Lousy performance.. Could smell my wallet burning along with the gas. Switched to manifold vac last night and my problems are gone. Swear I can feel it in the seat of the pants too.
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Old 06-18-2013, 02:33 PM
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If I do change up the dizzy to more like 16-18 mech advance what parts kit would you guys recommend? Or am I best off digging around in a junkyard for some different stock plates and weights?
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Old 06-19-2013, 10:36 AM
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In most cases you can limit the mechanical with a simple machine screw (yellow arrow) or nut and bolt that will limit the rotor plate rotation. Depends on the HEI, sometimes you will need bushings to do the same thing but they install over the plate pins. (red arrow)

Weights may change a few characteristics of the mech adv but to limit is to install limits in my book

Crane sells a vacuum advance limiter plate that installs behind the vacuum advance canister rod to limit the amount of vacuum advance. These work and are cheap, or make one up to do the same thing. Second last notch gives approx 12 deg on most cans.
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Old 06-19-2013, 11:21 AM
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When you set your timing and get the initial all set and done try the vacuum advance on ported and full manifold and see how the engine does. There is always a argument on what should be used and honestly I have found out it depends on the total engine combo and the camshaft.

I had my milder 350 on full manifold for vacuum advance and no matter how I set my initial I could not get rid of a off idle backfire so by accident sort off it was put on ported and walla problem solved as it somehow did not like to work well with what my initial was and it was limited to 12-14 degrees for the vacuum advance timing along with the 18 ish I am running initial.

My more wild 350 likes the full manifold for vacuum advance so there is not a concrete way of setting that part so its a trial and error thing and as far as mpg goes off idle the vacuum advance is the same either being ported or full. Only difference is at idle. But that is my experience.
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