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 Initial Timing method 
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Joined: Wed Feb 13, 2013 4:04 pm
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Whats the best method or approach in finding the best initial timing for an engine with a decent sized cam?

Hysteric


Tue Feb 10, 2015 8:51 pm
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Joined: Wed May 29, 2013 6:12 pm
Posts: 34
As much as the engine will tolerate and still reliably restart when fully heat soaked.

If you have an ignition interrupt switch and heat soak ins't an issue, then advance timing until vacuum stops increasing.

Not sure if it is the "right" methodology but works for me.


Wed Feb 11, 2015 6:54 am
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Joined: Fri Feb 08, 2013 5:50 pm
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A lot depends on how hard it's loaded and at how low the RPM is. Higher loads and lower RPM need less timing, lower loads and higher RPM take more. I see for the most part that cars with the stall speed up close to and over peak torque will usually run best with locked timing. When the stall is much lower the load is higher, and timing needs are less until the RPM climbs.


Wed Feb 11, 2015 12:03 pm
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Joined: Wed Feb 13, 2013 4:04 pm
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In my case its a street strip 360 ci small block chrysler with a 243/245 @ .050 112 lsa solid cam with around 10.5-1 comp with 3200 stall

Is it as simple as advancing it till i get the highest vacuum reading or until i get the starter begins to kick back?

Im more interested in the actual method people use to find what they think is their ideal initial timing also if the combo requires alot of initial timing would that not just tell me that its lean at idle and requires more fuel from the idle circuit?

Hysteric


Wed Feb 11, 2015 6:02 pm
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It's usually giving it as much initial as it will tolerate without knock issues at operating temp and lower RPM's and with the fuel you plan to use. I would suspect somewhere between 20-25 initial, 30-35 total, and possibly a vacuum advance plumbed to the manifold with a a limited amount of timing added. Maybe 8-10 degrees with the vacuum can.


Wed Feb 11, 2015 6:28 pm
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Joined: Wed Feb 13, 2013 4:04 pm
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That's close to what i had in mind. I'm at 18 initial atm with a black bushing in the msd dizzy to keep the total timing down to 36 degrees.

The Msd doesn't offer allot of tunability.

Hysteric.


Wed Feb 11, 2015 6:49 pm
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Make your own bushings.


Wed Feb 11, 2015 7:01 pm
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I have before but im not really a fan of the msd i currently have as it has no provision for vacuum advance so i bought a Mallory 32 series but as luck would have it its missing some plastic bushes.

Hysteric


Wed Feb 11, 2015 7:53 pm
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Depending on valve timing, most engines will exhibit a distinct threshold of minimum initial advance where the vacuum reaches as high (intake pressure is lowest) as it is going to get at the particular RPM and load (torque converter?) and advancing beyond that point does not increase the vacuum much or at all.

Below this threshold the vacuum diminishes more rapidly with each degree of retard than above the threshold. In many engines 18° is the spot and less than 18° will exhibit much larger RPM drop when the trans is put in gear.

Besides hard starting, too much initial will make the engine misfire and idle rough(er).

The way to find the best or acceptable initial is move the timing in 2° steps and carefully readjust the carb idle speed and mixture screws with each timing change to determine the amount of advance which gives the least RPM drop when the trans is put in gear and the most stable idle when the trans is in gear.

A vacuum gauge is useful because configuring the tune-up to have higher vacuum at the same speed and load indicates the same power is being made with less air and fuel, so the combustion is more efficient, at least by the definition “best power with least fuel consumption”.


Wed Feb 11, 2015 9:18 pm
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Joined: Wed Feb 13, 2013 4:04 pm
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Thanks Tuner thats pretty much the way ive been going about it.

Hysteric


Wed Feb 11, 2015 9:49 pm
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