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Old 10-14-2008, 07:10 PM
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Your 383 with a comp 280H 230-230 .480" 110LSA Magnum cam will want 24deg intial static timing at idle.
To achieve that you need to modify the distributor mechanical advance travel limit to limit the mechanical advance to around 10 to 12deg of internal mechanical travel. This will allow 24deg at idle and 34 to 36 deg at max rpm, full mechanical advance.
This modified advance curve will maximize and stablize the idle manifold vacuum, idle quality both in and out of gear and off idle throttle response.

This usually requires disassembly of the distributor and modifying the mechanical advance mechanism stop limit pin slot. (shorten the slot length)
You cannot usualy do this using available "advance curve kit" springs and stop bushings, alone.
Once done, this set up provides a much more stable ignition advance curve than the typical light advance spring+ vacuum advance method. Especially for auto trans cars.
You'll be using a medium/light spring tension on the advance which is much more stable.

So how do you run 24deg static timing at idle and start the motor when hot?
You have two good solutions that you can use together or separate to allow you to start the engine when hot without starter strain.

1. Install a MSD "Starter Saver" auto cranking ignition retard control box to retard the spark while the motor is cranking over and starting. Full timing is restored once the motor achives 500+rpm idle speed.

2. Install a simple dash mounted ignition power interupt toggle switch on the HEI power wire or the MSD box power switching wire, to disable the spark power during hot cranking. Crank it over with the spark power off, count 1-2-buckle my shoe... then throw the spark switch and it will fire easily.
Both methods work.

Once the advance curve is dialed in properly as outlined and the carb throttles are readjusted, you would have plenty of manifold vacuum to operate the power brakes safely and consistantly. Check you power brake booster, check valve and vacuum hoses for leaks.
You'll likely need a 4.5" rated power valve in a holley carb.
You should be using a high stall (2800-35000 rpm) torque converter.
A "stock stall" torque converter puts too much hydraulic torque load on the motor while idleing in gear with the big cam and reduced available manifold vacuum.. which results in excessive throttle opening at idle to over come the idle load torque, further reducing the manifold vacuum and vac adv timing at idle.

While this advance curve setup does not depend on vacuum advance at idle to get idle timing and idle quality, any vacuum advance you happen to get at idle is just a bonus.
I find a adjustable 10-12 deg vac advance canister and ported vacuum to work best overall.
All timing, carb idle mix and speed adjustment is done with vacuum advance disconnected. Then, re-connect the vacuum advance hose to the distributor.

Last edited by F-BIRD'88; 10-14-2008 at 07:29 PM.
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