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post #1 of (permalink) Old 08-05-2000, 08:18 PM
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its all about timing

How do you determine the ultimate ignition timing for a modified engine. Does alot of initial advance
provide more lower end torque and throtle response?

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post #2 of (permalink) Old 08-06-2000, 12:34 AM
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Re: its all about timing

YES!
http://www.boyleworks.com/ta400/psp/distcurve.html
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post #3 of (permalink) Old 08-09-2000, 11:59 AM
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Re: its all about timing

Correct ignition timing helps a ton. Especially at idle and low r's. But I don’t agree with the methods used by the website dave recommened.
The method I use is very time consuming, but worth every minute. First you have to lock your distributor (zero mechanical adv), and disconnect vacuum adv. Then you set the timing, I usually start at 15. Now make some short full power starts from a stop to see how low-end power is doing. If there is no pinging then adv to 20, repeat power test. Keep going until you ping or lose power, then dial it in ‘till you find the perfect initial timing for launch (max power, no ping). Now find your max total timing. This is easier because the #’s are usually the same for a given motor, plus or minus a couple of degrees. My 3.75 stroke/400 Chevy likes 32, a 3.48/350 likes 34-36, a 3.25/327 likes 36-38, see a pattern? Also the better the combustion chamber design the less total timing needed, so other brand motors are a little different. With total adv I like to go with the lowest # without power loss. Now that you’ve established initial and total, for instance 20/35, you need to make the mechanical adv in the distributor make it happen. In this case 15 degrees. This can be done different ways. I reduced the original total by filling in the original oval hole that limits adv movement, and redrilling it a smaller size then using a file to get it exact. This was a real pain because I had to use the engine with a timing light to check adv, then remove and disassemble the distributor for each adjustment. Once that is done you get to dial it in using adv springs. You’ll want the adv to start much later than normal because you have a lot of initial already. Same deal applies here with max power and ping. Trial and error to dial it in. Now you’re set for Max power! If you make any changes, especially the cam, this will have to be re-done. If you want to use vacuum adv, it needs to be modified also. Your new set-up is dialed in too close to the “ping” zone to deal with an OEM vacuum adv curve. You’ll need to limit it’s total (usually 20 degrees) to 10-15 and most important, delay it’s onset. On mine I soldered a little bar across the path of the vac adv movement. I bumped it’s start point up about 1/3. This means it will take quite a bit of vacuum to start moving. Lastly, after all this tinkering you need to be sure the rotor matches the contact points on the cap at the moment of firing.


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