Dwell vs Electronic Ignition
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Thread: Dwell vs Electronic Ignition

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    QuestionDwell vs Electronic Ignition


    Today I fired up my GT and ran some checks. Last year, during my restoration, I converted from points/condenser to Pertronix electronic ignition. I was checking the idle speed with my very old Tach/Dwell meter and inadvertently slid the switch to "DWELL". The scale indicator was about 55 degrees.

    I understand that Dwell is the number of degrees the crankshaft turned while the old points were opened. My question is this: When adjusting the Pertronix trigger amp module to magnet unit clearance with the plastic gauge, am I actually setting dwell? How critical is this adjustment and what actually is being set with the plastic gauge?

    Thanks,
    Paul in Michigan

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    Member My location Dmcbrass's Avatar
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    No, dwell is not adjustable with Pertronix. The adjusting of dwell with points would actually affect the timing and strength of the spark. That's a non technical explanation.

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    3000 Post Club blancojp (R.I.P.)'s Avatar
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    Dwell actually refers to how long the points remain closed, hence time to charge the coil.

    Increasing the dwell causes points to close sooner and open later as it is triggered by the point that rides over the distributor cam. With the Pertronix, you have to consider the actual working angle of the magnetic trigger rotor which is what activates the igniter.

    Let's see if I can explain it better for you.

    The magnet sleeve on the distributor is turning and has 4 individual internal magnets placed at 90 degrees. When the magnet comes close to the Pertronix igniter's center, it opens the circuit and discharges the coil. When the magnet leaves, it closes the circuit and charges the coil. Depending on the strength of the magnet, it can very well take a few degrees before and after the trigger point to release the igniter and charge the coil.

    This is why Pertronix says damage to the ignition coil or igniter will happen if you switch the ignition key on, without starting the engine, for extended periods of time.

    The one's made in the UK by Stealth are better in my opinion. Coil charges when the magnet is in front of the igniter and the magnet is sized for the actual duration. Our igniter on the programmable distributor works the same way.

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    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by blancojp View Post
    Dwell actually refers to how long the points remain closed, hence time to charge the coil.

    Increasing the dwell causes points to close sooner and open later as it is triggered by the point that rides over the distributor cam...

    Back in my younger years I remembered the relationship like a so..

    Increase gap---decrease dwell
    Decrease gap--increase dwell
    hrcollinsjr likes this.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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    Paul, when you posted this earlier, I did a little googling on that subject and found that changing the gap there can increase or decrease dwell time by about 4-5 degrees from the factory (Pertronix) I believe it's not recommended because you run into the chance of the unit hitting the shaft, etc, damaging it.

    The pertronix site itself has a lot of info to check out in .pdf form, worth looking into. But I get the point that it's best just to go with the factory set up and you are good to go.

    Myself, I have a Crane XR-700 and I like it a lot. A different animal then the Pertronix....

    Good Luck,
    Mike

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    7,000 Post Club My location wrench459's Avatar
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    Quote Originally Posted by Paul M View Post
    My question is this: When adjusting the Pertronix trigger amp module to magnet unit clearance with the plastic gauge, am I actually setting dwell? How critical is this adjustment and what actually is being set with the plastic gauge?
    The dwell time is fixed.
    Don't just look at the dwell period at idle speed...rev the sucker up..the dwell time should be
    very stable.
    The air gap is very important....that's the trigger to release/collapse the primary windings.

    Keep in mind this is with a single 3.0 ohm ignition coil.
    Multi-coils with sub-ohm primary resistance is a whole nutter-butter game.
    Last edited by wrench459; 03-12-2015 at 09:17 PM.

    Si vis pacem, para bellum "If you want peace, prepare for war"

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