Dwell Question - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 18 (permalink) Old Jul 7th, 20, 12:34 PM Thread Starter
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Bill
 
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Dwell Question

68SS, 4 speed.

Yesterday I discovered my dwell was at 22 degrees instead of 28-32 as called for in maintenance books. The reason was a screw up on my part. My question is would a 6 degree error cause anything in performance that wold be noticeable? I reset dwell and timing and took it for a ride and the only thing I noticed was a stumble I had before when flooring the gas pedal seemed to go away. I would appreciate opinions of board members. Thanks.

Bill B.
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post #2 of 18 (permalink) Old Jul 7th, 20, 12:58 PM
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Re: Dwell Question

When the dwell number is too small, that means the points are too wide. Six degrees retarded could easily cause a stumble.
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post #3 of 18 (permalink) Old Jul 7th, 20, 1:36 PM
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Re: Dwell Question

30 to 32 degrees of dwell seems to be the optimum for the coil to saturation. Get outside of that box and performance will be affected.
I believe the dual point distributors found during the 57 to 61 years use one set of points to close and the other set to open or maybe they both are in parallel and operate together. They were the real deal during their day for high RPM operation but by 1962 Chevrolet was using single point ignition... Al
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post #4 of 18 (permalink) Old Jul 7th, 20, 3:58 PM
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Re: Dwell Question

Set it at 28 and let the points trigger a CD box and you'll have one of the best ignitions going...
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post #5 of 18 (permalink) Old Jul 7th, 20, 7:29 PM
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Re: Dwell Question

Forget using the points to trigger an extra unit, just isn't needed.

Dwell time is the time in crankshaft degrees of rotation that the coil has to absorb current to make the next spark. This is measured in degrees of dwell of crankshaft rotation.

Altered dwell changes the current the coil and ignition system has to make a spark, and out of specification both directions does adversely effect current to the coil, and in some instances, performance, as you found with the hesitation.

What a lot of people either do not understand, or, refuse to accept is that most drop in replacement ignition systems are NOT stronger than the original points systems, they do not have the "driver" electronics to increase the dwell time the coil has to saturate, no matter the voltage inpot of the system, spark plug gap, nor coil used. Simply stated, they are NOT an "HEI', they are a simp0le saturation system, period.

Now, what many people say those systems are, the real HEI (High Energy Ignition), DOES increase coil current saturation between sparks, which does make a significant difference in voltages and currents at the spark plugs, a stronger system.

Even more different is the MSD type CD systems. CD is "Capacitor Discharge", and functions very differently than both points, and their replacement systems, AND the HEI, In a CD system capacitors are used to charge and store current for spark production, and the coil stays "cold", no current input between spark events. Capacitors can charge infinitely faster than dwell systems, and that is why the MSD can produce multiple sparks for a single cylinder firing event. The capacitors charge, then discharge into a voltate free coil, making higher current and voltage output.

These electronic ignition systems fair better with a properly applied magnetic pickup in place of the points. With the MSD, yes, points do wear a lot slower, but, they still need replacing when they wear away the rubbing block against the points cam. Opinions vary, but that is the way they work best.
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post #6 of 18 (permalink) Old Jul 8th, 20, 12:52 AM Thread Starter
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Re: Dwell Question

Quote:
Originally Posted by dyno jonn View Post
When the dwell number is too small, that means the points are too wide. Six degrees retarded could easily cause a stumble.
Thank you, Jonn. That is what I was hoping to hear. I drove the car again today and the stumble is not there anymore. I'm sticking with points since 2 Pertronix systems failed shortly after installation. I just have to learn how to read my dwell meter a bit better.

Bill B.
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post #7 of 18 (permalink) Old Jul 8th, 20, 8:18 AM
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Smile Re: Dwell Question

Smart move Bill. Like I said if you really want to upgrade, just connect any of the many well made CD boxes available to us..

If you keep the points only system, you get to use copper core wires. I like to solder the ends. This makes a set of wires that will last years. Many people don't realize you need to change carbon core wire every 5 years or sooner.. They brake down pretty fast..

Decent dwell meters are always on cragslist. I'd get one that easy to read.
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post #8 of 18 (permalink) Old Jul 8th, 20, 11:49 AM Thread Starter
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Re: Dwell Question

Quote:
Originally Posted by hydro462 View Post
Smart move Bill. Like I said if you really want to upgrade, just connect any of the many well made CD boxes available to us..

If you keep the points only system, you get to use copper core wires. I like to solder the ends. This makes a set of wires that will last years. Many people don't realize you need to change carbon core wire every 5 years or sooner.. They brake down pretty fast..

Decent dwell meters are always on cragslist. I'd get one that easy to read.
I bought a Innova 5568 timing light last week that has dial back timing advance, rpm, volts and dwell incorporated in it's digital screen. Seems like a good tool and that's how I found my dwell off by 8 degrees. My old dwell meter that I bought at Montgomery Wards many years ago was the reason I set the timing wrong because I misinterpreted the 6 and 8 cylinder reading that was on the same scale.

Bill B.
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post #9 of 18 (permalink) Old Jul 8th, 20, 12:56 PM
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Re: Dwell Question

Dial back is beautiful, FOR EFI COMPUTER TIMING OF THE IGNITION CURVES, but totally inaccurate for mechanical/vacuum advance curves.

Answer a question, all you that know more than the people that build them, how do you "compensate for lag" in a timing system that does not use a computer and inputs (that creates timing lag", on a system that does not have a computer, does not create a timing lag??????????????????

Lets hear it all.

The right answer is: Analog timing does not create a timing lag, as it does not have a computerized timing curve, it is all done with weights, center, springs and vacuum advance. LEAVE THE DIAL BACK OFF FOR ANALOG (MECHANICAL/VACUUM) ADVANCE USE.

Enjoy the inaccuracy.
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post #10 of 18 (permalink) Old Jul 8th, 20, 1:00 PM
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post #11 of 18 (permalink) Old Jul 8th, 20, 4:15 PM
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Re: Dwell Question

Quote:
Originally Posted by Dave Ray View Post
Forget using the points to trigger an extra unit, just isn't needed.



Dwell time is the time in crankshaft degrees of rotation that the coil has to absorb current to make the next spark. This is measured in degrees of dwell of crankshaft rotation.



Altered dwell changes the current the coil and ignition system has to make a spark, and out of specification both directions does adversely effect current to the coil, and in some instances, performance, as you found with the hesitation.



What a lot of people either do not understand, or, refuse to accept is that most drop in replacement ignition systems are NOT stronger than the original points systems, they do not have the "driver" electronics to increase the dwell time the coil has to saturate, no matter the voltage inpot of the system, spark plug gap, nor coil used. Simply stated, they are NOT an "HEI', they are a simp0le saturation system, period.



Now, what many people say those systems are, the real HEI (High Energy Ignition), DOES increase coil current saturation between sparks, which does make a significant difference in voltages and currents at the spark plugs, a stronger system.



Even more different is the MSD type CD systems. CD is "Capacitor Discharge", and functions very differently than both points, and their replacement systems, AND the HEI, In a CD system capacitors are used to charge and store current for spark production, and the coil stays "cold", no current input between spark events. Capacitors can charge infinitely faster than dwell systems, and that is why the MSD can produce multiple sparks for a single cylinder firing event. The capacitors charge, then discharge into a voltate free coil, making higher current and voltage output.



These electronic ignition systems fair better with a properly applied magnetic pickup in place of the points. With the MSD, yes, points do wear a lot slower, but, they still need replacing when they wear away the rubbing block against the points cam. Opinions vary, but that is the way they work best.
Actually to be technically correct, dwell is specified in distributor degrees

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post #12 of 18 (permalink) Old Jul 10th, 20, 4:48 PM
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Re: Dwell Question

Odd, it isn't that way with other points systems, like single point, single cylinder systems. On all 5 of my Sun Distributor machines, if I set a dwell to 30 degrees on the dwell meter on the machine, then add a portable dwell meter, one that is used to set dwell on a vehicle, the SAME dwell comes up.



And, when checked with a degree wheel, both on the machines, and on the car, dwell isn't different, and goes by degrees of crankshaft rotation, but, you do it any way you care to.



But, the main point is, points need to be set to the OEM specification, ON THE ENGINE, not altered, and especially not changed if some super tuner comes up with a very off the wall dwell spec.
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post #13 of 18 (permalink) Old Jul 10th, 20, 5:10 PM
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Re: Dwell Question

Quote:
Originally Posted by Dave Ray View Post
Dial back is beautiful, FOR EFI COMPUTER TIMING OF THE IGNITION CURVES, but totally inaccurate for mechanical/vacuum advance curves.

Answer a question, all you that know more than the people that build them, how do you "compensate for lag" in a timing system that does not use a computer and inputs (that creates timing lag", on a system that does not have a computer, does not create a timing lag??????????????????

Lets hear it all.

The right answer is: Analog timing does not create a timing lag, as it does not have a computerized timing curve, it is all done with weights, center, springs and vacuum advance. LEAVE THE DIAL BACK OFF FOR ANALOG (MECHANICAL/VACUUM) ADVANCE USE.

Enjoy the inaccuracy.
All the dial on the back of the timing light does is change the scale internally within the gun in which the light fires so you can use a stock indicator without a timing tape that does not read up to the advance your trying to reach. If you set the dial to 20 and adjust your timing so the marks line up at 0, you have 20* of advance set. It does not effect the way the distributor or the engine timing works. It has nothing to do with lag in the ignition system. The dial back timing light has been around long before EFI and computer controlled timing. I've used my Craftsman timing light for 40+ years and the timing reads the same if checked at 0 or 18-36 set in the dial depending on what advance I'm looking for.
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post #14 of 18 (permalink) Old Jul 11th, 20, 12:54 AM Thread Starter
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Re: Dwell Question

Quote:
Originally Posted by oldcutlass View Post
All the dial on the back of the timing light does is change the scale internally within the gun in which the light fires so you can use a stock indicator without a timing tape that does not read up to the advance your trying to reach. If you set the dial to 20 and adjust your timing so the marks line up at 0, you have 20* of advance set. It does not effect the way the distributor or the engine timing works. It has nothing to do with lag in the ignition system. The dial back timing light has been around long before EFI and computer controlled timing. I've used my Craftsman timing light for 40+ years and the timing reads the same if checked at 0 or 18-36 set in the dial depending on what advance I'm looking for.
I just bought my first dial back timing light last week. I checked timing with dial back dialed in, dial back at 0 and my old timing light. They all read the same. The new timing light has dwell, rpm and volts as well as timing advance, I checked dwell with the new light and my old dwell meter and they both read the same. I'm satisfied with my new light.

Bill B.
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post #15 of 18 (permalink) Old Jul 11th, 20, 5:20 AM
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Re: Dwell Question

Quote:
Originally Posted by billbonn80 View Post
I just bought my first dial back timing light last week. I checked timing with dial back dialed in, dial back at 0 and my old timing light. They all read the same. The new timing light has dwell, rpm and volts as well as timing advance, I checked dwell with the new light and my old dwell meter and they both read the same. I'm satisfied with my new light.

Bill B.
Bill, and which timing light was that?
Would you share a link with your Team Chevelle Brothers?

I did find this from a search DIGITAL AUTOMOTIVE TUNE UP METER

it discusses Dwell, scroll down until you see it.


LINK



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