Dial back timing light and curve question - Chevelle Tech
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post #1 of 10 (permalink) Old Jun 17th, 19, 12:32 PM Thread Starter
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Ron
 
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Dial back timing light and curve question

Checking the timing on my Chevelle with a dial back timing light. I set initial at 18*, I turn the knob on the light to 20, rev the engine to 2000rpm the mark is at about 0*. rev it up to 3000 it stays at 0*. So, am I getting 20* mechanical degrees and a total of 38* (not including vacuum advance, unhooked)?

70 Chevelle SS396 (496) Straub roller, 700r4
69 Malibu convertible (sold)
95 Z28 Convertible T56 6 speed
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post #2 of 10 (permalink) Old Jun 17th, 19, 12:52 PM
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Re: Dial back timing light and curve question

On a dial back light, you have 2 options. Set it to ZERO on the knob and it will SHOW 20 degrees on the balancer. Set it to 20 on the knob and the balancer will SHOW 0.
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post #3 of 10 (permalink) Old Jun 17th, 19, 2:26 PM
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Re: Dial back timing light and curve question

First off, what exactly do you have for a distributor and type of advance?

If you have a distributor that has NO mechanical, and/or vacuum advance, then, YES, the dial back feature will give you accurate settings reports on dial back.

If you have an analog system, with functional mechanical and/or vacuum advance, then, NO, THE DIAL BACK FEATURE IS NOT ACCURATE TO READ TIMING.

Now, I KNOW there will be people on here that dispute that last statement above, but, I ask them to point out just where the "computer lag" is that a dial back feature compensates for when reading timing, please.

Here's a clue, EFI computers use inputs, throttle position, EGR, and the rest of the sensor inputs to literally compute just when to make the next spark event, ANALOG SYSTEMS, the ones NOT locked out, that still use mechanical and/or vacuum advance. DO NOT HAVE A COMPUTER LAG TIME TO COMPENSATE FOR, NONE, ZIP, NADA, NOPE, NYET, they read a straight on, non-processed spark event.

Now, it is a very simple thing to take a piece of chalk, set the dampener to 10 degrees, and make a new line at TDC, and do it again, 3 more times, that gives you a TDC line, plus 10, 20, 30, 40 50 degrees to read, WITH THE DIAL BACK FEATURE OFF, OFF, OFF......OFF. Reading the lines is dirt simple, 2nd line reads at 6 degrees, timing is 26 degrees, 4th line at 2, 42. Even the Geico caveman can do it.

There is no dial back feature that when in operation, reads an analog system properly, NONE, PERIOD. Is it worthwhile to have a timing light with a dial back feature, YES, if you ever go to electronic timing, it will be a benefit, but if not, leave it off, and read the antique timing curves right, with the dial back OFF.
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post #4 of 10 (permalink) Old Jun 17th, 19, 4:14 PM
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Scott Foxwell
 
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Re: Dial back timing light and curve question

Answer to your question is a simple Yes. Having said that, I don't trust dial back timing lights, even my Snapon. If your damper isn't marked far enough, it would be better to get a tape for the diameter of your damper and check from zero for total advance. Other than that, you're spot on.
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post #5 of 10 (permalink) Old Jun 17th, 19, 4:20 PM
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Re: Dial back timing light and curve question

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Originally Posted by steelcomp View Post
Having said that, I don't trust dial back timing lights, even my Snapon.

I agree 100% I don't own one but know of at least two instances where they were used and were nowhere near correct.

Bill Koustenis
Advanced Automotive Machine
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post #6 of 10 (permalink) Old Jun 17th, 19, 4:54 PM Thread Starter
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Ron
 
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Re: Dial back timing light and curve question

Thanks guys, its just a basic HEI style distributer that had a "performance" curve put in it before I got it. The centrifugal advance comes in pretty quick, its all in by 2000rpm. I have a timing tape but its hard to see, these old eyes aren't as young as they used to be. The car runs great but I want to back the timing down a little because it has a tendency to ping at times. 10.3:1 compression.

70 Chevelle SS396 (496) Straub roller, 700r4
69 Malibu convertible (sold)
95 Z28 Convertible T56 6 speed
TC #54 Gold



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post #7 of 10 (permalink) Old Jun 17th, 19, 10:41 PM
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Re: Dial back timing light and curve question

My dial back light is repeatable and I have checked it at 0 and checked it dialed up to 35 and with a marked balancer and it reads the same.

Now like said yours may not.. that is beside the point I will get to.
Many engines will like a different curve and different total advance.

As long as your light will repeat the same timing day after day you can tune with it.
I keep dialing in timing and testing the results by driving.. then check it with the light to see where i am at.

I can go back to that timing it likes best if the timing light is repeatable.

But i never assume it is really 35 total which does not really matter if it wants more.
I give it what it wants.
It was many years before I ever got a timing light..I spent many years porting heads before i stuck some on a flow bench.

Port and test.. remove from engine port some more and test.
Like tweaking carbs..I have done some strange things to a Q jet.. some things made them into junk. But i found what does work for me.
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post #8 of 10 (permalink) Old Jun 18th, 19, 8:03 AM
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Scott Foxwell
 
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Re: Dial back timing light and curve question

One thing to remember... it's what the engine wants that counts, not what the timing light says. Verify TDC. Make sure that wherever you set your timing, it's what the engine likes, not what a book says and If you change ignitions, re check your timing. I've seen 7* difference between similar MSD boxes and as many between different makes of ignitions. They're all different.
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post #9 of 10 (permalink) Old Jun 18th, 19, 1:07 PM
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Re: Dial back timing light and curve question

Let's see, ONE dial back is just fine with an analog timing situation, THAT DOES NOT HAVE ANY COMPUTER LAG THAT THE DIAL BACK HANDLES, and is "dead on". NOT, dial back has, is, and will never, not now, never will be accurate on a system that doesn't have the computer computation the light needs to be accurate.

Sorry, I own three extremely good quality dial back timing lights, one that actually has info that says the DB is ONLY for computer timing functions, trhe other two have a warning to NOT try to use DB on conventional vacuum/mechanical advance systems because the light will not be accurate on Dial Back.

All 3 have proven to be absolutely accurate on DB when a computer times the engine, but as noted, not even close on an analog system.

From my own experiences, and what these light makers had to say, I'll keep on reading the balancer timing tape, setup degrees lines for analog, and for my EFI cars, DIAL AWAY. YOUR RESULTS WON'T VARY FROM THIS.

I proved it to myself, the extreme over hype sales misinformation about Dial Back and analog systems are only there to sell more product.
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post #10 of 10 (permalink) Old Jun 19th, 19, 8:48 AM
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Re: Dial back timing light and curve question

Quote:
Originally Posted by steelcomp View Post
One thing to remember... it's what the engine wants that counts, not what the timing light says. Verify TDC. Make sure that wherever you set your timing, it's what the engine likes, not what a book says and If you change ignitions, re check your timing. I've seen 7* difference between similar MSD boxes and as many between different makes of ignitions. They're all different.
This is most important. Its like tire pressure gauges. As long as its repeatable and you use the same one all the time, go with the value that it reads at peak power.
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