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Old 09-12-2002, 08:11 PM
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Post Advanced????Retarded???? Im Confused!!!!

Ok, Ever since Ive known of engines, Ive always thought advancing the timing is when you turn the distributer clockwise (on a small block chevy) and the spark occurs just after the piston hits TDC, And retarding the timing was bringing back the timing to right before the piston hits TDC. A few people have really confused me by saying that I have everything backwards. They say since your setting the spark after TDC, your retarding the timing, and when you set the spark right before the TDC, your advancing it. Now this really confuses me on whats advanced and whats retarded. Can someone tell me whats the correct way of advancment and retardation.

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Old 09-12-2002, 08:45 PM
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To advance the timing on a small block chevy, the distributor is turned counterclockwise. To retard the timing, the distributor is turned clockwise. When you advance the timing, you are making the spark fire before TDC. The further it is advanced, the earlier the spark will fire "before" TDC. Retarding the timing is exactly the opposite. If you retard the timing, that means that you are making the spark fire "after" TDC. There are advantages to both depending on your application. Advancing the timing usually increases your off idle acceleration, but you usually give up some RPM's at the top end. Retarding the timing usually decreases low end throttle response but you will gain more RPM's at the top end. So it's a trade off. I like to run my 350 as advanced as possible without detonation and starter drag.
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Old 09-13-2002, 07:18 AM
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The one thing to remember is that very few street engines actually run "after" TDC. What we are talking about is how much "before" TDC the timing is set at. In this case retarded is setting it closer to TDC and advanced is further away. I would consider 6 BTDC retarded on a 350 and 12 BTDC advanced. In either case it fires before the piston reaches TDC.
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Old 09-13-2002, 09:22 AM
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And also consider that the distributor has an advancing mechanism (mechanical or vacuum induced) which advances the timing as RPM's increase. This is done because the amount of time necessary for the flame front to cross the piston becomes shorter as RPM's increase. To compensate for that, the spark is advanced progressively. So typically in a SBC you start with about 12 to 14 degrees of static timing before distributor advance and allow for another 12 to 14 degrees to be induced up to about 4000 rpm, but usually mostly all in by 2500. So your timing light should show you about 24 to 28 total degrees after the distributor advance has done its work. Depending upon what you want your motor to do, you can "re-curve" your distributor to change the rate and maximum induction of timing advance that you want.
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Old 09-13-2002, 09:59 AM
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TO EXPLAIN W/O EVEN USING TDC HERE: THE SBC DISTRIBUTOR TURNS CLOCK WISE AS YOU NOW KNOW. TURNING THE THING COUNTER-CLOCKWISE MOVES THE PLUG WIRE INTO THE ROTATION SO IF FIRES SOONER, I.E. IT IS ADVANCED. DIG :p
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Old 09-13-2002, 11:22 AM
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What you are saying is true. How are degrees of advance figured? It would seem to me that if you are 12 degrees away from the firing point, it would be retarded and if only 6 degrees away from the firing point it would advanced. Like you said the closer the more advanced. But we know that 12 degrees is advanced and 6 is retarded. Not trying to be "retarded" here but I am curious. It is something I have taken for granted for years.

Never mind I think I just figured out my own screwed up logic.

[ September 13, 2002: Message edited by: Mertz ]</p>
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Old 09-14-2002, 01:55 PM
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When I was a kid I remember an old Buick that had an advance/retard lever on the steering wheel, now that's an idea!
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Old 09-17-2002, 11:32 AM
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Mertz: You are confusing yourself by assuming that the the iginition of the power stroke event occurs at a specific time or at a specific degree point in the rotation. It does not, it is a continuous process that begins at the bottom of the intake stroke and is finished at the bottom of the exhaust stroke.

Timing is the event at which the spark begins to be delivered. Multiple spark discharge units even extend the ignition period past this point for more complete combustion. Timing is a variable event because ignition must occur at an optimizing time depending upon how much before top dead center the flame front must be started so that it has time to be complete or nearly complete within the power cycle. The time the flame front has to travel across the piston and ignite most of the fuel is a relatively constant period of time, but the time allowed because of the increasing revolutions at higher speeds is a reduced period of time. Therefore, the flame front must be introduced in the power cycle variably earlier as rpm's increase.

Timing is stated in terms of degrees of rotation from TDC. Advanced is degrees before TDC and retarded is degrees after TDC. Advance and retard are also terms which refer to which direction you are moving the spark. To Advance means to increase the degrees of first igintion from TDC. All motors actually begin ignition before TDC and the flame front is developed beginning before TDC in most cases, however, the power stroke continuse until BDC as the fuel continues to burn and push the piston down on the power stroke.

All we are talking about when we speak of ignition timing is when to start the ignition and usually for a high rpm SBC, we are talking about around 28 degrees before TDC. About half of this is delivered statically by the distributor without mechanical or vacuum advance and the rest is gradually delivered as rpm's increase by the mechanical or vacuum advance.
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Old 09-17-2002, 12:36 PM
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In other words when I move the distributor, I am advancing and retarding the timing depending on which way I rotate it, but the timing is always advanced in a SBC because the ignition is set to fire before top dead center. I assume there are no engines that start firing after TDC. So when I said that closer to TDC is retarded it is only retarded based on the total amount of advance not the firing position after TDC. For example if the specs call for 10 BTDC than 8 would be retarded and 12 would be advanced from spec.

Thanks for making it more clear. I got to thinking about one of the responses and confused myself but like I said I think I figured out my own illogic.
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Old 09-17-2002, 03:07 PM
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You are on track now with you example of 12 being advanced from spec 10 and 8 being retarded from spec 10.
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