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One apex at a time
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Ignition Timing & TDC
That is the ignition timing at idle? I know how to put a motor at TDC with the marks on the cam and the Flywheel. Just for the heck of it I decided to put a timing light on my car. I was actually not expecting to see mark on the cam or the crank as I figured that the ignition timing at idle would be around 8-10 deg BTDC thus the mark would not be visible. TO my surprise I could see the marks on the crank and the cam and they were in perfect alignment with the TDC marks. Does this mean that the motor is idling with 0 deg of timing? I suspect this is incorrect. So what gives?
I am going to next index tdc on the #1 cylinder using a wooden dowel through the spark plug hole to see what actual TDC is and how this correlates to the marks on the crank and cam. The reason for this is I am installing a Megajolt on my car and need to set the car to exactly TDC to properly index the trigger wheel. I was going to go by the marks but after putting the light on it am am going to have to physically find it with the top of the piston. Ohya this is for a 8V na motor in my 924s Last edited by Dean924s; 11-20-2008 at 10:55 AM.. |
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11-19-2008, 07:27 PM
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When you have a dowel in cyl #1, and it reaches it's highest point before going downwards again, the camshaft mark on the cam gear will line up with the mark on the aluminum belt cover thingy. This is TDC. Those are not timing marks, they are TDC marks. This is the top of the intake stroke.
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11-19-2008, 08:43 PM
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One apex at a time
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Quote:
So I ask again what is going on with this do these cars idle with 0 deg if timing advance? |
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11-20-2008, 10:54 AM
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Your timing light doesn't have an advance dial turned on it, does it?
If not, then, well I have no clue.
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11-20-2008, 12:12 PM
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One apex at a time
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Nope it is a 35year old sears unit. No dial or other adjustments to screw me up. Dumb as a stump simple one I got from sears 30 years ago. I am going to have to manually see where TDC is on my motor with a dowel through the spark plug hole and see how that lines up with the marks.
Maybe it does idle at 0 deg ignition timing. I really doubt it but you never know. |
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11-20-2008, 12:24 PM
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According to this thread timing maps
a turbo's idle timing is 4.7 degrees at an idle of 880rpm. I would think the NA is the same at that speed.
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11-20-2008, 12:31 PM
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OK that explains allot as this would equate to only 2.35 deg of timing on the cam and that would be virtually the width of the mark on the gear. If your head is milled or your belt is a bit out of spec you could easly have 0 deg of timing at idle.
Very interesting!!! Thank You!!! |
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11-20-2008, 02:04 PM
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