Would an advanced cam effect what a scanner read for ignition timing?
11-06-2006, 09:45 PM
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Racer
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Would an advanced cam affect what a scanner read for ignition timing?
Here's the simplest way I can think to ask this question:
Theoretically, assuming our stock cams aren't advanced at all, and our stock ignition timing is advanced 25 degrees, and we install a cam with 4 degrees advance built in, would our ignition timing advance to 29 degrees? Would a scanner stilll read 25 degrees when its actually 29?
Probably a stupid question, but the reason I ask is because I don't know if my tuner knew my cam had 4 degrees advance built in and I wonder if this was giving me artifically low advanced timing numbers.
Theoretically, assuming our stock cams aren't advanced at all, and our stock ignition timing is advanced 25 degrees, and we install a cam with 4 degrees advance built in, would our ignition timing advance to 29 degrees? Would a scanner stilll read 25 degrees when its actually 29?
Probably a stupid question, but the reason I ask is because I don't know if my tuner knew my cam had 4 degrees advance built in and I wonder if this was giving me artifically low advanced timing numbers.
Last edited by fovsky; 11-06-2006 at 09:55 PM.
11-06-2006, 10:28 PM
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You're talking about two different timing events. When the cam has advance ground into it you're talking about valve timing events. This has to do with when the valve opening and closing events take place and is used with the centerline of the cam when being installed. Remember, the cam is installed in exactly the same position as the stock cam. In old days, you could advance or retard the cam by using offset bushings in the timing sprocket when the cam was ground straight up.
The other timing event has to do with ignition spark advance and relates to the position of the piston when the spark event occurs. Ignition timing of 28 degrees means that the spark is fired 28 degrees of piston movement before the pistion is at top dead center during the compression stroke. This has absolutely nothing to do with the cam being ground with 4 degrees of advance in it. Unless you changed the timing in the timing table when tuning the car the timing shouldn't be different. Also make sure you're reading the correct timing table at idle as the idle timing table has different timing than the high octane spark table.
The other timing event has to do with ignition spark advance and relates to the position of the piston when the spark event occurs. Ignition timing of 28 degrees means that the spark is fired 28 degrees of piston movement before the pistion is at top dead center during the compression stroke. This has absolutely nothing to do with the cam being ground with 4 degrees of advance in it. Unless you changed the timing in the timing table when tuning the car the timing shouldn't be different. Also make sure you're reading the correct timing table at idle as the idle timing table has different timing than the high octane spark table.
11-06-2006, 11:06 PM
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Thanks vetpet.
I'm getting desperate trying to determine why I can't get more timing before detonation and confusing myself. One less thing to consider.
Now that you've dumbed it down for me its clear that ignition timing is measured from TDC which is tied to crankshaft degrees, and is totally independent of the valves opening and closing which is tied to cam advance. Thanks for taking the time to answer a dumb question.
I'm getting desperate trying to determine why I can't get more timing before detonation and confusing myself. One less thing to consider.
Now that you've dumbed it down for me its clear that ignition timing is measured from TDC which is tied to crankshaft degrees, and is totally independent of the valves opening and closing which is tied to cam advance. Thanks for taking the time to answer a dumb question.
