Does rpm affect timing? Does idle timing stay the same as rpm increases? I tried to research it but found nothing, thanks

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by toooslow &raquo;</TD></TR><TR><TD CLASS="quote">Does rpm affect timing?</TD></TR></TABLE>RPM and load both affect spark timing.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by toooslow &raquo;</TD></TR><TR><TD CLASS="quote">Does idle timing stay the same as rpm increases?</TD></TR></TABLE>When RPM increases, it's not idling any more, so I'm not sure what your question reall means.
Running with no load at, say, 2500 rpm has different spark timing than running with no load at 750 rpm. Running at 2500 rpm with a load (like actually driving) has another different timing.

 

im just trying to understand if there is a way to calculate the timing the differences in rpm and load. I know that idle timing for me is 14 degrees. Would it ever go higher than that? When would be the highest point of timing the engine would see?

 

What do you mean calculate it? The ECU stores a map of spark timing for rpm & load, but it's not available for the normal user to see. Unless you talk to someone who programs chipped ECUs, the answer is gonna be vague.

Generally the timing advances for both rpm & load. So the point with spark timing MOST advanced would be redline & WOT.

 

sorry if what i was trying to ask came out wrong. The reason that im asking this is because i just had a b20vtec built, it is very close to passing smog but timing needs to be bumped up one point. Currently timing is 13 degrees, it needs to be at least 14. the concern is clearance issues. stock block, gsr head, and ctr cams. so if your saying that timing gets advanced at wot and redline, it goes way over 13 degrees, then i should be safe bumping it up one point.

hope that helps clarifying. thanks for the input

 

1.) Ignition advance increases as a function of rpm (general trend).
2.) Ignition advance decreases as a function of load (general trend).
3.) Ignition timing has no effect on physical clearances.....except in the case where you have to advance the intake cam to be able to hit your target ignition timing (this could be for a number of reasons; shortened deck height being one of the most common).
4.) Ignition timing can should only be properly measured at the rpm specified by the service manual, otherwise you will be reading it incorrectly. In the case that the idle is high, then you'll read a false high.

 

Ok got it, i think. ignition timing will have no effect on clearances because its just the timing of the spark. But cam timing does. As long as i left my cam gear settings alone, i could advance or retard my ignition timing as much as i wanted without having to worry about clearances.right?

 

Right.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">3.) Ignition timing has no effect on physical clearances.....except in the case where you have to advance the intake cam to be able to hit your target ignition timing (this could be for a number of reasons; shortened deck height being one of the most common).</TD></TR></TABLE>If you have to adjust your cam sprocket, then you've changed both spark timing AND cam timing. So it's still strictly true that SPARK timing doesn't affect clearances.

I didn't realize you were worried about valve/piston clearances...

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by toooslow &raquo;</TD></TR><TR><TD CLASS="quote">Ok got it, i think. ignition timing will have no effect on clearances because its just the timing of the spark. But cam timing does. As long as i left my cam gear settings alone, i could advance or retard my ignition timing as much as i wanted without having to worry about clearances.right?</TD></TR></TABLE>If you put your spark timing really stupidly far advanced, you can worry about detonation & other stuff that can cause damage. But that's not the same as physical clearances.

 

just to add; the whole idea about timing is to END the timing event(explosion) from lets say 15 to 20 degrees after TDC.
the more rpm , the move timing you need in order to still Finnish the explosion at the same time; since you have less time to complete it.
more load less timing because your allowing more air to enter the engine by pressing on the gas, thus the explosion takes less time to complete.
denser air = faster flame propagation