OK, so you hear me harp on not running as much timing as you'd like.

So when in a degree not a degree, or what does a degree really mean.

If you think about it for an instant you'll see/ remember that at TDC the piston is changing direct, so it has to slow down some as it does that.

Now for the none MEs (mechanical engineers) take a 6" protractor, and draw a circle. At the top of the circle we'll call that TDC. Draw a line straight up 6" to represent the rod.

From 10 degrees before TDC draw a line 6" long that intersects the first line. See who the piston has moved about an 1/8" in that 10 degrees.

Now repeat that at 20d, 30d, and 40d.

Notice anything?.

40d and the piston is like an inch from TDC.
30d and it's 9/16" from TDC.

When your running the big timing, I hope you can see now, why every degree is an important element.

Then think about if your lighting the charge an inch before TDC think about how much pressure is building as the piston is trying to continue upward. Then think about how much less the pressure is rising when you light the charge just 9/16" from TDC.\

Just food for thought,

 

That is about the best way I have ever heard pistion travel per degree described. You should also be able to illustrate the difference rod length has on piston speed and TDC dwell "time" using different diameter circles (5.7 inch radius for stock rods, 6 inch radius for 6 inch rods, and 5.545? for 400 SBC rods).

Again, excellent illustration.

 

And drawing it out really shows what offset wristpin holes will do for you.

With rod lenght you can look at how fast the piston moves from TDC and better understand how rod lenght effects cylinder filling. A short rod helps alot. It also puts the rod in even more tension thou.