I'm have a friendly argument with a buddy of mine that runs in the same class as I do.

Our engine limits are 410 CID, cast iron heads, one 750 cfm carb, and 8000 rpms.

The question is, if all things are equal, how much horsepower is gained from a 400 to a 406 to a 410.

I just can't understand taking a new Dart block and boring it right from the start.  

You're going to need to decide how much money you are going to spend. This is a fine line between outright output and durability...

I imagine your Dart block will be perfectly fine at either .040" or .060" over "stock" (I'm not sure which you're talking about). But, your cube limit will not let you bore this engine again when the cylinders become worn. So, depending on the competition, are you going to spend a lot of money to be right on the cube limit all the time to make the most power?

Since you're asking a highly theoretical question (IE all things equal) I will give a highly theoretical answer. Assume that the specific output would remain the same with an overbored engine. So, you could say that the overbore would be worth 8-15 horsepower.  

The reason you'd bore it out is to get your rod/stroke ratio as optimal as possible for the displacement. A bad rod/stroke angle will create more parasitic horsepower loss in the motor, and extra cylinder wall wear.  

"55Guy,"

Did you get up a little too early this morning? The bore has nothing to do with the rod to stroke ratio.  

I would leave it alone you will not gain a hole lot of power boring it out. 400ci to 410 you will probably see around a 10-12 ft.lbs increase with the exact same setup.  

Now, if torque only mattered...  

torque * RPM * constant = hp

   87.5 lbf-ft * 60 rev/min * X = 1 hp

   X = 1 / (60 * 87.5) = 1/5250

   torque * RPM * 1/5250 = hp

   hp = (torque * RPM) / 5250

Or HP + TQ x RPM / 5250

I would say not worth it, save the cylinder walls to be bored another day.

**corrected for grammar  

Thanks for the elementary physics lesson...  

You're welcome.....  

I hope this helped firefarm and thanks Smoke for popping out that equation.