2 1/2" vs 3" Exhaust Comparison Video

yellow rose said
I don't know where this chart comes from, but if take 2 CFM per HP.

I can tell you most of these rule of thumb charts are wrong, and they err way on the small side.

Look at carbs. For DECADES people thought a dominator was too big for everything. Now they are on everything. The charts were always wrong. I don't put much into the above chart either.
Click to expand...

Did you read the full article and see the math he came up with? He figures it out down to the last CFM. I trust that chart as a good guide. But as a general rule when I am stuck between one smaller and one larger size, I go the larger size.