after the first of the year I will be doing a build on a slant 6 with long rods and 2.2 pistons, cam, 4 barrel and headers! do you think 2 1/2 exhaust would be too big?
Not too big at all from an engine breathing standpoint. Eventually one runs into the bends fitting under the car as the pipe size gets bigger and bigger.
With a narrow lobe angle cam (more overlap), going up moderately on the CR is OK. Even with a wide lobe angle cam for torque, a modest CR increase over stock is OK; a half point in that case will still work and will add to the engine's zip.
