[Jack21]

OE CR sidepipe mufflers (1 1/8" inside pipe) would be a restrictive exhaust on a Honda Civic. If you were running a stock '63, 260 2v (164hp), you could probably leave it alone. Anything more, engine wise, and the restrictive muffler kills your performance.

Cut the OE CR mufflers out and replace them with glasspacks. What size? 3" core X 30" length, a little on the loud side, but great performance. 2 1/2" core x 30" length, sound is OK cruising. 2 1/4" core x 36" length, sound is very mellow, but engine feels slightly less snappy.