I have an 89 CRX with a DOHC ZC. It has an HP Racing 4-2-1 header, no cat with the stock midpipe of the exhaust. I have a Ractive axle back exhaust, the piping from the axle to the muffler is 2.5 inches. I was just wondering what size piping i should use for the midpipe part of the exhaust? Is 2.5 inches to big?? I put the Ractive axle back on it with the stock midpipe and it was backfiring and running like crap, but after i took it off and reset the ecu it runs fine. Is it okay if it blows a 12 inch flame out of the exhaust when i rev it??