Mainly because a stock 4cyl wouldnt make good use of it. Dual exaust is application based and most dual exaust designs are utter crap. So in the end if you modify a 4 cyl its better to just have a 3 inch pipe straight through. Some dual exaust designs involve a v6, and the exausts are split 3 to a pipe and each running to a cat. Its kinda pointless to run a 4 cyl to a cat then split it and having having a 4 - 2 and connecting to two cats would cause more back pressure then anything because there isnt as much flow as a v6. Most dual exaust designs are iffy on v6's as well. But in the end it all depends on application.

 

thanks for the knowledge

 

dont mean to dredge up an old topic, but im getting the itch and i havent modded my car in one week. I have an 04 EX 4Cyl 2Dr. And what i want to do next is headers and exhaust, from what im reading its better to go with a single pipe rather than the dual. If i were to get the exhaust system custom made to make the split less drastic would that increase HP? or not a noticeable amount? While im at it, the headers i want to get are the ceramic ones, do they really disperse the heat better? or would i be better off getting the stainless steal ones?

 

ceramic headers do disperse heat much better than steel, and just use the single exhaust..like everyone has said it just increases backpresure and you will lose HP and clog the emissions.