other than the obvious size, between a magnaflow 3" SI/SO system and a 2.5" SI/DO system.....as far as sound, performance, mpg???

 

Looks.

There may be a slight difference in sound (given the same muffler design) and two 2.5" pipes have more cross sectional area than one 3". Performance wise? Depends on the motor and other mods. Also depends on how good the two 2.5" pipes are designed because I think the Magnaflow 3" one in the #15609 system is probably the best.

Overall, I think there is less performance risk than a single 3" for mostly stock engines.

 

APT

Do you mean there would be less performance risk going with the 3"? I have a 5.4L stock engine. The only thing I've done was add a drop-in K&N. I don't plan on doing a chip, possible some electric fans down the road.

 

After catalytic changes in exhaust yield hardly any hp changes (at least in 2x2.5" vs single 3") so I think you should make the decision based on how you want your exhaust system to look. Also the dual out 2.5" will be a lil' louder than a single 3"

 

Some people that have gone to a SIDO system have felt low end torque loss. Just seat of the pants, but that is what they feel. Others say it is about the same and others say slight increse. I haven't seen any dyno numbers so I can't say. I have not composed the data of what engine with what mods experienced loss or gains.

I have not heard of anyone with a 5.4" use a single 3" tail pipe regardless of what they did before the tail pipe complain about power loss. That I would have remembered as that is what I will probably do with my 5.4L. That is what I mean by less risk.

I think you can get good results from both. Sccully put on true dual 2.5" Bassani setup on his Screw 5.4L last week. He had a Gibson (forgot which system) before and this is a slictlyy better feel to it, but SOTP is hard to measure.