Here's a good "laymen's terms" description on the subject: Exhaust Backpressure Myth

 

Your right on that one.

 

well i went to the track and i gained one tenth, 12.1(w/o) 12.2(w) my car is still messing up and is at the dyno as we speak. thanks to everyone who replied

 

Speaking of computer issues with running open headers...keep in mind that running them open can also burn out your front o2 sensors. If there is no extension on the end of the headers, clean outside air can make contact with the sensors and, if its enough, burn them out. If you want to run them open, I'd at least throw 12 -18 inch extensions on them so that the fresh air can get to your front o2's.

 

Camaro69, that link you posted was very well explained. I would highly encourage everyone to read over that in order to further understand what's happening in your exhaust. I think something else that would be beneficial to append to that article is that long tube headers help with exhaust scavenging due to the lower resonant frequency of the longer primaries. After the collector the tubing behind it also effects this resonant frequency and can further lower it, unfortunately this also reduces flow. It results in a decrease in peak HP but a shifting of the torque curve to lower RPM. As has been discussed, this feels like a decrease in power because you lose torque in the lower RPM so you don't notice it as much.

 

awesome article camaro69. I learn something new everyday!