There is some really big differences in header designs for cars that are intended to run with open headers, even just the merge or blended collectors are
way more money than most high quality street/strip so called performance type fully welded complete
mas produced name brand cheaper type "racing headers", the tube diameter, length, tuned equall length tubes with no sharp bends, smooth style tubes &/or type & size of collectors, stepped tubing or Tri-Y's merge tubing or even the length & size of extensions can make a big difference, IMHO if your only picking up 0.1 sec. to 0.15 sec. in ET your probably just reaping the benefits of less weight from the exhaust system not being on the car, not because of being un-capped headers... There is a guy here with a screen name
Perfomance Welding or his company in Forest Hills Ca. @
www.perfweldheaders.com , you guys should visit his site & then you should talk to him, if you really want to run open headers & see the proper ET/MPH gains, he builds custom headers everyday for a living, also make & sells, slip on or weld on collectors, Tri-Y's, merge collectors, cones & extensions etc., for a bunch of Super Stock & Pro guys,
they aren't cheap, but it depends on what you actually want to get out of your ride vs's if your car is a track only car, it's well worth the money HP/TQ gains.... Most performance builders are either trying to peeny pinch or are running out of cash when they get to the headers, but they don't bat an eye at $3500-$5000 on a set of heads & induction/fuel system, a high dollar stroker short block or hot dog high dollar converter trans & rear axle &/or suspension set up, but wont spend the money on the exhaust/headers, to make the other parts work fully to their potential, how they were intended to, or are maybe some are just to cheap or the don't know the actual performance benefits/gains, to spend the extra ca$h on the proper style/type length/design of custom or quality built real
racing headers... If they have a bolt on exhaust flange, the chances are they aren't real racing headers... Good luck guys... Happy Moparing