It is very simply why the Xerds are better, they are LONG-TUBE Headers. The others are all shorty headers. The longer the tube, the more the torque plus shallower bends for more top end HP. Unless they mess up badly on the flange aligments or welds, there is no way a shorty can keep up. Long-tubes will always make more power over shortys. This is simply physics by gas and pressure laws. Look at the number of tight bends on the Crawfords to make them equal length headers. The Xerds because of the longer tubes have a lot less bending necessary to keep the tubes equal length and reach the collector. Despite the bends, the equal lengths will out flow an unequal of the same tubing size by separating the exhaust pulses. Exhaust pulse collision is a higher restriction than a bend. Every bend is still a restriction that will create backpressure. This is why the Crawfords should be better than the Borlas, but not as good as Xerds. This isn't anything new. The dyno comparison tests for the different types of headers have been well proven on Mustangs 10 year ago.

There is an added advantage to the Xerds that they remove the cats and the cats are the single biggest restriction in the exhaust. Just getting a set of headers without hi-flow cats or straight tubes really defeats the purpose and the gains. It is like you are drinking a milkshake slowly by sucking it through a straw. You want to drink more, but the straw is too small. They make just the very bottom of the straw larger in diameter. The restriction in the rest of the straw is still there and you can't suck anymore through it. A lot of people don't like removing emissions equipment. There are no problems with that, but you have to realize to get the best power out of our cars that there is where a change has to be made.

04' G35 Coupe(finally in the garage)
6-sp Diamond Graphite/Willow w/Premium