What kind of power gains can I get from aftermarket headers?
Edelbrock TES Viper headers are good for a solid 18 rw hp gain, and are claimed to be the ONLY headers that have been granted an E.O. # which makes them the only 50-states street legal headers on the market. The increases that have been made with their newer design, as well as the rest of the TES applications they offer, are very significant when working within the constraints of staying emissions legal with an E.O. #. Edelbrock claims they could undoubtedly manufacture a set of non-E.O. # TES headers that make quite a bit more power, but as everyone knows Edelbrock is dedicated to offering emissions legal performance products with E.O. #'s for all late model vehicle applications.
SVSi headers are good for 45 Hp and 51 ft.lbs. of torque w/o cats. 3" exhaust With the cats on 38 Hp and 40 ft lbs. torque 3" side exhaust. These are just peak numbers. Low end torque came on faster and was considerably higher.
Hennesseys stainless steel headers show an improvement of 24 - 28 hp depending on their mods.
SVP headers (which are Jet Hot coated inside), combined with the SVP Tailpipe system, showed a peak improvement on a Stock Viper GTS Coupe of 42 rear wheel hp.
Also on a GTS, a gain of 41 hp (rear wheel) with SVP headers and no cats has been documented,as well as someone else who gained 45 hp (rw) with SVSi headers and no cats.
Here's another simple exhaust mod: toss the muffler and put in a straight pipe with balance tubes. Idle is a hair louder, but not too bad. This mod is good for 12 to 15 hp. The sound is truly awesome, as well. Yes, the Viper responds well to a freer-flowing exhaust!