When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
LT headers might give approx. 15 hp on a bone stock engine. Headers - coupled with a good exhaust system setup - merely SETS THE STAGE for engine and other performance-related mods. Get ready to spend money, there's no two ways about it. The performance gains from headers will synergize everything together as a "package". In the beginning, I tried to fight this but realized if you want real-world performance then you have to pay the piper and consider intake, heads, cam, the works (which included a chip recalibration). Doing it half-way is half-baked. Best thing to do is save the $$ (thousands), take your time and decide. Just throwing headers on will make is sound cooler, and yes will give you some real nice mid-range punch, but it begs of you to do alot more - you have to have a larger plan! I don't know what year corvette your are referring to (no info, nothing in profile), but I'm assuming its an '89 (based on your screen name, unless thats when you graduated), so thats why I mentioned intake and heads (although the heads can be left unported if you can't afford that) as part of the items to consider.
I have the Hooker 2151 headers. My factory pipe had pre cats. The new pipe (Hooker 16720) that fits the headers does not. The y-pipe feeds into a main cat. Even without the precats, my car still passed emission testing.
You have a precat on each side and the main cat, no difference in a CA car these days.
When you do longtubes, you get rid of the manifolds and the front Y-pipe which contains the precats. So then you only have the main cat.
In most states, you can pass emissions testing with just the main cat, so long as the engine is in tune and the main cat is good.
Hooker 2149 contains the hookups for EGR and AIR pump, and has the O2 sensor bung in it, so thats what most of us like. TPiS also makes a good set. You would need the 2149 headers and the 16720 front Ypipe that fits the headers and bolts to the main cat in the same place.