2010 Vette GS M6 pending extensive mods next year (if Trump gets re-elected). Not new to this game at all - thought I'd chime in.

I've had MANY performance cars with header systems over the years. In studying the header needs of this LS3'd Vette, I can't recall any header install improving rwhp/rwtq as generously as the headers available today for this car. That said, they're also the priciest headers I've ever encountered for basically a street car...ie: the headers are routed in the same path as the stock exhaust. There are several top-line manufactures out there, each with their own twist on getting the most power enhancement out of the exhaust flow. Recall that a header has zero moving parts, and is designed to convert the hot pressurized flow of spent exhaust gasses into useable kinetic (mechanical) energy. The commentary that follows is simply sharing my experience & research on the topic of headers, relative to the C6 and LS3.

1) Makers I'm paying attention to, due to design, workmanship and reputation for 'consistently' making good power: Stainless Works, ARH, Kooks, LG, Texas Speed, and Corsa. There are certainly several other out there, and cheaper: Hinson, Speed-Engineering...etc, but I can't speak to those.
It's important to note that just about ANY traditional 'long-tube' header will increase the power of your Vette..... but there are factors to consider: by how much money, how hard to install, how much power, how long before there's a crack in a weld, flange or pipe, what grade of SS are they made of...etc..etc.. Do your research and you'll start to see a pattern and why there are 4-5 dominant manufacturers here and elsewhere.
2) 1 3/4" primaries are 'said' to produce more low end tq under the curve vs 1 7/8", however I have seen many MANY builds using 1 7/8" and the dynos, most showing little to no loss of low end tq and a bit more hp above 5K rpm. BUT one would be wise to also take note of the build sheet, especially cam specs, and heads or head work. It's my opinion that the less aggressive builds (usual external mods) tend to respond well to the smaller primaries. More deliberate builds which include cam, heads, intake manifold...etc., yes, those will make better power with 1 7/8", BUT it could still be fine with 1 3/4"... it just depends, ha... If you're going blown someday, then 1 7/8" is a must, but 2.0" could be better, depending on the cam! That said, overall it seems the 1 7/8" is the go-to/most popular primary size I see. Nope - no one answer.....
3) Longer primary tubes DO make more tq under the curve, proven many times, but how long is LONG? Kooks are the shortest, followed by ARH, then Stainless Works and Tx-Spd are tied with very long primaries. LG super pros are a mix: 1 3/4" are super long pipe-organ primaries, while the 1 7/8" are about the same a Kooks. ALL of these headers make ABOUT the same +/- 7-10 hp/tq... relatively speaking. The total build has a LOT of pull on how well a header performs = The Engine mods need to compliment and balance with eachother.
4) The Collector< THAT's a very important piece of the header puzzle. A well designed 'merge collector' will definitely improve scavenging impact of a given header system, and where the collector is placed, plus if there's a merge spike installed. ARH, Kooks, Tx-Spd and LG's Super-Pros, all have excellent merge collectors, with the spike. Stainless Works uses the spike only with the collector 'shape' being noticeably less merge-like, however they do make about the same power as the others, so what's that mean? Read their material, as they claim to have a better mouse-trap, ha... and maybe they do, but they're spendy!
5) X-Pipe design also plays a role, albeit a smaller one. Only ARHs has the crossover placed directly at the exit of the merge collector. There have been debates about this design upsetting exhaust flow pulsations & harmonics, however I've not seen any negative impact on any dyno chart. I do know that placing the crossover farther away from the collector (and after the Cats if installed) produces a noticeably deeper exhaust tone, if one is interested in that.
6) Fitment: NO PART of the hear & X-pipe system can touch the car, except at the block and applicable hangers. Some of these headers can be a royal pain to install, especially in 1 7/8" or larger. A couple (above) require loosening the starter, or even raising the engine in order to gain needed clearance for the header install. ARH notes that some 'trimming' may be needed, as noted in a previous response. Such 'trimming' is not a big deal at all, BUT it certainly indicates that pipe is damn'd close!!

Okay, ok...that's my 2 cents and then some, ha... NO I have not yet chosen or purchased my headers, but it will be one of them, except for Tx-Spd... which is VERY regrettable! I'm just a normal guy like the rest of us here. No affiliation with any manufacturer or any of that other crap. After 6 decades of life, I've built many performance cars, race engines, have raced cars (and boats and motorcycles) and now I've this C6 Vette and its LS3, just LOVE it. Oh.. as for Tx-Spd: It's the lowest priced 'quality' system out there by approx 50% LESS, and the header is a really a great design with long flowing primaries (like Stainless Works) and has a great merge collector, BUT but and I mean butt... they hang low, LOW, and they can/do scrape and dent, plus they don't offer a Catted X-pipe... So yeah, I'm out - off my list... They should do a re-design, tuck those pipes up... geez! Stainless Works is very similar in design, BUT they're primaries are tucked up nice and tight. Whatever...

And so - Good luck to you sir. I hope this helped in some way on your quest - "never stop asking questions!"

 

I was one of those who choose (Maryland speed) to buy my Kooks They were a s,,,,, company and have been put out of business under that name. Was told to expect a long wait because they had to ship to (Jet Hot) and they would ship them to me.
Almost 9 weeks from order to receiving them. Am happy with the pipes ,after getting them.

I did use OEM exhaust gaskets much better quality gaskets than Kooks provided. I also used stage 8 header bolts although others allowed OEM bolts were acceptable. Just my call and glad I followed my own advice!

 

Thank you for the info. It appears, I will buy direct from Kooks (offering a 10% discount.) Have rhem ship direct to Jet-Hot.