99% is a bit strong. Most main stream SLP/Kooks etc will not throw codes - I have kooks headers, high flow cats and Mach XL Catbacks, no codes yet and no tune. As for your choice --- its huge, JBA, Corsa, Kooks, SLP, Stainless, pacesetters the list goes on....
True - a tune will benefit if you fit LT headers. But I have found this combination sounds fantastic, and adds HP without a tune (SLP say 25hp advantage without a tune)
Shorty headers - do a search and you'll find that they do not add much if anything in HP gains
If i had any warranty concerns i could simply re-fit stock headers and take it in. 5500 miles and no complaints
Stick to Catbacks if you want to retain warranty
As for tunes and warranty
Don't go there!!!
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GET-TORQ custom CAM 223/243 LSA113, Full LS3 conversion, 3200 stall Multi-Disk TC from Circle-D, B&M Supercooler to cool that tranny down....1 7/8" Kooks Headers and High flowCats. MACH XL Catbacks. Eibach springs, R2C Performance CAI, powdercoated calipers, Footwell lighting in tune with dome lights, tints, ABL Lighting, ACS T3 ports and ACS Eagle T3 triple LED lighting kit. Heritage grill, Hex vents, ZL1 rockers, ZL1 Diffuser, Quad tips...the list keeps getting longer - whats next??