Finished our Woodstock build last week. 2010 F350 Tow Power Plus, host of other mods, including the third version of Steed Speeds. I cannot offer any before and after horse power numbers, but i can offer a testimonial to the quality and customer service. I pulled two classes last night at the RCD pull, work stock and 2.6. The manifolds and up pipes were super red both hooks. While the modified factory up pipes didn't survive the event, the manifolds did great. Already got a call from Leen to make sure all went well. I have the third version of these manifolds, compared to the factory 6.4 or 6.0 that I have, these cannot possibly NOT perform better. The turbos do spool almost instantly and make exceptional boost. I am not on here to make any substantiated claims, just a testimonial to my satisfaction to product quality and customer service.