I had a new Turbo installed... And made a discovery

[Waterloo]

(04-30-2016 )Rig Wrench Wrote:  561 is slightly smaller. Seen on nore mid level hp cpls. Usually the 551 is on 550-600 hp models. Every big hoid truck ive seen with a 550 and up has had the 551. Trucks with smalker charge air coolers i believe tend to use the 561 for same hp rating.
Just what ive seen. Dunno how much truth there is to it

Well, I have a factory 600hp, do I need to the 551 if I want to run the full 600hp? Am I losing anything or hurting anything? I don't want to dump all of this money in and be short changed or just flat out get the wrong part. Cummins Quickserve calls for the 551, looks like they screwed up and installed the wrong turbo, this is the turbo I need 4309078RX ... I was almost there...