The main difference is that the hy35 has a 9cm2 exhaust housing and the hx35 has a 12cm2 exhaust housing. The hy35 was put on automatics because it allows them to spool quicker, i guess that cummins figured that most automatics would be running around town, so since the hy spools quicker it builds power faster. I suppose that the hx is on the standards because it can flow more exhaust gas and was intended for pulling. Most of the third gen trucks essentially run a hy35, it has a hx40 style exhaust flange, but other than that the turbos are the same.
Tell me if im not makin sence, i didn't get much sleep last night.
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