needs to be atleast three letters and a date.My YDD was a breeze,dealer told me everything about my truck.My 599 block is a YWD and nobody can find that.I guess i have a mystery engine.Was thinking maybe it was a speacil order.
There's 4 different 6.5s out there...
'F' - HD Turbo
'S' - LD Turbo
'P' - LD Non Turbo
'Y' - HD Non Turbo
So its a 6.5 with a mechanical injection pump (either 5088 or 5436) and probably a mechanical supply pump and no EGR.
Very reliable with the mechanical pump and no EGR is always a plus, as far as performance, about all you can do is upgrade the exhaust with bigger pipe and free flowing muffler, fresh injectors and maybe tweak the pump or have it tweaked at a fuel shop.
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