hey fisheyOk, so we're talking 2 different plumbing scenario's. The original poster didn't specify how he intended on plumbing it.
I have not had the opportunity to look at how the factory did it but I have looked at how a whole bunch of racers do it and from what I've seen all were plumbed like mine where all the oil flows through the cooler. That's why I said the lines need to be at least 1/2".
when i read your post i figured thats what you were thinkng because i know you know your stuff from reading your other posts .rayer:
as you said if all the oil was going through the cooler then i would want BIG lines on there.
do you need an oil cooler on the street engine well no we all proved that .
does it make an engine last longer under severe duty operations YES .
a marine engine will last about 8000hrs longer with an oil cooler than without one .