A Silly thing to think about.

[1370rod]

This could be one of the most meaningless post to show up on this forum. Also will mean nothing to people that have not repaired 70 series and later CASE built 6 cly. engines. While assembling a 1070 engine yesterday the same question came to mind as always does while working on them. My guess is others have had the same question occasionally. The nuts securing the intake manifold are those oversize 3/8. We know useing those or the standard size makes no difference. My guess is because they are not the common size and slightly larger cost more. These companys go through great length to save every penny they can, so why in the world would they use those there and no place else on the entire tractor. See I told you it was a meaningless subject, LOL, Rod.
 

[Case Nutty 1660]

my guess it so you get more surface area for torque Rod, on the Alumium manifolds seems to me it would be better even with the washers again just my guess cnt
 

[Mike in Mn.]

I agree 100% with cnt.
 

[1370rod]

Nutty, this is some of the dumb stuff I try to figure out. My thoughts at first were as yours, for more surface area. But they put a lock washer under them so the contact surface area is the same wether large or small nut. They made that move when they went to the alumium intake but they also went to a alumium water manifold which is just as long, has half the number of 3/8 fasteners and has to support a exhaust system on the turbo engines and they changed nothing there when they went away from the cast iron units. Sorry, now I'm ranting. Rod.
 

[jon f mn]

This sounds like something I would come up with while driving threw west Tx. LOL. I too, sometimes have to much time to think.
 

[Case Nutty 1660]

Hmmm yes wasn't thinking of the lock,,,, maybe the bigger nut seals against the lock better, for ensuring no dirt entry and or turbo boost leakage?? cnt