2.4E MFI stack with 2.4T casting number
 

I noticed the R/H plastic stack on my '72 2.4E engine has a casting number which ends with 316 1R. It has the identical bore size (39/32mm) and surface finish with the L/H 911.110.314.1R stack. It has definitely not been bored. Has anyone experienced mismatches like this or have any possible explanation?

The 316 stack is 911T and 314 is 911E.

Dimensions I have measured for 316 are:
ID at top is 35.5 mm
ID at bottom is 32 mm

Dimensions I have measured for 314 are:
ID at top is 39 mm
ID at bottom is 35 mm

Otherwise the stacks have same external dimensions.

Agreed. I meant to say mine are both 39/35.5mm. The 316 stacks I see for sale on eBay are so clearly smaller on both ends that they can be visually identified as "T" stacks. I'm wondering if my 316 39/35.5mm stack is the result of someone at the molding factory mixing up cores and molds.

Possibly, but molds are typically matched and there are different molds for outside & inside (outside has part number and inside has different bore sizes). So the possibility of taking outside of 316 & inside of 314 to make parts is remote.

One caveat: If the external mold has the ability to switch part number then it would be easy to see that one exterior mold could be used for all of the plastic stacks regardless of which inside mold was used. I would check to see if there is a bit of flashing surrounding the part number which would suggest this possible explanation.

http://forums.pelicanparts.com/uploa...1529777741.jpg
http://forums.pelicanparts.com/uploa...1529777763.jpg

1QuickS, I think you nailed it! Not surprising now that I recognize your avatar from the Performance Oriented logo.
It looks like the '31X' part of the part number is made by a changeable section of the mold, so all it would take for a mismatch is to not have correct number creating piece in the main mold.

Yep, same exterior mold with changeable part numbers. You have an interesting intake stack!