[Paul Workman]

No, nothing sacred about 36mm. But, it does depend on what you are trying to accomplish - specifically - before porting anything.

That said, there are many successful runner examples of builds that are far larger. But!! Runner dimensions are but ONE part of an overall LT5 performance build, AND there are some quirks with regard to the castings of LT5s to be aware of and avoid - or else you may breach the coolant jacket.

For example, many have "siamesed" the intake plenum AND the input to the injector housing. And, the gen-III LT5 did away with the dual runners entirely - secondaries non-existent, i.e, the septum between runners completely gone, thus leaving a wide oval runner, divided just at the dual intake valves.

If you're not a mechanical injuneer, then I would suggest researching extensively what others have done and what the results have been before (and I mean no offense here) "willy-nilly" opening up this and modifying that.

All that said, there is a TON of performance left on the table when the LT5 left MerCruiser!!!