Choosing gaskets for the Gen 3 60V6.

Gen 3 was the start of using plastic lower intake gaskets, and the reputation they garnered will never go away. There has been revisions to both the gaskets, and the installation process. Most notable is the use of a thread locker to keep the lower intake bolts from backing out.

For the 3100 and 3400 engines, you have 3 lower intake gasket versions. A plastic lower with no metal tabs, plastic with the tabs, and a metal gasket. Besides the small port 3100s using a different gasket set for the lower intake alignment pin location, they are all the same in design for what is being discussed. For the record, all 3 versions can be successfully used, if you really want to. The plastic versions use the same port shapes so no difference other than the metal tabs used to help keep the installer from breaking the gasket from over tightening the bolts. The metal gasket has a much larger port shape, which is what we want. Not for porting potential, but for the space that gasket is going to take up once you torque the manifold down. On a stock engine, this is the end of the story for the 3100/3400. For performance/ported top ends, you might consider taking a knife to the ID of each port and cutting the rubber out to the metal. You aren’t porting to this but if you got close to matching anywhere near the gasket, this will keep the gasket from squishing into your space.

The 3500 LX9 is in a different position. They have a plastic lower with tabs, and a metal gasket. You want the Mahle plastic lower intake. It is the closest to the original gaskets, which is ideal. The metal gaskets are all smaller port sizes. No advantage for porting, and you MUST cut the rubber out of the ID of the port or it will restrict flow. The Mahle set also comes with metal upper gaskets, which are a nice to have (at the time of writing this).