One of the problems inherent with aluminum intake manifolds is the different expansion rates of the iron heads and the aluminum. The gasket acts as an interface and allows a slight movement.
The gasket sealer that is applied between the gasket and head is to hold the gasket in place while the intake is being installed, and something like Gaskacinch works well.
For the surface between the gasket and intake a very thin layer of Right Stuff smeared on with your finger will help seal the steel to the aluminum and allow a little movement.
Use Right Stuff on the ends.
The intake manifold on the 351-C Ford engine is critical as far as torque rate and sequence are concerned. Intake leaks, although very slight, will affect engine performance and may result in oil burning. Apply the manifold with care, making sure it is aligned correctly, front to rear and side to side, and adhere to the following instructions in three steps.
Installing long studs in the four center holes (9, 10, 11, & 12) will assist in getting the manifold aligned correctly. After torquing the rest of the bolts to their initial torque value remove the studs and install the bolts to their initial torque
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For aluminum intakes:
1. Torque all bolts in sequence to 8 ft. lbs.
2. Torque all bolts in sequence to 15 ft. lbs.
3. Torque all bolts in sequence to specifications:
5/16" bolts should be torqued to 18 ft. lbs.
3/8" bolts should be torqued to 25 ft. lbs.
Be advised that the manifold requires retorquing in sequence to full torque after the engine has reached normal operating temperature.
