You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re exploring a technique for proper intake manifold-to-cylinder head sealing.
C.M. Chicago, IL
Q: I purchased a set of Edelbrock aluminum heads for my 1979 Corvette 350 engine. The engine has a 280-degree duration solid lifter camshaft, 10:1 compression pistons, and an Edelbrock Performer RPM intake manifold.
The problem I am having is that I can’t stop oil from leaking into the intake runners. My vacuum is low, too (8-10 pounds). I contacted Edelbrock and was advised to return the heads to them. They checked the heads for sealing and leakage, but could not find anything wrong with them. Since I put the heads back on the engine, I changed the intake gaskets three times and intake once. The problem is still there.
I had no problem with the old cast iron heads. I took the engine to a local engine builder, and he said the block was not cut or decked, just bored .030 over. I would appreciate any help you could provide.
A: Misalignment is a very frustrating problem, especially with lightweight aluminum heads and intakes. Here is a procedure you may want to try to get those parts to seal up:
- Check all mating surfaces with a straightedge to make sure they are truly straight.
- If surfaces are straight, place Fel-Pro #1204 intake gaskets on the heads and set the intake manifold in place.
- Check for any mating surface gaps with a .003-.005-inch feeler gauge. If there is a gap on the lifter valley side of the intake, then the mating angles are off and the intake needs to be corrected. If no gaps are found, make a visual note of the block-to-manifold gap width.
- Remove the intake and place a large bead of Permatex Ultra Black silicone sealer on the black mounting surfaces (front and rear).
- Lower the intake back on the engine. Following the manufacturer’s recommended torque sequence, torque the intake to 30 ft.-lbs. in 10 ft.-lbs. increments.
- Let the intake sit six to eight hours to let the silicone set. After several days of use, check the bolts to make sure they are still at 30 ft.-lbs.
Same problem here. Used permatex #2 all around the intake runners on both sides of the intake gaskets, which seems to have taken care of the issue. Put gaskets on dry twice before and ended up with the same problem the OP described both times. Never had to do this with my iron heads.
Believe it or not the Fel Pro intake gaskets do not have enough compressability. Too hard. I would not use Fel Pro gaskets except they have cornered the market and it is impossible to find a brand that is better. I use a thin coat of high temp “red” silicone on all of my Fel Pro gaskets.
Same problem here on a Gen one 350. Edelbrock aluminum heads, Edelbrock aluminum intake (Brand new) Felpro gaskets and the intake still leaks air. Used a straight edge and the mating surfaces are straight. Never had this problem prior. This will be my 4th set of gaskets. I’m at my wits end with this GM nightmare! Should have stayed with Ford! Should have known better! Who puts the distributor on the rear of the engine!