Posted By: DrCharles
Intake manifold leak - 04/15/23 03:35 AM
As posted previously, I finally put my PRH-ported Speedmasters on my 451 Dart, and drove it to the first-of-the-season West Plains Car Club cruise-in at Steak & Shake!
It seems I have a little work to do - the (Performer RPM) intake manifold must not be sealed properly so it idled rougher, less vacuum, and AFR leaner, and when I let off the gas on the highway and hit it again, a puff of blue smoke comes out the tailpipes. All of those are classic symptoms of intake leaks sucking oil from the valley.
I re-used the valley pan (once) and brushed on Permatex #2 for the sealant on both sides of the pan (Ultra Black on the ends).
The manifold feels just a little too high in the V and the bolts wouldn't start. I rat-tailed the holes in the intake just a few thousandths (barely removed the paint) and then all eight would go in. (The heads were cut .055 I think, but obviously Dwayne knows how much to cut the intake surface) Also retightened the bolts.
Another variable is the lash on my lightly-reground Mini-Express. Schneider recommends .018", so I set them to .012" cold, expecting the typical .006 growth of the aluminum head on iron block. Previously with the iron heads, I'd set the lash "a little" looser than the usual +.002 for break-in, but don't remember how loose, and never got around to readjusting the valves in, now 1370 miles.
So I'd expect some vacuum drop at least until the engine warms up, and maybe even a leaner AFR due to the increased overlap (charge dilution) with tighter lash? But valve timing wouldn't cause the puff of oil smoke... that has to be oil getting sucked in to one or more ports since the guides and seals are all brand-new... also, when I abruptly let off the gas after accelerating to 5200 rpm, I could actually hear an intake sucking sound...
My plan is to experiment with propane or carb cleaner. Luckily the big-block is an easy manifold removal. I'll get a new valley pan, and use a thicker sealant. Probably Ultra Black unless everyone says to use something else
thanks for any tips.
-Charles
It seems I have a little work to do - the (Performer RPM) intake manifold must not be sealed properly so it idled rougher, less vacuum, and AFR leaner, and when I let off the gas on the highway and hit it again, a puff of blue smoke comes out the tailpipes. All of those are classic symptoms of intake leaks sucking oil from the valley.
I re-used the valley pan (once) and brushed on Permatex #2 for the sealant on both sides of the pan (Ultra Black on the ends).
The manifold feels just a little too high in the V and the bolts wouldn't start. I rat-tailed the holes in the intake just a few thousandths (barely removed the paint) and then all eight would go in. (The heads were cut .055 I think, but obviously Dwayne knows how much to cut the intake surface) Also retightened the bolts.
Another variable is the lash on my lightly-reground Mini-Express. Schneider recommends .018", so I set them to .012" cold, expecting the typical .006 growth of the aluminum head on iron block. Previously with the iron heads, I'd set the lash "a little" looser than the usual +.002 for break-in, but don't remember how loose, and never got around to readjusting the valves in, now 1370 miles.
So I'd expect some vacuum drop at least until the engine warms up, and maybe even a leaner AFR due to the increased overlap (charge dilution) with tighter lash? But valve timing wouldn't cause the puff of oil smoke... that has to be oil getting sucked in to one or more ports since the guides and seals are all brand-new... also, when I abruptly let off the gas after accelerating to 5200 rpm, I could actually hear an intake sucking sound...
My plan is to experiment with propane or carb cleaner. Luckily the big-block is an easy manifold removal. I'll get a new valley pan, and use a thicker sealant. Probably Ultra Black unless everyone says to use something else
thanks for any tips.
-Charles