074 heads extra holes in intake ports

[Jeff M.]

On my 71ls6 074 heads there are extra holes in 2 of the intake runners on each head, I am told they were for the zl1 alluminum block. They are not used on steel blocks. The question is, should they be plugged? If they are not plugged, what effect do they have? I have been told that it will create a vacumn leak? What about oil consumption. Can I plug them with rtv or jb weld while in the car by removing the intake.does the head gasket cover the open hole

[Joe L.]

Re: 074 heads extra holes in intake ports

On my 71ls6 074 heads there are extra holes in 2 of the intake runners on each head, I am told they were for the zl1 alluminum block. They are not used on steel blocks. The question is, should they be plugged? If they are not plugged, what effect do they have? I have been told that it will create a vacumn leak? What about oil consumption. Can I plug them with rtv or jb weld while in the car by removing the intake.does the head gasket cover the open hole

Jeff-----


Yes, the holes are for the 2 extra head bolts used for ZL-1 applications. These holes should be tapped for7/16-14 thread size. You can plug them easily with allen head set screws coated with sealer.

[Clem Z.]

Re: 074 heads extra holes in intake ports

Jeff-----


Yes, the holes are for the 2 extra head bolts used for ZL-1 applications. These holes should be tapped for7/16-14 thread size. You can plug them easily with allen head set screws coated with sealer.

i used loctite because you don't want them to come loose and get sucked into the intake port and into the engine

[Jeff M.]

Re: 074 heads extra holes in intake ports

What happens by leaving them unplugged

[Clem Z.]

Re: 074 heads extra holes in intake ports

What happens by leaving them unplugged

you will have a BIG vacuum leak and you will suck oil out of the tappet chamber

[Jeff M.]

Re: 074 heads extra holes in intake ports

This could explain the oil consumption,I have run these heads without the plugs for years.

[Clem Z.]

Re: 074 heads extra holes in intake ports

This could explain the oil consumption,I have run these heads without the plugs for years.

WOW that is amazing because i would think the vacuum leak would cause tuning problems.

[Jeff M.]

Re: 074 heads extra holes in intake ports

I have 16 inches of vacumn at 900 rpm???

[Joe L.]

Re: 074 heads extra holes in intake ports

I have 16 inches of vacumn at 900 rpm???

Jeff------


The holes must already be plugged or the head gasket has enough overlap that it's effectively plugging the holes. I doubt the latter, though.

[Clem Z.]

Re: 074 heads extra holes in intake ports

Jeff------


The holes must already be plugged or the head gasket has enough overlap that it's effectively plugging the holes. I doubt the latter, though.

i agree as the vacuum leak would be horrendous if the holes were completely open