Hole in Heat Riser?

[siteunseen]

I had taken my manifolds off and found this hole under my intake, N47, and was told it was in the Heat Riser. I have taken a sawz-all and "deleted" my EGR from the intake for header install. My Dad says it's nothing to worry about but he's never and will never own a "Furrin Car", he retired from Good Year tire company so he's all about buy American. So I'm asking the Z crowd if he's right or should I buy another intake?

[Zed Head]

These manifolds don't have a heat riser like small-block chevy engine carburetor manifolds do, for example. That passage is the EGR gas passage, if I'm looking at what I think I am (the closeup view makes it hard to be sure) and if you don't block the hole, you'll have a vacuum leak directly in to the intake manifold.

Someone else on this forum had a similar problem, but the hole was not that big. Same effect though.

[siteunseen]

So maybe if I had this welded over it might be ok? Last night I put a mini-mag lite inside of the hole in completely dark garage. I couldn't see any light leaking through, I have removed all the stuff off the top side for a vat bath for all the carbon inside, but I know that air leaks are harder to find than simply using a flashlight. And what I thought was a Dirt Dobbers nest was actually a bunch of sand. Would they use sand for casting? Why has that sand not gotten into the intake other than the EGR passage?

[FastWoman]

Sand left in the casting?! Wow! Maybe some of the sand DID get sucked down the intake.

If you want to know whether your hole leaks is an intake passage, find a way to seal up the intake orifices (e.g. hands held over the mouths of your carbs?), and blow into the intake through your brake booster vacuum line. It will be easy to tell whether the intake is tight, vs. gushing air out through that square hole.

[Zed Head]

I took apart an N47 manifold from a 78 parts car a little while ago and I was surprised at the "sand" also. There was quite a bit inside. Wasn't really sure if it was casting sand or some sort of exhaust residue. I searched around and have seen it proposed that it was actually lead residue but that seems unlikely since they started phasing lead out in the early 70s. Maybe there are other gasoline components that will deposit in the exhaust system.

If you take out of one those allen head plugs you'll probably see a small port in to the intake manifold passage. There is one below each runner. They're very difficult to get out though, I never got one loose. Many people just close the EGR passage off and use the manifold, but the hole to close is much smaller. I blocked mine but haven't reused the engine yet.

[ZCurves]

You could also use the Soapy Water test with compressed air - See where it foams. Since you have already 'deleted' your EGR crap, I would think that you should clean out the funk (sand), weld up everything -especially that giant hole and grind smooth. You could also smooth out some of the intake passages to the head and grind out the Throttle Body port to 60mm for use with a Big Throat or 240sx TB!!