What is this hole for on the lower intake? I happen to see it and I'm wondering what it's for or what might suppose to be there.

 

That looks like the spot where the anti knock sensor used to go. Just about centered front to back ?

 

Yep. Will that hurt anything with it not being there?

 

Depends on the year of truck if it's even supposed to have one. but if there's no sensor it should have a threaded plug in it.

 

Well it's a 87 and there isn't a plug in it

 

Does your truck have an ACT sensor on it?

 

What's a ACT sensor

 

Don't know if you're supposed to have an anti knock sensor or not (probably), but until you get it sorted out, you should get a threaded plug or even a bolt to plug it.
That hole will be wide open into your lifter galley. Maybe not WIDE open, but crap can get sucked in there, plus your pcv won't work right and ... well all kinds of things can happen - none of them good.
Just find a short bolt that fits it for now.

 

Ok

 

+1 to what he said. You dont want anything foreign getting inside your intake. If you introduce substances and debris to your well oiled machine, well, it no longer becomes a well oiled system.

My best buddy is really into nostalgic drag racing. His entire family is. Last summer, I spent a good deal of time at the barn helping him work on his Falcon. This barn is also home to many cars that race 9s and 10s on the eighth mile. So, I got to learn a great deal about "performance" cars and parts. Anytime an engine was not in a vehicle, you could count on the fact that there would be rags shoved in the openings for the intake. You dont want anything inside there. They even had a front-end dragster, with some vertical pipes for the intakes. At all times other than go-time, there were these rubber ***** in each of the pipes to prevent debris from entering the system.