I was cleaning up a 97 LT1 intake yesterday and found something that kinda worried me since I am planning on bolting this onto my car next week. Looking down into the intake runners I noticed there is a small hole in each runner which I am sure is just the IAC ports or passages but the hole to cylinder #1 is nearly 1/2 the diameter of all the rest!?

Why would GM do this or does my intake just have a flaw that needs to be fixed? I am really hesitant to bolt this on my car b/c like I said every other port is the same size but #1. Sorry if my question isnt advanced enough for this area.

 

That's not going to make much of a difference. That hole does go to the IAC but since there are 7 others it will be fine. On top of that most motors don't even bother to have it routed to every cylinder like that.

Bret

 

The main reason for GM doing this was the extreamly short runners and idle quality.

As Bret said most engines do not bother with this

 

Yeah I understand that... I was only wondering why #1 was so much smaller than all the rest of the cylinders b/c it could conceivably cause idle problems.

 

First off, cuz the hole is drilled, it is not a flaw or mistake. If you were familiar with production drilling operations, it wouldn't be possible to have one hole of a diff size, unless intended. BTW, the earlier manifolds are the same.

I believe that is the very reason why the hole is of a diff size, as compared to the others.

 

Are you talking about the port itself? Or the hole in the port?

The reason I ask is because when I had my intake off one of the intake "ports" were quite a bit smaller, say .150-.175 in. narrower. I opened it up with a die grinder to the same size as the others. My guess is core shift, anyone elese witness this?

 

I was talking about the small hole in the floor of the port.

 

I'd guess that the first hole is smaller because it's so close the the throttle body?

 

It is not a design flaw. They are intentionally designed that way to balance the airflow to each cylinder at idle.

If you happened read all the posts about the split BLM's on cars with aftermarket t-bodies (most do not bleed air to these passages, they just dump it in behind the butterflies), you would see the benefit that these passages serve. The different sizes just help to improve idle quality.

The LT4 intake has a different size air passage at #1 as well.

 

You learn something every day! I never even noticed the holes in the first place, let alone that they are different sizes. Thanks for adding to my store of automtive near trivia.

Rich Krause

 

You have to be kidding right? LOL how else do you think idle air gets in through IAC? Yeah I noticed that a long time ago, I figured since the first port always will have most of the air that goes past the butterflies while the other ports won't, so if you keep the other holes big & the two front ones small, it will balance itself out because the two front ones will also get 90% of the butterfly air. If the hoels were the same, the front ports would have the same IAC idle air distribution & the extra 90% of the butterfly air which would cause an imbalance, hope this makes sense.

 

How is your figuring altered if I inform you ONE front hole (#1) is of reduced size, other front one is not.

If the holes were the same, the front ports would have the same IAC idle air distribution & the extra 90% of the butterfly air which would cause an imbalance, hope this makes sense.

Makes sense? Right up to the point of informing you #2 is not included in your reasoning.

 

I could have sworn I saw both small on mine wtf! I think I'm going blind, I even ported my intake manifold LOL.

 

Actually, if ya want to talk about design flaws, anyone, ever take off the TB and NOT find black 'soot' in the intake plenum? What is that tellin' ya?

Thot I should add this: anyone find as much soot in the LSx intake plenum upon inspection?

 

lol, saw the holes but thought they were emissions related...

as for the soot, yeah, i was wondering about that myself.. the only thing that should be in there is air and possibly nitrous... lol...
so why does it get so nasty in there?
are the lsx's cleaner? never worked on one...

there are many design flaws...but i don't think that was one, as for the holes being drilled, i don't think so... how can you get a drill bit in there??? if so your a better machinist than I.