not much of a machinist myself, but I'd wager even a hand-drill could get the job done.

The "drilled" part they're refering to above isn't the cast-in holes you see from the runners, but under the pipe-threaded plugs underneath the intake. Cylinder 1 is drilled smaller than the rest... to match the rest of it's casting. If you heat and unscrew the plugs that face the lifter valley you'll see what I mean.

As for the reason... I dunno. "maybe" the millions of dollars of R&D GM does on powertrain controls could shed some light on it... but as mentioned above, I doubt it was accidental. If there was a casting error you wouldn't expect GM to conincidentally make a drilling error as well on the same exact passage... especially over several manifold revisions (92/93 LT1, 94-97 LT1, 96/97 LT4).

I've got a suspicion it has to do with firing order and airflow distribution in those idle passages (you'd need inspect a naked intake to see what I mean).

 

I imagine it's a much different environment with the runners being twice as long... but that's a good question. I have a feeling that the short-runners on the LT1 while great for 5000+ rpms causes some flow issues at idle speed. I'm really just speculating, but I'd bet it has something to due with reversion at part throttle / idle. The daily driver manifold I bought was filthy black... I'd be curious to see how a race-only LT1 looks after similar number of RPMS'.

The other reason is the PVC system that insists on puking hot oil gases into the manifold.

 

No need to heat them, a good ole 3/8 wrench gets them out for me. Hell I milled a intake down just to see where all that stuff went.

Bret

 

Yes that is my reasoning too but since I have a mild cam in there now I can see where GM engineering could use some adjustment.

 

Most of them came out like that for me too, but I grunted like a mad man for 1/2 hour to get one of the plugs loose.

A quick hit with the heat gun fixed it though (wish I'd thought of it sooner). The factory intake I'm working on had red locktite on the brass plugs so in hind-sight the heat could'a saved me time from the get-go.

 

I'm leaning toward EGR...

And wouldn't it be a bit difficult to tell how the inside of an LS1 intake is? I mean, it is basically a black plastic, right? And some of those cars don't have EGR IIRC.

 

Although, I was hinting at what was stated above, regarding runner length, and the air flow pulses, in actuality, it is likely, more of a result of the of EGR. I shouldn't even entertain the issue, as long as the EGR is in the loop.

What, a problem seeing black soot against a black backround? LOL

 

Yes it is EGR, if you look or feel through the TB bores the EGR injects right there at the bottom of the intake (two 1/2" ish holes)