On a stock LT1 throttle body, there is a straight hole from the front into the IAC passage...




A BBK 58mm TB does not have the straight through port. but it has an opening in the back side that would allow air to get into the IAC passage.





If you close off this passage (either using copper tube or welding it up to look like a stock)



would you have to drill a hole in the front to make it work. Does the IAC passage need AIR to get into it besides what comes through the IAC?

I welded my 58mm bbk up to make it act more like stock to help fight the split BLM's... and now i am getting all sorts of weird stuff happening.. really odd split blms and other stuff. its the only thing that was changed besides taking the intake off and replacing a oil drive gear.

 

link to the weird stuff with a datamaster scan, just cant figure out what is going on. http://www.impalassforum.com/vBullet...d.php?t=242958

 

I had a really good post on this subject over on tech.

Let me throw my two cents in. I have the 58mm BBK TB and I had to drill the hole in the IAC because the IAC counts were much too high. I used the same size hole that the OEM TB uses. This brought the IAC counts to around 30-40 or so. Problem fixed.

I then had nasty split BLMs at idle and to a lesser degree, everywhere else. As you have already seen, the aftermarket TB's, drop the idle air right into the large plenum and then it does not efficiently distribute to all the intake runners. This cause the split BLMs.

The OEM sends the idle air into the small hole on the front face of the intake manifold then into a much smaller plenum on the bottom side of the intake. The air is then evenly distributed through the small holes in the intake runners and each cylinder gets about the same amount of idle air.

So clearly all of the aftermarket TB's makers have chosen to not use the OEM engineered idle air circuit and this causes most folks to have crazy BLMs. Thanks BBK.

So I had my engine builder machine out an area of the BBK TB so we could then machine a plug to not allow idle air into the large main plenum. The plug was drilled to force all idle air into the small hole on the front of the TB and into the small holes in each runner just like GM had intended for the LT1.
Here are some pics of my TB mod:



Final result.
128/128 BLMs at idle 95% of the time.

 

So the question was... (you kinda stated everything I did already except the hole drill)

would you have to drill a hole in the front to make it work?
Does the IAC passage need normal AIR to get into it besides what comes through the IAC?


Reason I am trying to differentiate, I have read many posts that talk about drilling, and I have read posts that talk about isolating the IAC passage, but I have NOT read both being done at the same time (besides yours now)...

 

Yes I had to drill the hole to amke it work to get the IAC counts to an acceptable middle of the road range.

 

What size drill bit did you use?