Let's talk about a stock computer controlled lt1 with a stock intake and an aftermarket throttle body, like what the thread is about. Lets compare a stock throttle body to an aftermarket one. Now lets all learn something.

 

Do you mean enlarge an already drilled hole? My stock TB had idle air hole already.

 

Yes sir, if you can't get the IAC counts down, enlarging that hole between the throttle bores works well. Doens't take much. If you have a big, close lobe center cam that needs to idle high, like over 1000, that is where I recomend drilling.

 

exactly......on a stock car with a aftermarket tb you should never have to drill

 

Why is that?

 

Again, do you mean drilling a hole or enlarging. As already discussed, some TB's do not have idle holes. Mine did not. It does now and idles perfectly.

 

This is what has worked for me

"if" you have low idle/stalling and have a stock TB on a motor with a aftermarket cam "drilling" out the existing hole 1/64" larger will resolve the idle issue....BUT do not drill blindly as you first need to scan car IAC counts to see if they are maxed out (160 IIRC). The IAC counts want to be 30-35 at idle with engine at operating temp. Once you drill 1/64" larger measure IAC counts again, you may need to drill an additional 1/64" BUT measure IAC first as 1/64" makes quite a diffrence.

Now with aftermarket TB's that have no idle air hole drilled in them like stock and you have a H/C motor with low idle issues you can crack the TB blades open slightly...but you then need to measure your TPS volts because adjusting TB blade position effects the vdc which the PCM reads. You can "slot" the 3 holes in the TPS so you can counter rotate the TPS basically to componsate the same distance you opened the blades up so the TPD vdc reads where it should (.67vdc closed & 4.5 vdc full open BUT there is some variance +/- .67 that is OK at idle)

or drill a hole in the aftermarket TB (start 1/8") and measure IAC and drill in 1/64" incriments until the IAC counts are within spec.

so there are two ways to adjust stock or aftermarket TB's that have low idle issues because IAC counts are maxed. Drill or open blades slightly and also possible slot TPS holes

 

because any aftermarket tb worth a damn ive ever seen for the LT cars has an adjustable throttle blade

I mean modifying the existing with a drill bit lol

 

Any aftermarket throttle body for an lt1 is based off of the 3rd gen castings which has the plenum air exposed to the iac circuit air, unlike a stock lt1 throttle body. Everyone but 2 seem to agree that isolating the air so it functions exactly like factory is the proper way to repair the issues that arise from installing an aftermarket throttle body. Also, aftermarket throttle bodies DO NOT have a hole drilled in the throttle body for the iac circuit when a stock throttle body does. Again, the proper fix for this is to drill the throttle body until desired hot idle iac counts are achieved. These two mods allow for aftermarket throttle bodies to function as the stock one would. These mods are significantly documented as well as the problems being rectified after they are performed. So again I ask, why?

 

I guess a parabolic slit vs a round hole with the same area makes a difference, who knew. Please sit tight im going to call GM and tell them they've been doing it wrong since 2005.

 

I'm not sure if you are ignorant, too full of yourself to be wrong, or just an idiot. We are talking about 92-97 lt1 motors here. We are talking about modding aftermarket parts to function like oem, like they should. We aren't talking about later year parts and how they operate.

I usually read your posts as well as Ed's with respect and an open mind, I typically learn something. I don't know why this is such a difficult thing for the two of you to grasp, have you not messed with stock style equipment in a long time?

 

Could be you have read too many internet message board threads written by other people with probably no more actual testing experience than you? Could it be that some people have done testing to measure cylinder-to-cylinder air/fuel ratios, instead of going by what some key board jocky has reasoned out in his head must be the case.

If you know Mike Acton, ask him about the O2 bungs in the headers be bought from me.

You do know there are individual cylinder fueling tables in the factory PCMs?
Easy fix right there. The factory IAC and cylinder-to-cylinder fueling all goes out the window when heads and intakes are ported. If you ever actually tested and measured things, instead of just typing, you would know this.

How fast is your stuff anyway?

 

 

your completely overlooking what I said in an attempt to call me ignorant or perhaps and idiot? id like to think not, when it comes to electro/mechanical controls I have a bit of experience in the area over the normal person

 

Ed, I personally had an issue with maxing out my iac counts and bank to bank imbalance on my car with a tpis 58mm throttle body. I found the issues with the iac circuit being exposed to plenum air unlike a factory throttle body. I also found no hole in the iac circuit, unlike a factory throttle body. I simply replicated the factory iac circuit on my throttle body, cost me nothing, and I have a car that functions just like factory, except with a bigger throttle body!

I'm sorry, I don't know the Mike you are referring to with 8 bungs. I'll ask around though.

How would tuning individual cylinders via the fueling tables be a simple, cost effective solution here? Most novices that own these cars don't get into tuning their own car, they either mail order or dyno tune them. So if the factory iac and cyl to cyl tuning all goes out the window when heads and intakes are ported, why did you mention doing it? Do people stick 58mm throttle bodies on stock head/intake cars? Seems kinda dumb to me, must be an internet thing though. Oh you know what is weird? My car has ported factory heads with a ported factory intake AND a corrected 58mm throttle body AND EVERYTHING WORKS FINE! Bank to bank is damn near perfect, just had the injectors cleaned to really balance the banks. I wish I had the money to stick 8 bungs in my primaries and really get things done! For now, I'll stick with the factory bank to bank comparison and let my factory computer do its thing.

How fast is my stuff? Its slow, according to you. Then again, its a car I hop in and drive to the grocery store with. Its a car I let sit for a couple months then drive to a track rental, race, and drive back home. Its a car I built to drive on the street and race a handful of test and tune nights a year, if that. Its a car I drive to work any day I please. I'll tell you what though, it does exactly what I want and when I want! So Ed, how street worthy is you stuff?

Sorry, I assumed when you said 2005 you were referring to electric throttle bodies and the whole lack there of an iac motor/circuit like the 92-97 lt1 motors use, something that Ed brought up. I'm not sure how nearly a decade later's technology applies here? I just try to provide useful, tested, and good information when I can.

 

I dug up some pics, maybe it'll help.

Stock: Note hole in IAC circuit


58mm: Note no hole in IAC circuit


Stock: Note hole in IAC circuit and enclosed IAC circuit, open evap circuit


58mm: Note no hole in IAC circuit and open to plenum IAC circuit, open evap circuit


Ported stock intake: Note enclosed IAC circuit and throttle body openings ported to approximately 58mm


Ported stock intake runners: Note IAC circuit feed holes in ported runners, faint dark spots


New 58mm TPiS Throttle Body with corrected IAC circuit

 

Excellent post, 5 star tech, would read again.

 

If you tuned enough cars you would find as many stock TB head & cam cars with skewed fuel trims as with aftermarket pieces.

It's not just a bank-to-bank, it's cylinder-to-cylinder.

Nice pics, but I would assume everybody knows what those parts look like.
The factory tuning has most cylinders trimmed differently at closed TPS, different yet at open TPS. The B body cars are different than the F body cars, the LT4 is different yet. Those change with a bigger cam and porting, and more often than not need altered. Less than half don't require tweaked. Each bank's trims are only an average of that bank. Without 8 wide bands all we have are EGTs. If you do enough of this you learn with popular cams & heads how to even them out a bit closer. If, without tweaking cylinder-to-cylinder trims, drilling your TB made your trims even your lucky. I'm happy for you. :-) Doesn't work out that way for many.

Sometime when you have that manifold off, and want to make more power, you need to cut the top off and put a larger radius at the runner entries would pick the flow up a good bit. It is worth some power. Take it off with a band saw, and TIG weld it back on. That is a flow restriction right there.